Start-up Aid for PCs

Since one of the servers owned by the author would not start up by itself after a power failure this little circuit was designed to perform that task.

The older PC that concerned did have a standby state, but no matching BIOS set-ting that allows it to start up unattended. Although a +5 V standby supply voltage is available, you always have to push a but-ton for a short time to start the computer up again. Modern PCs often do have the option in the BIOS which makes an automatic start after a power outage possible. After building in the accompanying circuit, the PC starts after about a second. Incidentally, the push-button still functions as before.

 Start-up-Aid for-PCs-Circuit Diagram

The circuit is built around two golden oldies: a NE555 as single-shot pulse generator and a TL7705 reset generator. The reset generator will generate a pulse of about 1 second after the supply voltage appears. The RC circuit between the TL7705 and the NE555 provides a small trigger pulse during the falling edge of the 1 second pulse. The NE555 reacts to this by generating a nice pulse of 1.1RC. During that time the output transistor bridges the above mentioned pushbutton switch of the PC, so it will start obediently.


Other applications that require a short duration contact after the power supply returns are of course also possible.


Author : Egbert Jan van den Bussche – Copyright : Elektor

555 Timer Travel Touch Alarm

The Travel Touch Alarm can be used to provide a audible alarm  when someone touches the door knob or handle of your hotel room. The door knob or handle must be made of metal for the circuit to work. The main chip in the circuit is a 555 timer which will be triggered if a hand comes close to or touches the door knob.

555 Timer Travel Touch Alarm Circuit Diagram

555-Timer-Travel-Touch Alarm-Circuit Diagram

The circuit attaches to the door knob at the end of the 1 meg ohm resistor. Once the timer is triggered the LED will light and the UJT will output a tone to the speaker. The timer will time out in 5 seconds. The sensitivity of the trigger can be changed by changing the 1 meg ohm resistor to another value. The 5 second time out can be adjusted by changing the value of the resistor connected between pin 8 and pin 7. The output tone can be changed by changing the RC values on the base of the UJT.

Clock Pulse Generator

For many years the author has been approached by people who have managed to lay hands on an ‘antique’ electric clock and need an alternating polarity pulse driver. This is immediately followed by the question whether an affordable circuit for this is avail-able. The design described here has been working very nicely for years in three of the author’s clocks. To keep the circuit simple and thus inexpensive, the author dispensed with automatic adjustment for summer and winter time.

A 32.768 kHz oscillator is built around IC1. X1 is a crystal of the type that can be found in almost every digital watch, especially the cheaper ones. The frequency can be adjusted with trimmer C1 if necessary.The clock signal is divided by IC1 and IC2 to obtain a signal on CT=6 (pin 6) of IC2 with a frequency of one pulse per minute. IC3.A is wired as a divide-by-2 circuit to maintain a constant signal during each 1-minute period. IC4.E and IC4.F buffer this signal, and IC4.D inverts the output of IC4.F.

Clock Pulse Generator Circuit Diagram


When CT=6 of IC2 goes high, IC3.A receives a clock pulse and its Q output goes High. IC4.F and IC4.D then charge C3 via R6 (1 MΩ), and the output of IC4.C remains low for approximately 1 second. This drives T2 into conduction, and with it T1 and T3. The resulting cur-rent through the clock coil causes the green LED to light up. When CT=6 of IC2 goes high again after 1 minute, IC3.A receives a new clock pulse and its Q output goes Low. Now C4 is charged by IC4.E via R7 and the out-put of IC4.B is low for approximately 1 second, so the output of IC4.A is logic High. This drives T4 into conduction, and with it T5 and T6. The resulting current through the clock coil causes the red LED to light up. In this way the clock is driven by pulses with alternating polarity.

Diode D7 protects the circuit against reverse polarity connection of the supply voltage. Diode D8 is lit constantly when the supply voltage is present. Transistors T7 and T8 provide current limiting if a short circuit occurs in the clock mechanism. The peak pulse cur-rent can be increased by reducing the value of R16 (minimum value 2.2 Ω). Diode D11 is a dual suppressor diode that clips any volt-age spikes that may occur. This diode is fairly expensive, so it was omitted in the circuits actually built. This has not led to any problems up to now, but it may be advisable with heavy-duty clocks or multi-pulse clocks.

Note: this circuit is only suitable for pulse-driven clocks that operate at 12 V. The circuit must be modified for models that operate at 24, 48 or 60 V. As these models are less common, or in many cases can be converted to 12 V operation, this option is not described here.


Author : Ed Flier - Copyright: Elektor

Intermittetly Pulse Generator

The generators of square pulses, are used in a lot of applications, between which the adjustment of conditions of entry in the digital circuits and the control of amplifiers acoustic frequencies. This circuit is a generator that it produces, in combination with a other generator, sine wave frequencies or square pulses, continuous or interrupted square pulses. Main characteristic the generator it is, that the circle of operation can be regulated so as to he is constituted from until ten interrupted pulse.

This pulses are particularly useful for the adjust amplifiers, loudspeaker, rooms of hearings etc. A other qualification of generator are that her pulses have level of report the 0V, without it is used for aim, capacitor in the exit. The absence of capacitor in the exit, has as result the production of clearly square pulses in any frequency of operation. The generator work without perceptible distortion up to their 100KHZ.Her pulses have width 5Vpp (± 2.5V) and cover the needs of all amplifiers acoustic frequencies.

In the cases where we needed signal of smaller width, then we can him decrease with the pontesometer RV1. The generator is supplied with ± 5V, provided from two batteries or from one suitable power supply. Placing the S1, in different places from the 1 until 10, (a place each time), the crowd of output pulses, in each circle of operation can be altered from 1 until 10 and the duration of pause, (when the signal is maintained in the level of 0V), from 9 until 0. The waveform [1] -acquaintance as burst - it is particularly benefit for the control of instability low or high frequency circuits.

Intermittetly_pulse_generator-circuit diagram


How it works?

The circuit of generator that produces the interrupted square pulses and the produced vibrations in various points of circuit, when the selector of switch S1 is (ON), in the place 3, that correspond in exit Q3 of IC2/7. If in entry J1 we apply pulse line, width ± 5V, then these via the S2, enter in the entry of 3 IC1A that is j-k flip-flop as T, with a view to it ensures in the circuits that follow, pulses with reason of duration to period 50%. Become division of frequency pulses, via 2. Thus in the exit Q-IC1A/1, are presented pulses with submultiples frequency.

This pulses are applied in entry CLK, the IC2/14 and in a entry of IC3Α. The IC2 is one decimal counter with decode exits. Each pulse of entry makes [ H ], one from his exits and concretely the one that corresponds in the content of enumeration. In the first pulse of entry, [ H ] becomes only exit Q1, of counter, while all the other are maintained in [ L]. The second pulse of entry makes [ H ], the exit Q2, third the Q3. The tenth pulse annihilates the content counter and it makes [ H ] the exit Qo, in order to is repeated the same circle of operation for the next pulses, entering pulse line. The number of pulses that will pass to the exit of generator is checked from counter, the flip-flop IC1B, and gate IC3Α. In the particular application the logic [ H ] corresponds in + 5V and the logic [ 0 ] from the -5v. Proportionally the place that will be placed switch S1, is checked the number of pulses that will pass to the exit of generator.

In the last place of S1 (place 10), flip-flop IC1B does not make RESET, so that are presented pulses continuity in the exit of generator. In the last place of S1 (place 10), flip-flop IC1B does not make RESET, so that are presented pulses continuity in the exit of generator. The output stage of generator, gives the three different levels of level that we needed: the output positive voltage it is created by the drive of Q2, in the satiation and Q3 in the cutting off, null from the cutoff of also two transistors and negative from the control of Q2 in the cutoff and Q3 in the satiation. The signal is applied in exit J2 via the pontesometer RV1, that with the R8, gives output impedance 600R. Can we change sine wave, triangular etc, signals in square pulses with the circuit of entry, that is constituted by the gates IC3B-C-D. The choice direct or transformation, the entering signals, becomes from switch S2. Switch S1, can be also replaced from a switching switch of 10 places, good quality. The supply becomes from two batteries NiCd, but can become also from suitable power supply. The essential stabilisation of voltage, becomes from the two diodes zener.

