USB Switch Schematic Circuit

Anyone experimenting or developing USB ported peripheral hardware soon be comes irritated by the need to disconnect and connect the plug  in order to reestablish communication with the PC. This process is necessary for example each time the peripheral equipment is reset or a new version of the firmware is installed. As well as tiresome it eventually leads to excessive contact wear in the USB connector. The answer is to build this electronic isolator which disconnects the peripheral device at the touch of a button. This is guaranteed to reduce any physical wear and tear and restore calm once again to the workplace.

Circuit image :

 USB Switch-Image

USB Switch Schematic Circuit Image

The circuit uses a quad analogue switch type 74HC4066. Two of the switches in the package are used to isolate the data path. The remaining two are used in a classic bistable flip-flop configuration which is normally built using transistors. A power MOSFET switches the power supply current to the USB device.  Capacitor C2 ensures that the flip flop always  powers-up in a defined state when plugged  into the USB socket (‘B’ in the diagram). The  peripheral device connected to USB socket ‘A’  will therefore always be ‘not connected’ until  pushbutton S2 is pressed. This flips the bistable, turning on both analogue gates in the data lines and switching the MOSFET on. The  PC now recognises the USB device. Pressing  S1 disconnects the device.

Circuit diagram :

USB Switch-Circuit-daigram

USB Switch Schematic Circuit Diagram

The circuit does not sequence the connections as a physical USB connector does; the power supply connection strips are slightly longer than the two inner data carrying strips to ensure the peripheral receives power before the data signals are connected. The electronic switch does not suffer from the same contact problems as the physical  connector so these measures are not required in the circuit. The  simple circuit can quite easily be constructed on a small  square of perforated strip-board. The design uses the 74HC(T)4066 type analogue switch, these have  better characteristics compared to the standard 4066 device. The USB switch is suitable for both low-speed (1.5 MBit/ s) and full-speed (12 MBit/s) USB ports applications but the proper ties of the analogue switches and perf-board construction  will not support hi-speed (480 MBit/s) USB operation.

The IRFD9024 MOSFET can pass a current of  up to 500 mA to the peripheral device with-out any problem.

 

Author : Rainer Reusch - Copyright : Elektor

Simple Low-Cost Digital Code Lock

Many digital code lock circuits have been published in this magazine. In those circuits a set of switches (conforming to code) are pressed one by one within the specified time to open the lock. In some other circuits, custom-built ICs are used and positive and negative logic pulses are keyed in sequence as per the code by two switches to open the lock.

Circuit diagram :

Simple Low-Cost Digital Code Lock-Circuit Diagram

Simple Low-Cost Digital Code Lock Circuit Diagram

A low-cost digital code lock circuit is presented in this article. Here the keying-in code is rather unique. Six switches are to be pressed to open the lock, but only two switches at a time. Thus a total of three sets of switches have to be pressed in a particular sequence. (Of these three sets, one set is repeated.) The salient features of this circuit are:

1. Use of 16 switches, which suggests that there is a microprocessor in-side.

2. Elimination of power amplifier transistor to energise the relay.

3. Low cost and small PCB size.

An essential property of this electronic code lock is that it works in monostable mode, i.e. once triggered, the output becomes high and remains so for a period of time, governed by the timing components, before returing to the quiescent low state. In this circuit, timer IC 555 with 8 pins is used. The IC is inexpensive and easily available. Its pin 2 is the triggering input pin which, when held below 1/3 of the sup-ply voltage, drives the output to high state. The threshold pin 6, when held higher than 2/3 of the supply voltage, drives the output to low state. By applying a low-going pulse to the reset pin 4, the output at pin 3 can be brought to the quiescent low level. Thus the reset pin 4 should be held high for normal operation of the IC.

Three sets of switches SA-SC, S1-S8 and S3-S4 are pressed, in that order, to open the lock. On pressing the switches SA and SC simultaneously, capacitor C3 charges through the potential divider comprising resistors R3 and R4, and on releasing these two switches, capacitor C3 starts discharging through resistor R4. Capacitor C3 and resistor R4 are so selected that it takes about five seconds to fully discharge C3.

Depressing switches S1 and S8 in unison, within five seconds of releasing the switches SA and SC, pulls pin 2 to ground and IC 555 is triggered. The capacitor C1 starts charging through resistor R1. As a result, the output (pin 3) goes high for five seconds (i.e. the charging time T of the capacitor C1 to the threshold voltage, which is calculated by the relation T=1.1 R1 x C1  seconds).