Parts List :

Parts List


Mini Bench Supply

Every electronics engineer is familiar with the anxiety of the moment when power is first applied to a newly-built circuit, wondering whether hours of work are about to be destroyed in a puff of smoke. A high-quality power supply with an adjustable current limit function is an excellent aid to steadying the nerves. Unfortunately power supplies with good regulation performance are expensive and homebrew construction is not always straightforward. Many of the ‘laboratory power supplies’ currently on the market are low-cost units based on switching regulators which, although certainly capable of delivering high currents, have rather poor ripple performance. Large output capacitors (which, in the case of a fault, will discharge into your circuit) and voltage over-shoot are other problems.

The power supply described here is a simple unit, easily constructed from standard components. It is only suitable for small loads but otherwise has all the characteristics of its bigger brethren. Between 18 V and 24 V is applied to the input, for example from a laptop power supply. This avoids the need for an expensive transformer and accompanying smoothing. No negative supply is needed, but the output voltage is nevertheless adjustable down to 0 V.  A difficulty in the design of power supplies with current limiting is the shunt resistor needed to measure the output current, normally connected to a differential amplifier. Frequently in simple designs the amplifier is not powered from a regulated supply, which can lead to an unstable current regulation loop. This circuit avoids the difficulty by using a low-cost fixed voltage regulator to supply the feedback circuit with a stable voltage. This arrangement greatly simplifies current measurement and regulation.

Mini Bench Supply Circuit Diagram

Mini Bench-Supply-Circuit Diagram

To generate this intermediate supply volt-age we use an LM7815. Its output passes through R17, which measures the output current, to MOSFET T1 which is driven by the voltage regulation opamp IC1C. Here R11 and C4 determine the bandwidth of the control loop, preventing oscillation at high frequencies. R15 ensures that capacitive loads with low effective resistance do not make the control loop unstable. The negative feedback of AC components of the current via R12 and C5 makes the circuit reliable even with a large capacitor at its output, and negative feedback of the DC component is via the low-pass filter formed by R14 and C6. This ensures that the volt-age drop across R15 is correctly compensated for. C7 at the output provides a low impedance source for high-frequency loads, and R16 provides for the discharge of C17 when the set voltage is reduced with no load attached.

Current regulation is carried out by IC1D. Again to ensure stability, the bandwidth of the feedback loop is restricted by R19 and C8. If the voltage dropped across R17 exceeds the value set by P2, the current limit function comes into action and T2 begins to conduct. This in turn reduces the input voltage to the voltage regulation circuit until the desired current is reached. R7, R9 and C3 ensure that current regulation does not lead to output voltage over-shoots and that resonance does not occur with inductive loads.

The controls of the power supply are all voltage-based. This means, for example¸ that P1 and P2 can be replaced by digital-to-analogue converters or digital potentiometers so that the whole unit can be driven by a microcontroller. IC1B acts as a buffer to ensure that the dynamic characteristics of the circuit are not affected by the setting of P1. IC1A is used as a comparator whose out-put is used to drive two LEDs that indicate whether the supply is in voltage regulation or current regulation mode. If D2 lights the supply is in constant voltage mode; if D1 lights it is in constant current mode, for example if the output has been short-circuited. The power supply thus boasts all the features of a top-class bench supply.IC1A and its surrounding circuitry can be dispensed with if the mode indication is not wanted.

A type LM324 operational amplifier is suggested as, in contrast to many other similar devices, it operates reliably with input voltages down to 0 V. Other rail-to-rail opamps could equally well be used. The particular n-channel MOSFET devices used are not critical: a BUZ21, IRF540, IRF542 or 2SK1428 could be used for T1, for example, and a BS170 could be used in place of the 2N7002. The capacitors should all be rated for a voltage of 35 V or higher, and R15 and R17 must be at least 0.5 W types. The fixed voltage regulator and T1 must both be equipped with an adequate heatsink. If they are mounted on the same heatsink, they must be isolated from it as the tabs of the two devices are at different potentials.

Author : Alexander Mumm - Copyright : Elektor

Automatic Turn off Relay

Per request the circuit today we have relay circuit. It is worth noting again that the diagram provides a time delay of about 0.5 seconds for every microfarad in the value of capacitor C1.

Automatic Turn off Relay Circuit Diagram

Automatic-Turn off Relay-Circuit Diagram

This permits delays of up to several minutes. If desired, the delay periods can be made variable by replacing resistor R2 with a fixed and variable resistor in series whose nominal values are approximately equal of the total value of R2 (680K).

AC Switch Control with Opto-Triac

AC switches are silicon devices that control AC loads directly connected to the AC mains. This means that the driving reference terminal of the AC switch can be connected to the Line potential. This circuit explains the need of an insulation layer for the control unit and the way to implement it for an AC switch device.  It was thought in the past that connecting an MCU to the Line should be avoided as it will lead to poor appliance immunity. But it has been demonstrated over the years that such topology provides good immunity. Connecting an MCU supply to a stable non-floating reference is even better for immunity.

Safety insulation should be provided between accessible parts and high-voltage circuits to protect end users against electric shocks. It’s not required to ensure safety insulation by insulating low-voltage control circuits (like MCU) from high-voltage parts (like AC switches). In fact, the insulation could be implemented elsewhere—for example, on the keyboard to which the end user has access—leaving the MCU connected to the Line. This could be cost-effective as a non-insulated power supply and non-insulated drivers would then be sufficient.

Fig. 1: Circuit of AC switch control with opto-triac

AC Switch Control with Opto-Triac-Circuit diagram
Operational insulation is required when the control circuit reference is not the same as the AC switch reference. This is the case with new appliances using an inverter for 3-phase motor control, where the MCU is connected to the DC rail and the AC switch is referenced to Line. A level-shifter is used to allow communication between the MCU and the power switch. A usual way to implement this is to use an opto-triac but such a device will not work properly for all AC switches.

Among AC switches available today, different technologies and designs are used. The main known families are the standard triacs, the snubberless triacs and ACS devices. To switch-on a triac or an ACS device, a gate current must be applied between the gate (G) and terminal A1 for the triac, or between gate and terminal COM for the ACS device.

Fig. 2: Pin configuration of ACS108

Pin configuration of ACS108
For the triac, the gate current could be positive or negative, but the silicon structure of an ACS device is different from a triac. Here the gate is the emitter of an npn bipolar transistor. So there is only one p-n junction. The gate current can then only be sunk from the gate, not sourced to it.  As ACS de-vices can be triggered only by a negative current, an opto-triac will drive the ACS device only when the Line voltage is negative. This will lead to half-cycle conduction, which is inconvenient for most applications. However, there are new applications where such an operation is requested—for example, pumps used in coffee machines that feature an internal diode, and electromagnets used for door-lock function in washing machines.

As shown in Fig. 1, the circuit is built around ACS108 (Triac 1), opto-triac IC MOC3020 (IC1) and a few discrete components. Working of the circuit is simple. When you press switch S1, the load is switched on. When you release switch S1, the load turns off. Once the switch is pressed, the opto-triac (IC1) conducts to charge capacitor C1 up to VGT (about 0.7 volt). COM-G junction forward-biases, triggering the ACS device by a negative gate current. The ACS device will remain ‘on’ up to the next zero-current crossing point. G-COM voltage is down to –0.7V due to ACS device conduction and the capacitor remains charged. As the current through the ACS device increases, VG-COM increases and there-fore a negative current is applied by C1 which triggers the AC switch for the next cycle.