Within these five seconds, switches SA and SC are to be pressed momentarily once again, followed by the depression of last code-switch pair S3-S4.

These switches connect the relay to out-put pin 3 and the relay is energised. The contacts of the relay close and the solenoid pulls in the latch (forming part of a lock) and the lock opens. The remaining switches are connected between reset pin 4 and ground. If any one of these switches is pressed, the IC is re-set and the output goes to its quiescent low state. Possibilities of pressing these reset switches are more when a code breaker tries to open the lock.

LED D5 indicates the presence of power supply while resistor R5 is a cur-rent limiting resistor.

The given circuit can be recoded easily by rearranging connections to the switches as desired by the user.

 

Author : A. JEYABAL – Copyright : EFY

Circuit Guards Amplifier Outputs Against Overvoltage

A universal requirement for automotive electronics is that any device with direct connections to the wiring harness must be able to withstand shorts to the battery voltage. Though brutal, this requirement is necessary for reliability and for safety. One example of the need for this protection is an audio amplifier that produces indicator noises in the automotive interior. Though operating from a voltage of 3.3 or 5V, which is lower than the battery voltage, the amplifier must be able to stand off the full battery voltage.

Circuit diagram :

amplifier outputs against overvoltage

Figure 1 : This output circuit provides continuose protection against overvoltge faults

You can also use a protection network appropriate for these amplifiers for other automotive circuits (Figure 1). A dual N-channel MOSFET disconnects the amplifier’s outputs from the wiring harness in response to a high-voltage condition on either output. The MOSFETs, Q1A and Q1B, are normally on; zener diode D4 and its bias components drive the MOSFETs’ gates to approximately 11V. Dual diode D3 provides a diode-OR connection to the dc voltage on each output, thereby producing a voltage that controls the output of shunt regulator IC2. The circuitry protects IC1, a 1.4W Class AB amplifier suitable for audible warnings and indications for the automotive electronics.

During normal operation, the amplifier outputs’ dc components are at one-half of the VCC supply—2.5V in this case, for which VCC is 5V. The 11V gate drive fully enhances the MOSFETs, and the shunt-regulator output is off because its feedback input, Pin 5, is below its internal 0.6V threshold. If either output exceeds 5V, current flows through D3 into the R5/R6 divider, pulling the feedback terminal above its threshold. The shunt-regulator output then pulls the MOSFET-gate voltage from 11V almost to ground, which blocks high voltage from the amplifier by turning off the MOSFETs. The MOSFETs easily withstand the continuous output voltage, and the circuit returns to normal operation when you remove the short. Because the circuit does not respond instantaneously, zener diodes D1 and D2 provide protection at the beginning of a fault condition.

Figure 2. Figure 2. In Figure 1, one of U1's two audio outputs (top trace) is protected when its external terminal accidentally contacts an 18V supply voltage (2nd trace).

 

The waveforms of Figure 2 represent an operating circuit. One of the amplifier’s outputs (Trace 1) is a 1-kHz sine wave biased at a dc voltage of 2.5V. Trace 2 is the signal on the wire harness. It also starts as a 1-kHz sine wave biased at a 2.5V-dc voltage, but, at 200 µsec, it shorts to an 18V supply. Trace 3 is the shunt regulator’s output, initially biased at 11V but pulled to ground in response to the overvoltage condition. Trace 4 is current in the wire harness. Initially a sine wave, this current drops to zero in response to the overvoltage condition.

The components in Figure 1 optimize this circuit for 5V operation. For other voltages, you can adjust the R5/R6 resistor values. The shunt regulator must be able to function in saturation and, therefore, requires a separate supply pin in addition to the shunt output pin. The circuit repeatedly withstands 28V shorts without damage.

 

Source : www.maxim-ic.com

12V Fan Directly on 230 V

This circuit idea is certainly not new, but when it comes to making a trade-off between using a small, short-circuit proof transformer or a capacitive voltage divider (directly from 230 V mains voltage) as the power supply for a fan, it can come in very handy. If forced cooling is an afterthought and the available options are limited then perhaps there is no other  choice. At low currents a capacitive divider requires less space than a small,  short-circuit proof transformer.