In this solution, the ACS device is ‘off’ at the beginning of each time cycle required to recharge capacitor C1. The ACS device turns ‘on’ when the voltage across its terminals equals approximately 10V. This behaviour doesn’t result in high conducted noise as the Line current is still approximately sinusoidal due to the charge current flowing through capacitor C1 at zero-voltage crossing point.

Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. The pin configuration of ACS108 is shown in Fig. 2. Fix switch S1 on the front panel, and two terminals for the load on the rear side of the cabinet.

Author : STMicroelectronics - Copyright: EFY

Momentary Action with a Wireless Switch

Many different types of wireless switch modules with a relay for switching AC power loads are commercially available. However, some applications require a short On or Off pulse, such as is provided by a momentary-action (pushbutton) switch. Here we describe a solution that simulates a pushbutton switch with a standard wireless switch. A supplementary circuit converts the switch module into a remotely controllable momentary action switch.

In the supplementary circuit, S1 is the switching contact of the relay in the wireless switch module. This contact energises a 24-V power supply connected directly to the AC power outlet, consisting of a bridge rectifier (D1–D4) with a series resistor (R1), a series capacitor (C1), and a charging capacitor (C2). The two Zener diodes in the bridge rectifier (D1 and D2) limit the DC voltage on C2 to approximately 24 V.1

Momentary Action with a Wireless Switch Schematic


When the wireless switch module closes con-tact S1, 24 VDC is applied to the coil of relay RE1, which closes. At the same time, capacitor C3 charges via D5. When the contact of RE1 switches, capacitor C4 provides the charging current for C3. The charging current flows through the coil of RE2, which remains actuated as long as the current is sufficiently large. The current decreases as the voltage on C4 rises, with the result that RE2 drops out and the contact of RE2 (the ‘momentary’ contact) opens again.

S1 opens when the relay in the wireless switch module is de-energised, which causes RE1 to drop out shortly afterward and connect capacitor C4 to ground. The capacitor discharges through the coil of RE2, causing its ‘momentary’ contact to be actuated again. The timing diagram shows the switch-on and switch-off sequences of the wireless switch (S1 contact).


The duration of the ‘button press’ (engagement time of RE2) depends on the capacitance of C3 and C4. The equation Q = C × U = I × t can be used to calculate suitable capacitor values for a specific hold time (t1in the timing diagram) with a given relay current. The value shown in the circuit diagram (1000 µF) corresponds to a hold time of 1 second with a relay current (holding current IH) of 10 mA:

C = IH× t1/ U = (0.01 A) × (1 s) / 10 V = 1000 µF.

A reed relay cannot be used for RE2 because the voltage across the coil reverses. This also means that a free-wheeling diode can-not be used, but it is anyhow not necessary due to the slow discharge of C4. RE2 should be a 'Class II' relay (such as the Omron G6D-1A-ASI 24DC) to provide adequate insulation of the switch contact. RE1 does not have to be a Class II relay. Due to the presence of AC power line voltage, R1 and R2 must have a rated working voltage of 250 V (150 V ), although they can also be formed from two resistors with half this rated working voltage connected in series, each with half of the specified power rating. In this case, R1 consists of two 47 Ω / 1 W resistors and R2 of two 100 kΩ / 0.25 W resistors. Readers on 120 VAC 60 Hz power networks should change C1 into 680 nF.

The circuit can be fitted in a plastic enclosure with an integrated AC power plug, which can easily be plugged into the wireless switch module. The contact of RE2 can then be fed out to a terminal strip as a floating contact. For adequate AC isolation, a safety clearance of at least 6 mm (air and creepage paths) to other conductors must be maintained, in addition to using a Class II relay.

OBD Vehicle Protection

Vehicle immobilisers are fitted as standard to modern cars and heavy goods vehicles. Anti-theft mechanisms have become more sophisticated but so have the methods employed by crooks. Nowadays once the thief has gained access to a vehicle they will most likely use an electronic deactivation tool which seeks to disable the immobiliser, once this has been accomplished a blank transponder key/card can be used to start the engine. In many cases communication with the immobiliser is made using the OBD-II diagnostic connector.

Although the OBD-II protocol itself does not support the immobiliser, the vehicle manufacturer is free to use the interface as neces-sary for communication, either the standard OBD-II signals or unused pins in the OBD-II connector (i.e. those undefined in the OBD-II standard). Using one of these pathways the immobiliser can usually be electronically disabled.

OBD Vehicle Protection Circuit Diagram

OBD-Vehicle-Protection-Circuit Diagram

This may be unsettling news for owners of expensive vehicles but when professional car-thieves call, armed with the latest OBD-II hacking equipment this simple low-cost low-tech solution may be all that you need. The idea is ver y simple: if all connections to the OBD-II connector are disconnected there is no possibility for any equipment, no matter how sophisticated to gain access via the vehicle’s wiring.

The OBD-II connector is usually locate d underneath the dashboard on the passenger side; once its wiring loom has been identified a switch can be inserted in line with the wires. The switch should be hidden away some-where that is not obvious. In normal opera-tion you will be protected if the vehicle is run with the wires to the socket disconnected. Make sure however that you throw the switch reconnecting the socket before you next take the vehicle along to a garage for servicing or fault diagnosis.

The diagram shows the ISO K and ISO L wires switched. To cover all bases it is wise for every wire to the socket is made switchable except the two earth connections on pins 4 and 5 and the supply voltage on pin 16. Almost ever y vehicle manufacturer has their own method of vehicle immobilisation, by disconnecting every wire it ensures that no communication is possible (even over the CAN bus). Now the innermost workings of your vehicle will be safe from prying eyes. When a hacker plugs in a deactivation tool it will power up as normal but probably report something like ‘protocol unrecognised’ when any communication with the OBD port is attempted.

Author : Florian Schäffer - Copyright: Elektor

1W Audio Amplifier Circuit Using NCP2830

This 1w audio amplifier circuit is designed using NCP2830 audio IC manufactured by ON Semiconductor. This audio power amplifier ic designed for portable communication device applications and require few external electronic components.
1W Audio Amplifier Circuit Diagram
1W-Audio Amplifier-Circuit Diagram
NCP2830 is capable to provide 1W continuous output power in 8 ohms load. NCP2830 audio power amplifier main features are : high quality audio (THD+N = 0.04%) , low noise: SNR up to 100 dB, overall system efficiency optimization: up to 89% , Superior PSRR (−88 dB): Direct Connection to Battery , Very Low Quiescent Current 7 mA , Optimized PWM Output Stage: Filterless Capability , Selectable gain of 2 V/V or 4 V/V .

Voltage Limiter for Guitar Amplifiers

Guitar amplifiers using output devices such as the TDA7293 (100 W) or LM3886 (68 W) are surprisingly of ten damaged as a result of excessive supply voltage in the quiescent state. The transformers are of ten used so close to their specification that this problem can even be caused by a high mains input voltage. In most countries the domestic AC outlet voltage is permitted to rise as high 10 % above the nominal (published) value. Since replacing the transformer is not an attractive proposition, the author developed a relatively simple electronic solution to the overvoltage problem: a voltage limiter for the symmetric supply to the amplifier.
The circuit is based on the classical voltage regulator arrangement of a Zener diode connected to the base of a pass transistor. However, in this version we replace the conventional bipolar transistor with a power MOSFET.The circuit is symmetrical with respect to the negative and positive supplies, and so we shall only describe the positive half.
Voltage Limiter for Guitar Amplifiers Circuit Diagram
Voltage-Limiter-for-Guitar-Amplifiers-Circuit diagram
The input voltage (at most 50 V) supplies the chain of Zener diodes D1, D2 and D3 via resistor R3. The resistor limits the current through the Zener diodes to about 5 mA. The series connection of Zener diodes has the advantage that their dissipation is divided among them, as well as giving more options for the total voltage drop by judicious selection of individual components. The sum of the diode voltages (39 V with the values given) must be greater than the desired limiting out-put voltage by the gate-source voltage of the MOSFET. C1 smooths the voltage across the Zener diode chain. The circuit therefore not only limits the voltage, but also reduces the ripple (hum component) on the supply. The gate of the HEXFET is driven via R1. In con-junction with C4, this prevents the FET from oscillating.
Without any load the output voltage is rather higher than expected. With a small load, such as that presented by the output stage in its quiescent state, it falls to the desired value. The circuit then does not provide regulation of the output voltage, but rather a stabilisation function.The operation of the negative half of the circuit is identical to that of the positive half apart from the polarity of the voltages, and hence a P-channel MOSFE T must be used there.
It is worth noting that there is a relatively large degree of variation (up to a few volts) in the gate-source voltage of the HE XFETs used. This can be compensated for by selecting the Zener diodes in the chain and the cur-rent through them, but for most applications the exact voltage at which limiting begins to occur will not be critical.
The HEXFETs must be provided with adequate cooling. If possible, they can be attached to the heatsink already present in the amplifier; other wise, a separate heatsink will be required. A thermal rating of 2.5 K/W will be suitable.
Author :Alfred Rosenkränze - Copyright: Elektor

Automatic Mooring Light

Integrated-circuit U1-an LF351 or 741 op amp-is used as a comparator to control the light. Resistors R2 and R3 provide a reference voltage of about 2.5 volts at pin 3 of U1. When daylight falls on light-dependent resistor LDR1, its resistance is low: about 1000 ohms. In darkness, the LDR's resistance rises to about 1 megohm.

Automatic Mooring Light Circuit Diagram

Automatic-Mooring Light-Circuit Diagram

Since R1 is 100,000 ohms, and the LDR in daylight is 1000 ohms, the voltage ratio is 100 to 1; the voltage drop across the LDR is less than the 2.5 volt reference voltage and pin 2 of U1 is held at that voltage. In that state, the output at pin 6 of U1 is positive at about 4.5 volts, a value that reverse-biases Q1 to cutoff, which in turn holds Q2 in cutoff, thereby keeping lamp I1 off.  

When darkness falls, the LDR's resistance rises above R1's value and the voltage at pin 2 of U1 rises above the reference voltage of 2.5 volts. U1's output terminal (pin 6) falls to less than a volt and Q1 is biased on. The base-to-emitter current flow turns Q2 on, which causes current to flow through the lamp. When daylight arrives, the LDR's resistance falls sharply, which causes the lamp to be turned off, ready to repeat the next night/day cycle.

1 Minute to 2 Hour Timer Using IC 4060

Free circuit dot com presents the timer circuit with IC 4060 as this circuit is simple to make the project or devices.

This timer circuit can  set time at 1 minute to 2 hours.

Frist information, Technically, the IC 4060 is a 14-stage ripple carry binary counter, the oscillator and divider of a monolithic integrated circuit, contained in a 16-pin dual-in-line housing with ceramic or plastic. A phase of the integrated oscillator is a key feature of the integrated circuit, which keeps the number of components in the integrated circuit to a minimum at the design frequency generators or oscillators. The phase of the internal oscillator operation easily through a network of resistors and a capacitor connected to the pins #8, #9 and #10.

1 Minute to 2 Hour Timer Circuit Diagram

1 Minute to 2 Hour Timer-Circuit Diagram

The timer time is determined by P1 and C1, through the following formula (seconds): t = 2.3 * (P1 + 18k) * C1 * 2 ^ 13 .

The basic structure of the IC can be understood from the following:

According to the rules of standard CMOS ICs, all entries are first captured by assigning them to specific business logic or simply a voltage (not exceeding the level of supply voltage). For integrated circuit pin # 9, 10, 11 and 12 are active inputs.  Resistance to pin No. 11 can be considered a type of terminal or the reference resistance value that ideally should be 10 times more than the resistor connected to the pin 10 (the combined value of the resistor and pot fixed series).

The capacitor connected to pin # 9 is, in general, non-polar type.

No Pin 12 is the reset input of the IC on the ground must be connected so that the IC function (swing). This entry positive stop immediately IC to oscillate and return it to its original state. Set the pen is connected to the ground of the integrated circuit for counting (oscillate) for some time (for example, 1 minute), the connecting pin to the positive terminal and to immediately stop the count reset to zero.

The rest of the pin-out, the outputs of the IC that generate oscillations specific speeds. Costs are expressed in multiples of two for the entire chain pinouts as shown in the diagram. Pin # 3 indicates the lowest frequency, the highest or pulses at time intervals while the spindle 7 with the highest frequency or pulses having the lowest time intervals.

Electronic Temperature Controlled Relay

This temperature controlled relay circuit is a simple yet highly accurate thermal control circuit which can be used in applications where automatic temperature control is needed. The circuit switches a miniature relay ON or OFF according to the temperature detected by the single chip temperature sensor LM35DZ.

When the LM35DZ detects a temperature higher than the preset level (set by VR1), the relay is actuated. When the temperature falls below the preset temperature, relay is de-energized. The circuit can be powered by any DC 12V supply or battery (100mA min.)

Electronic Temperature-Controlled Relay Schematic


How it works?
The heart of the circuit is the LM35DZ temperature sensor which is factory-calibrated in the Celsius (or Centigrade) scale with a linear Degree->Volt conversion function. The output voltage (at pin 2) changes linearly with temperature from 0V (0oC) to 1000mV (100oC).

The preset (VR1) & resistor (R3) from a variable voltage divider which sets a reference voltage (Vref) form 0V ~ 1.62V. The op-amp (A2) buffers the reference voltage so as to avoid loading the divider network (VR1 & R3). The comparator (A1) compares the reference voltage Vref (set by VR1) with the output voltage of LM35DZ and decides whether to energize or de-energize the relay (LED1 ON or OFF respectively).

Components list:

IC1 : LM35DZ
IC2 : TL431
IC3 : LM358

LED1 – 3mm or 5mm LED

Q1 – General purpose PNP transistor ( A1015,…) with E-C-B pin-out)
D1, D2 — 1N4148
D3, D4 — 1N400x (x=2,,,,.7)

ZD1 — Zener diode, 13V, 400mW

Preset (trim pot) : 2.2K (Temperature set point)
R1 – 10K
R2 – 4.7M
R3 – 1.2K
R4 – 1K
R5 – 1K
R6 – 33Ω

C1 – 0.1 µF ceramic or mylar cap
C2 – 470 µF or 680 µF electrolytic cap. (16V min)
Miniature relay – DC12V DPDT, Coil = 400 Ω or higher

5v DC Converter Circuit Using LTM8031

Using LTM8031 integrated circuit, manufactured by linear technology, can be designed a very simple high efficiency dc dc converter circuit.  This LMT8031 dc voltage converter circuit will provide a 5 volts output from a wide input voltage range between 7 and 36V dc. The switching frequency range of LTM8031 is from 200kHz to 2.4MHz which can be set by a single resistor.

5v DC Converter Circuit Diagram

5v DC Converter-Circuit Diagram

To finish the design of the LTM8031 are needed only the bulk input and output filter capacitors . Main features of this ic based dc converter project are: Complete Step-Down Switch Mode Power Supply , Wide Input Voltage Range: 3.6V to 36V , 1A Output Current , 0.8V to 10V Output Voltage , Switching Frequency from 200kHz to 2.4MHz , EN55022 Class B Compliant , Current Mode Control. Maximum output current of this circuit is around 1A.

Motorcycle Battery Charger

Ordinary car battery chargers are simple and inexpensive devices that continuously charge the battery with a pace few amps, for the time the device is ON. If the holder does not close in time the charger, the battery will overcharge and electrowinning capacity will be lost by evaporation or likely to be destroyed elements. The charger circuit overcomes these defects. Electronically controls the battery charge and has a feedback control circuit, causing the battery to charge a maximum rate until fully charged. When fully charged, lights up a red Led (LD2).

The charger is designed to charge batteries of 12V, only. What should be paid by whom built the circuit, are the cables connecting the transformer to the circuit and then the battery should be high profile, so that heat when it passes through the current load and also not cause voltage drop in the path of current through them.

Motorcycle Battery Charger Circuit Diagram

motorcycle-battery-charger-circuit diagram

When construction is finished turn the TR1 in place zero value, then the following settings-control.

  1. Check without connecting the battery, that both LED’s light up.
  2. Connect a car battery charger. Check that the LD2 is off and that a current (typically 2 until 4 A), flows to the battery.
  3. Turn the TR1 and check that the LD2 can turn and charge current to cut
  4. Turn the TR1 to null value and charge the battery using the standard technique hydrometer (if not available, use a battery in good condition and fully charged).

Turn carefully so that the TR1 LD2 begins to turn and charge current drops to a few hundred mA. If TR1 installed correctly then the next load will see the first LD2 will start to flicker, and charging the battery. When fully charged the battery then the LD2 will turn on fully.

To TR1 no longer needs another adjustment. The Q1 is connected in series with the circuit of the battery and can be fired from the circuit R3-4 and LD2. The battery terminal voltage is obtained from the circuit R2, C1, TR1, D2 and activates the Q2 when the voltage terminals exceeds the value we are striving to TR1.

When an uncharged battery put on charge the terminal voltage is low. under this situation the Q2 turn off and Q1, fired in each half cycle of the circuit R3-4, LD2. The Q1 functions as a simple rectifier. While charging the battery, the terminal voltage increases. If the terminal voltage rises above the level that we have set to TR1, then shifts the Q2 gate drive of Q1, it turns off, stop giving power to the battery and lights LD2, showing us that the loading is complete. The Q1 and the bridge rectifier GR1, should be placed on a good heatsink for proper cooling. The M1 is an ammeter DC 5A, so we can monitor the charging current. Optionally can be placed a voltmeter in parallel with the poles of the battery should have high input impedance, however, not affect the circuit measuring device.

Telephone Ringtone Generator

This is a simple home telephone ringtone generator circuit which is built with applying only several electronic components / parts. It generates simulated telephone ringtone and requires only DC supply with 4.5V DC to 12V DC voltage.

One may possibly use this circuit in ordinary intercom or phone-type intercom. The sound is pretty loud when this circuit is operated on +12V DC power supply. Even so, the volume of ring sound can be adjusted.

Telephone Ringtone Generator Circuit Diagram

Ringtone generator circuit diagram

CD4060B is chosen to produce three kinds of pulses. Preset VR1 is fine-tuned to get 0.3125Hz pulses at pin 3 of IC1. At the same time, pulses obtainable from pin 1 will be of 1.25 Hz and 20 Hz at pin 14. The three output pins of IC1 are connected to base terminals of transistors T1, T2, and T3 through resistors R1, R2, and R3, respectively.

Working with a built-in oscillator-type piezobuzzer generates about 1kHz tone. In this particular circuit, the piezo-buzzer is turned ‘on’ and ‘off’ at 20 Hz for ring tone sound by transistor T3. 20Hz pulses are obtainable at the collector of transistor T3 for 0.4-second duration. Just after a time interval of 0.4 second, 20Hz pulses become again obtainable for another 0.4-second duration. This is followed by two seconds of nosound interval. Thereafter the pulse pattern repeats by itself.

Voltage Inverter using IC NE555

In many circuits we need to generate an internal adjustable voltage. This circuit shows how it is possible to use a trusty old NE555 timer IC and a bit of external circuitry to create a voltage inverter and doubler. The input voltage to be doubled is fed in at connector K1. To generate the stepped-up output at connector K2 the timer IC drives a two-stage inverting charge pump circuit.

The NE555 is configured as an astable multivibrator and produces a rectangular wave at its output, with variable mark-space ratio and variable frequency. This results in timing capacitor C3 (see circuit diagram) being alternately charged and discharged; the voltage at pin 2 (THR) of the NE555 swings between one-third of the supply voltage and two-thirds of the supply voltage.

Voltage Inverter Circuit Using IC NE555

The output of the NE555 is connected to two voltage inverters. The first inverter comprises C1, C2, D1 and D2. These components convert the rectangular wave signal into a nega-tive DC level at the upper pin of K2. The second inverter, comprising C4, C5, D3 and D4, is also driven from the output of IC1, but uses the negative output voltage present on diode D3 as its reference potential. The consequence is that at the lower pin of output connector K2 we obtain a negative volt-age double that on the upper pin.

Now let us look at the voltage feedback arrangement, which lets us adjust this doubled negative output voltage down to the level we want. The NE555 has a control voltage input on pin 5 (CV). Normally the voltage level on this pin is maintained at two-thirds of the supply voltage by internal circuitry. The voltage provides a reference for one of the comparators inside the device. If the reference voltage on the CV pin is raised towards the supply voltage by an external circuit, the timing capacitor C3 in the astable multivibrator will take longer to charge and to discharge. As a result the frequency of the rectangle wave output from IC1 will fall, and its mark-space ratio will also fall.

The source for the CV reference voltage in this circuit is the base-emitter junction of PNP transistor T1. If the base volt-age of T1 is approximately 500 mV lower than its emitter voltage, T1 will start to conduct and thus pull the voltage on the CV pin towards the positive supply.

In the feedback path NPN transistor T2 has the function of a voltage level shifter, being wired in common-base configuration. The threshold is set by the resistance of the feedback chain comprising resistor R3 and potentiometer P1. When the emitter voltage of transistor T2 is more than approximately 500 mV lower than its base voltage it will start to conduct. Its collector then acts as a current sink. Potentiometer P1 can be used to adjust the sensitivity of the negative feedback circuit and hence the final output voltage level.Using T1 as a voltage reference means that the circuit will adjust itself to compensate not only for changes in load at K2, but also for changes in the input supply voltage. If K2 is disconnected from the load the desired output voltage will be maintained, with the oscillation frequency falling to around 150 Hz.

A particular feature of this circuit is the somewhat unconventional way that the NE555’s discharge pin (pin 7) is connected to its output (pin 3). To understand how this trick works we need to inspect the innards of the IC. Both pins are outputs, driven by internal transistors with bases both connected (via separate base resistors) to the emitter of a further transistor. The collectors of the output transistors are thus isolated from one another [1].

The external wiring connecting pins 3 and 7 together means that the two transistors are operating in parallel: this roughly doubles the current that can be switched to ground.The two oscilloscope traces show how the output voltage behaves under different circumstances. The left-hand figure shows the behaviour of the circuit with an input voltage of 9 V and a resistive load of 470 Ω connected to the lower pin of output connector K2. The figure on the right shows the situation with an input voltage of 10 V and a load of 1 kΩ on the lower pin of output connector K2. The pulse width and frequency of the rectangle wave at the output of IC1 are automatically adjusted to compensate for the differing conditions by the feedback mechanism built around T1 and T2.

Because of the voltage drops across the Darlington out-put stage in the IC (2.5 V maximum) and the four diodes (700 mV each) the circuit achieves an efficiency at full load (470 Ω between the output and ground) of approximately 50 %; at lower loads (1 kΩ) the efficiency is about 65 %.

Author : Peter Krueger -  Copyright : Elektor

Simple Real Time Clock Using the PIC16CXXX

A very simple real time clock electronic project can be designed using the PIC16CXXX microcontroller family , designed by Microchip Technology . This real time clock electronic project uses the Timer1 module, from a mid-range PIC16CXXX microcontroller, to control a low-power real-time clock. Timer1 was chosen because it has its own crystal which allows the module to operate during sleep.

Upon power-up, the device is initialized with the display starting at 12:00 PM, and Timer1 is configured to generate an interrupt (every second). The Timer1 overflow interrupt wakes the device from sleep. This causes the time registers (HRS, MIN, SECS) to be updated. If the SECS register contains an even value (SECS<0> = 0), the colon (":") is not displayed. This gives a visual indication for each second. Then the device returns to sleep.

Real Time Clock Circuit Diagram

For setting the clock are used three keys : SELECT_UNITS Key (S1) selects which units are to be modified (hours, minutes, off), the INC Key (S2) increments the selected units and CLR_MIN Key (S3) clears the minutes and seconds (useful for exactly setting the time ) .

This simplify design use a standard Hitachi LCD display module and some other electronic parts .

The RA2:RA0 pins are the control signals to the LCD display, RB3:RB0 acts as a 4-bit data bus, and RB7:RB5 are the input switches. The OSC1 pin is connected to an RC network, which generates an approximate 4 MHz device frequency. Because Timer1 operates asynchronously to the device, the device's oscillator can be configured for RC mode.

Timer1’s crystal is connected to the T1OSI and T1OSO pins. A good choice for a crystal is a 32.786 kHz (watch) crystal.

This electronic project and source code was designed by Mark Palmer Microchip Technology Inc. Download Source code

12-9 Volt DC to DC Converter BD139

This circuit is a DC voltage output from a small DC input generate large voltage.It ‘s easy and quick to do, and reducing the value of the Z-diode, the circuit can be universally adapted to other output devices of the circuit voltages. The give and all diagrams represent a DC converter with 12V battery 9 volt DC input and output.
12-9 Volt DC to DC Converter Circuit Diagram

With the 10V zener diode, as in the diagram, the output voltage is approximately 9.3 volts DC. The supply voltage is used, should always be at least a few volts higher than the Zener voltage. In this example, I have a 12 Volt DC battery to provide regulated 9-volt DC output.

Power LED Driver

If you want to operate power LEDS with a truly constant current which significantly prolongs the lifetime of the lamp and avoid the power loss resulting from using a constant voltage supply with a series resistor, you need a suit-able constant current source. However, the only way to achieve really good efficiency is to use a switching regulator. Altogether, this means that you need a switching regulator designed to generate a constant current instead of a constant voltage.

With this in mind, the author started working on the development of a LED pocket torch with especially high efficiency. Along with using high-capacity rechargeable batteries to maximise operating life, it’s worthwhile to be able to reduce the brightness, and therefore the operating current of the LEDs, when you don’t need full power. Accordingly, the author incorporated a dimming function in the design, based on operation in PWM mode in to reduce power losses to an absolute minimum.

Power LED Driver Circuit Diagram
As you can see from the circuit diagram, the author chose an LT3518 switching regulator IC, which is a buck/boost converter optimised for LED operation. Here it is used as a down converter (buck mode). This IC can achieve better than 90% efficiency in this mode, depending on the input voltage. According to the typical application circuit on the data sheet [1], its switching frequency can be set to approximately 170 kHz by selecting a value of 82 kΩ for R1. To maximise overall efficiency with this type of IC, the volt-age drop over the sense resistor used to measure the current flowing through the LED should be as low as possible. This particular device operates with a voltage drop of 100 mV, corresponding to a current of just under 1.5 A with the specified value of 68 mΩ for R2. This value proved to be suitable for the Cree LED used by the author. At this current level, a diode with a power rating of at least 6 W should be used for D1.

IC1 has an additional property that is ideal for this application: the connect-ed LED can be dimmed by applying a PWM signal to pin 7 of the IC, with the brightness depending on the duty cycle. Obviously, the PWM frequency must be lower than the switching frequency. The PWM signal is provided by IC2, a special voltage-controlled PWM generator (type LTC6992 [2]). The duty cycle is controlled by the volt-age applied to the MOD input on pin1 (range 0–1 V). The resistor connected to pin 3 determines the internal clock frequency of the IC according to the formula f= 1 MHz × (50 kΩ/R3). This yields a frequency of approximately 73.5 kHz with R3 set to 680 kΩ, which is much too high for controlling IC1.

However, the PWM IC has an internal frequency divider with a division factor controlled by the voltage applied to pin 4, which in this circuit is taken from voltage divider R4/R5. The division factor can be adjusted over the range of 1 to 16,384. The division factor with the specified component values is 64, resulting in a PWM frequency of around 1,150 Hz. If you want to be able to generate a PWM signal with an adjust-able duty cycle over the full range of 0 to 100%, you must use the LTC6992-1 option. The -4 option, which provides a range from 5 to 100%, might be an acceptable alternative.To prevent the duty cycle (and thus the brightness of the LED) from depending on the battery voltage, which gradually drops as the battery discharges, IC3 generates a stabilised 1.24 V control voltage for potentiometer P1. Series resistor R7 reduces the voltage over P1 to 1V, which exactly matches the input voltage range of the LTC6992.

All capacitors should preferably be ceramic types, in particular due to their low effective series resistance (ESR) as well as other favourable characteristics. However, only capacitors with X5R or X7R dielectric should be used; capacitors with type Y dielectric have very poor temperature characteristics.The supply voltage is limited to 5.5V by the maximum rated supply voltage of IC2. The author used four NiMH re-chargeable cells connected in series, which yields a voltage that is just within spec. With an operating voltage in the range of 4.5 V to 5.5 V, you must use an LED that can operate at less than 4V.

This eliminates devices with several chips connected in series on a carrier, which is very often the case with power LEDS rated at over 5 W. These devices require a correspondingly higher supply voltage, which means more cells connected in series. This is only possible if the supply voltage for IC2 is reduced by a 5 V voltage regulator or other means, and of course R4 must also be connected to this lower supply voltage.

Finally, a few words about soldering. An exposed thermal pad must be provided on the PCB for the LT3518, and the rear face of the IC must be soldered to this pad. The author obtained good results by dimensioning the exposed pad large enough to extend beyond the outline of the IC. When assembling the board, first tin the pad and the rear face of the IC. Then heat the pad with a soldering iron. When the solder melts, withdraw the tip of the soldering iron to the edge of the pad and simultaneously place the IC on the pad and align it. After this the pins can be soldered.

Author : Burkhard Kainka Copyright: Elektor

Electronic Car Horn

An LM556 dual oscillator/timer, U1, configured as a two-tone oscillator drives U2, a dual 4-watt amplifier. One of the oscillators, pins 1 to 6, contained in U1 produces the upper frequency signal of about 200 Hz, while the second oscillator, pins 8 to 13, provides the lower frequency signal of about 140Hz.

Electronic Car Horn Circuit Diagram

Increase or decrease the frequencies by changing the values of C2 and C3. U1's outputs, pins 9 and 5, are connected to separate potentiometers to provide control over volume and balance. Each half of U2 produces 4W of audio that is delivered to two 8 ohms loudspeakers via capacitors C7 and C8.

12V Step-Down Dc Converter Using ADP2300 ADP2301

Using ADP2300 ADP2301 step-down dc dc regulators with integrated power MOSFET, can be designed a very simple DC DC voltage converter. Output voltage delivered by these circuits can be adjusted from 0.8 volts, up to 0.85xVin , with ±2% accuracy. The maximum output current that can be provided by ADP2300 ADP2301 regulators is up to 1.2 A load current.

12V Step-Down Dc Converter Circuit Diagram

12V Step-Down Dc-Converter-Circuit Diagram

12V Step-Down Dc-Converter-ADP2301
There are two frequency options: the ADP2300 runs at 700 kHz, and the ADP2301 runs at 1.4 MHz. These options allow users to make decisions based on the trade-off between efficiency and total solution size. Current-mode control provides fast and stable line and load transient performance.  Bellow you an see two design examples, which require few common electronic components.First circuit will provide a 2.5V output at a maximum current of 1.2A from an input voltage of 12 volts. Second circuit will provide a 5V output at a maximum current of 1.2A from an input voltage of 12 volts.

Short-Circuit Protection with a MOSFET

If you have an application in which a MOSFET is already used to switch a load, it is relatively easy to add short-circuit or overload protection. Here we make use of the internal resistance R DS(ON), which produces a voltage drop that depends on the amount of current flowing through the MOSFET. The voltage across the internal resistance can be sensed using simple comparator or even a transistor, which switches on at a voltage of around 0.5 V. You can thus avoid the use of a sense resistor (shunt), which usually produces an undesirable extra voltage drop.

Short-Circuit Protection Circuit Diagram

Short-Circuit-Protection-Circuit Diagram

The comparator can be monitored by a microcontroller. In case of an overload, the software can initiate suitable countermeasures (PWM regulation, alarm, emergency stop etc.). It is also conceivable to connect the comparator out-put directly to the gate of the MOSFET, in order to immediately cut off the transistor in case of a short circuit.

FM Stereo Transmitter

You'll find that this is a very easy project to build. It will transmit good quality sound in the FM band ( 88 - 108 mhz ). One inportant item is that the IC chip operates on 3 volts DC. The chip will get destroyed if it is operated on any voltage higher than 3.5 volts. The antenna can be a standard telescopic antenna or a 2 foot length of wire. The input is in the millivolt range and you may need to add additional pots for the inputs. I was able to use this circuit for a walkman and a portable CD player in my car. I used the headphone jack on both and varied the signal with the volume control.

FM Stereo Transmitter Circuit Diagram

FM Stereo-Transmitter-Circuit Diagram

To adjust the circuit tune your FM radio to a quite spot then adjust the trimmer capacitor C8 until you hear the signal that you are transmiting. When you have a strong signal adjust the resistor R4 until the stereo signal indicator lights. If the input is to high of a signal you may over drive the IC chip. Use two 15 turn pots on the input signals to bring the level down. You can balance the signal by using headphones. The inductor L1 is 3 turns of .5 mm wire on a 5 mm ferrite core.

Pump Protector Schematic

This circuit has been developed to limit the running time of a sump pump, since the pump can be damaged if it runs too long when the sump is dry. The circuit detects how long the pump has been switched on, and if this time exceeds a previously set limit (30 minutes in this case), the supply voltage to the pump is interrupted.

The protector circuit is connected in series with the pump’s mains supply cable. The 230-V input is on the left-hand side of the schematic diagram, and the output is on the right. The schematic diagram consists of three main elements: the power supply, the timing circuit and the in-use detector.  The supply voltage is taken from the mains connection to the pump via transformer Tr1. Since voltage stabilisation is not necessary, the power supply can be limited to the standard combination of a transformer, a bridge rectifier and a smoothing capacitor. LED D5 acts as an on/off indicator. A 4060 (IC1) is used for the timing function. LED D10(Count) blinks as long as power is supplied to the load.Output Q14 of IC1 goes High after 30 minutes. Alternatively,the Test jumper position can be used to select output Q6.  This output interrupts the power to the pump after 6 seconds for testing purposes.

Pump Protector Schematic Circuit Diagram

Pump Protector-Schematic-Circuit Diagram

Two diodes connected anti-parallel (D6–D7) are placed in series with one of the supply leads to detect whether the pump is running. When the pump switches on, the voltage drop across these diodes is sufficient to cause T1 and T2 to conduct. These transistors pull down the Reset input of IC1, so the timing circuit starts to count. Diodes D8 and D9 provide a return path to ground from the Reset pin; a direct connection at this point would short out the detection diodes, which is not what we want! These diodes cause the Reset level to lie at around 0.8 V. Capacitor C2 suppresses the crossover spikes from the ac signal, which could otherwise cause the circuit to malfunction.

If the pump is still running when the time interval has expired, T3 energises the 12-V relay Re1, which in turn drives a 220-V relay with two changeover contacts. One of these contacts interrupts the supply voltage to the pump, while the other one is used to activate the Reset LED (D11). The pump can be started again by pressing the Restart button.

We can conclude with some practical remarks. First, a Euro card relay relay may be used for Re1, and second, the Reset pushbutton switch must naturally be a normally-closed 230-V type. Finally, since the entire circuit is connected to the mains network, full consideration must be given to electrical safety in its construction, and a well-insulated enclosure is mandatory.

90Watts Amplifier Using Transistors

Using some power transistors and some other common electronic components, can be designed a high power audio amplifier capable to provide a maximum output power of 90W. This power amplifier based on transistors is capable of provide an output of 70W on a load of 8 ohms or 90W on a 4 ohms load. If the component values in parentheses are used can be connected speakers with 4 ohm impedance, in which case the amplifier maximum output power will be around 90 watts.

90Watts Amplifier Using Transistors Circuit Diagram

Amplifier Using-Transistors-Circuit Diagram
The input signal is brought to the transistor T1 and the reaction is taken on the basis of T2. Current through deferential stage is kept constant at 1 mA current source through the action of T3. The input signal for T4/T8 transistor is taken from the T1's collector in combination with current source T5 forms a control stage class A for power transistors. Current through control stage is quite small (about 7 mA) as T6 and T9 are Darlington power transistors.

Protection circuit from Fig. 2 must also be changed when using a 4 ohm load. R24 and R28 values are then 3k9, R26 and R28 are 220 ohms, and D5, D6 and R30 are all eliminated. Rectified voltage for 70 W / 8 ohms version is ± 40 V to be in load, no load, this corresponds to about ± 47 V. At 4 ohms, these values are ± 34, respectively, ± 40 V. The transformer used must provide for alternative 1A 70 W / 8 ohm (mono) and 2.2 A for version 90 W / 4 ohms.

Sound Effects Generator 2

This circuit uses the Holtek HT2884 IC to produce 8 different sound effects. All sound effects are generated internally by the HT2884 IC. Power is a 3 Volt battery, but the IC will work with any voltage between 2.5 and 5 Volts. Switch S1 is the on / off switch.

Sound Effects Generator 2 Circuit Diagram:

Sound Effects-Generator-2-Circuit Diagram

The output at pin 10 is amplified and drives a small 8 ohm loudspeaker. Pressing S3 once will generate all the sounds, one after another. S2 can be used to produce a single sound effect, next depression gives the next sound effect. There are 2 lazer guns, 1 dual tone horn sound, 2 bomb sounds, 2 machine gun sounds and a rifle shot sound. Standby current is about 1 uA at 3 Volt, so battery life is very economical. The IC may be obtained from Maplin Electronics order code AZ52G.Link

Tent Alarm

Although this alarm is designed to protect valuables left in a tent, it can also be used as a baggage alarm (either on or in one‘s bags) and in similar situations.

The tent alarm can be triggered by many different sensors. One is a current loop, connected to pin PB4 of an ATtiny13 micro-controller: this could be a thin wire which would be broken by a prospective pilferer caught off his guard. Alternatively, it can be a reed switch contact normally held closed by a magnet, arranged so that the budding burglar will accidentally move the magnet and thus open the contact. This could be used to protect a door or a zip fastener securing a tent.

Another sensor connected to PB4 is an LDR (light dependent resistor). If the LDR is left in a dark place (such as under a sleeping bag) the thief will trigger the alarm if he moves the bag to expose the sensor to light. The resistance of the LDR is about 100 kΩ in the dark and just a few ohms in the light. If only the light sensor is to be used, the alarm wire (or reed contact) socket can be shorted using a jumper. If the LDR is not to be used, it can either be (temporarily) taped over to exclude light from it or (more permanently) replaced by a 100 kΩ resistor.

Tent Alarm Circuit Diagram:

Tent Alarm Circuit Diagram

A third sensor which can trigger the alarm is a vibration detector (S6), which is wired in series with a tilt sensor. The tilt sensor allows the vibration sensor to be disabled when the alarm unit is left upside-down. When the tilt sensor contacts are open, PB1 cannot be pulled low and so no alarm can be triggered.

The unit also features a number of push-buttons and switches connected to PB2. The arrangement and labelling of these buttons and switches is described below.On the left of the device lies switch S1 with the (deliberately misleading) legend ‘Power on/off ’. Of course, this does not turn the alarm on and off. On the right of the device is switch S2 with the legend ‘Speaker on/off ’, which, naturally, does nothing of the sort. As you have probably already guessed, the red and green but-tons also have nothing to do with arming or disarming the alarm.

These decoys should be enough to annoy and delay all but the most resourceful of robbers. Naturally, once the alarm has been triggered by uncovering the LDR, it will not turn off again if the LDR is then covered.The only way to disable the alarm is to set S1 and S2 in the correct positions (namely, ‘Power on’ and ‘Speaker on’) and hold down the two buttons simultaneously for five seconds. More complicated deactivation procedures can be programmed into the software, in case you are worried that some light-fingered Elektor reader (not that such a person exists) will be able to steal your valuables after having seen this article.The circuit requires a supply voltage of between 3.6 V and 5 V. In the circuit diagram we show a power supply made using a 9 V battery and a 5 V voltage regulator.

The ATtiny13 microcontroller belongs to Atmel’s AVR family, and can be programmed using BASCOM. Source and object code files, including fuse settings, are available in a ZIP archive that is available for free download from the Elektor website. The source code can be modified to suit your own application and then recompiled using the free version of BASCOM. The software arranges matters so that the processor enters sleep or power-down mode when the alarm is correctly deactivated; there is no other way to turn the device off. To wake the device up the switches must be set correctly (both to ‘on’) and the unit shaken briefly. The LED blinks twice to con-firm that the device has woken up; after a brief delay of approximately three seconds the alarm is armed. This state is indicated by three flashes of the LED. While the alarm remains in the armed state the LED blinks briefly once every few seconds.

When the alarm is triggered the red LED lights immediately. If it is not disarmed, the alarm sounds after a short pause.

To disarm the unit, both switches again need to be in the ‘on’ position as described above and both buttons must be pressed. After a double flash, whether the LED is on or off indicates whether the buttons must then be pressed again or not.

Author :Stefan Hoffmann - Copyright: Elektor

Infrared Emitter and Detector using IC 74LS14

This circuit have applied to line detection of robot project, Good match between the transmitter and the detector is important for proper operation, especially if the hole is large. Robot with a simple object or obstacle detection. Infrared Transmitter detector pair sensors are relatively easy to implement, although involved some degree of testing and calibration in order to make correct. They can for the impediment, motion detection, transmitters, encoders are used, and the color detection.

Infrared Emitter and Detector using IC 74LS14 Circuit Diagram:


This can be done with a piece of rope stretched between and in accordance with LED and phototransistor. A length of stiff wire or plugs can be used to set the alignment. Another method that can be used for long distances is a laser pointer shone through a hole.

Automatic Wiper Control

A continuously working wiper is a big problem when it is raining slightly.The wiper control given here makes the wiper to sweep at rates from 1S to 10 S.

The circuit is build around an astable multivibrator using NE 555.Here the output at pin 3 remains high for a time period set by R2 ,and low for a time period set by R3.The low output pulse drives the transistor pair to drive the wiper motor to make one sweeping cycle and waits for next low pulse to arrive for next sweep.The high going pulse at pin 3 determines how many time should wiper should sweep in a given period of time.

Automatic Wiper Control Circuit Diagram:



  • Connect the circuit to 12V line from Vehicle and connect the wiper motor and wiper switch as shown in figure.
  • For setting the device first find out how much time it is required for the wiper to complete one sweep cycle.Now adjust
  • R3 such that wiper makes correct one sweep cycle.Fix R2 some where on the dash board.And now the system is ready to use.
  • You can adjust the sweep rate of the wiper using R2 according to the intensity of rain.

Source : Circuits today

Thermostat using with LM319

This first circuit is designed by me to replace the mechanical switches used in some thermal Electric I have heaters.The electrical contacts to these mechanical thermal switches are always stoned and “no longer be trusted.”They could easily be welded together, the maintenance of these heating on full. It is definitely not good! Coarse adjustment of the temperature is a trimmer on the track, set to give a nominal range When using the fine adjustment.

It is quite difficult in a D-53, manufactured by NEC. The plumb line that is not isolated to the body of the thermistor is arranged. Why is it when you use the wire must be insulated to withstand the high temperatures such as fiberglass insulation against pipe.

Thermostat  Circuit Diagram:

Thermostat using with LM319-circuit-diagram

What is the size of the thermistor is the disk diameter 7 mm and a thickness of 2 mm. The end temperature control is a standard isolated potentiometer with a knob and / or good Protection against electric shock. Harter can be adjusted with this controller Auto-On and Off, “which automatically adjusts the room temperature.

The power control for the triac should be a 2 watt potentiometer with a knob isolated and / or Tree for protection against electric shock.  It can also be set up a 2-watt resistor on the circuit, an appropriate level of heat.“In general, full on,” how would the “Normal” setting when you use the contacts.On the chart, show me a 10 Meg resistance hysteresis. This may be of Lower Austria or higherdepending on how many degrees of difference between you and off cycles.Values between 100 K-ohms and 22 ohms, Meg are acceptable.

Simple Sound-to-Light Converter Schematic

Figure 1 shows a simple ambit for converting an audio arresting (such as one that comes from the apostle terminals of a CD player). The ambit basically consists of a buffer/amplifier date and three clarify circuits: a high-pass filter, a mid-pass filter, and a low-pass filter. The achievement of anniversary clarify ambit drives a light-emitting diode of altered color.

Simple Sound-to-Light Converter Schematic Circuit Diagram:


The ascribe arresting is fed to the absorber date through C1. The ethics of RF and RV1 should be called so that the absorber is able to drive the three filters absorbed to its output. The low-frequency, mid-frequency, and high-frequency apparatus of the ascribe arresting are alone accustomed to canyon through the low-pass clarify (bottom filter), the mid-pass clarify (middle filter), and the high-pass clarify (topmost filter), respectively, appropriately amid them from anniversary other.

Changes in the achievement of a clarify account its agnate achievement LED to about-face on and off. In effect, agriculture a connected audio arresting to the ascribe of this ambit causes the LED's to 'dance'.

Quartz Clock Timebase

Many electronic projects call for a timebase generator, accurate to a second or so. One way of producing this is with a microcontroller, quartz crystal and some software. But a far cheaper and simpler approach is to recycle an old analogue quartz clock. After investigating a number of clocks the author discovered that they all use the same drive method: a tiny solenoid coil is pulsed by a current that reverses direction once a second. In the module illustrated this coil is connected between pins Pulse1 and Pulse2. Most of the time both pins are ‘high’ at supply voltage but every second the clock electronics pull first one and then the other of the pins down to ground for about 25 ms.

Quartz Clock Timebase Circuit Diagram:

Quartz Clock-Timebase-Circuit Diagram

We need just five additional components to complete the circuit (see diagram). When either of the pulse pins is at ground potential, the corresponding PNP transistor conducts. Once a second a narrow pulse is produced, which is ideal for our own digital circuitry. The author himself uses one of these clock modules as timebase for a data logger with excel-lent results. Although the clock originally used a 1.5 V supply, this new arrangement works fine with a 3-V lithium batter y. After three months using the same battery there have been no problems whatsoever.

Quartz Clock Timebase Circuit Diagram[w]


Author : Claus Torstrick - Copyright :Elektor

Voice Activated Switch

This circuit uses an MC2830 to form a voice activated switch ( VOX ). A traditional VOX circuit is unable to distinguish between voice and noise in the incoming signal. In a noisy environment, the switch is often triggered by noise, or the activation sensitivity must be turned down.

Voice Activated Switch Circuit Diagram:

 Voice-Activated-Switch-Circuit diagram

This circuit overcomes this weakness. The switch is activated by voice level above the noise and not activated by background noise. This is done by utilizing the differences in voice and noise waveforms. Voice waveforms generally have a wide range of variation in amplitude, whereas noise waveforms are more stable. The sensitivity of the voice activation depends on the value of R6. The voice activation sensitivity is reduced from 3.0dB to 8.0dB above the noise if R6 changes from 14k to 7.0k .