Circuit diagram :

12V Fan Directly on 230 V-Circuit Diagram

12V Fan Directly on 230 V Circuit Diagram

R1 and R2 are added to limit the inrush current into power supply capacitor C2 when switching on. Because the maximum rated operating voltage of resistors on hand is often not known, we choose to have two resistors for the current limit. The same is true for the discharge resistors R3 and R4  for C1. If the circuit is connected to a mains  plug then it is not allowed that a dangerous voltage remains on the plug, hence R3 and R4.

Capacitor C1 determines the maximum current that can be supplied. Above that maximum the power supply acts as a current source. If the current is less then zener diode D1 limits the maximum voltage and dissipates the remainder of the power. It is best to choose the value of C1 based in the maximum expected current. As a rule of thumb, start with the mains voltage when calculating C1. The 12 V output voltage, the diode forward voltage drops in B1 and the voltage drop across R1 and R2 can be neglected for simplicity. The calculated value is then rounded to the nearest  E-12 value.

The impedance of the capacitor at 50 Hz is 1 / (2π50C). If, for example, we want to be able to supply 50 mA, then the required impedance is 4600 Ω (230 V/50 mA). The value for the capacitor is then 692 nF. This then becomes 680 nF when rounded. To compensate for mains voltage variations and the neglected voltage drops you could potentially choose the next higher E-12 value. You could also create the required capacitance with two smaller capacitors. This could also be necessary depending on the shape of the available space. It is best to choose for C1 a type of capacitor that has been designed for mains voltage applications (an X2 type, for example).

 

Author : Ton Giesberts - Copyright : Elektor

Multiband CW Transmitter

A radio frequency oscillator is at the heart of all radio transmitters and receivers. It generates high frequency oscillations, which are known as carrier waves. Here’s a continuous wave (CW) transmitter for transmitting.Morse code signals in the shortwave band (see Fig. 1). It is basically a variable frequency oscillator (VFO) whose frequency can be varied from 5.2 MHz to 15 MHz. The signal can be received in the shortwave band by any radio receiver. The circuit works off a 9V battery.

Circuit diagram :

Maliti Circuit diagram

Fig. 1 : Multiband CW Transmitter Circuit Diagram

Connect the Morse key (S1) across capacitor C5 as shown in the figure. Attach a telescopic antenna (capable of transmitting over a short distance) at the output terminal.The coil and gang capacitor C2 form the tank circuit. The coil (L) has a total of 60 turns. Winding details tails are given in Fig.2. Tappings on the coil allow selection of the required band. The frequency can be varied using C2 (main tuning).

Fig. 2 CircuitFig.2 : Multiband CW Transmitter

On reducing turns of the coil (using selector switch S2), the oscillator’s frequency increases because frequency is inversely proportional to inductance. Capacitor C1 couples the signal from the tank circuit to the base of transistor T1 (2N2222). Transistor T1 provides the required positive feedback for oscillation and transistor T2 (BC547) functions as the emitter follower. The output is taken from the emitter of T2.

For stable oscillations, use a polystyrene capacitor as C1. All other capacitors may be ceramic disk type. Enclose the circuit in a metal box for better shielding.

 

Source : EFY

Simple Cable Tester

This cable tester allows you to quickly check audio cables for broken wires. Because of the low power supply voltage, batteries can be used which makes the circuit portable, and therefore can be used on location.

Circuit diagram :

Simple Cable Tester-Circuit Diagram

Simple Cable Tester Circuit Diagram

The design is very simple and well organ-ised: using the rotary switch, you select which conductor in the cable to test. The corresponding LED will light up as indication of the selected conductor. This is also an indication that the power supply volt-age is present. If there is a break in the cable, or a loose connection, a second LED will light up, corresponding to the selected conductor. You can also see immediately if there is an internal short circuit when other than the corresponding LEDs light up as well.

You can also test adapter and splitter cables because of the presence of the different connectors.

Two standard AA- or AAA- batteries are sufficient for the power supply. It is recommended to use good, low-current type LEDs. It is also a good idea not to use the cheapest brand of connectors, otherwise there can be doubt as to the location of the fault. Is it the cable or the connector.

 

Author : Bert Vink - Copyright : Elektor

LM339-Low Voltage, High Current Time Delay

This circuit a LM339 quad voltage comparator is used to generate a time delay and control a high current output at low voltage. Approximatey 5 amps of current can be obtained using a couple fresh alkaline D batteries. Three of the comparators are wired in parallel to drive a medium power PNP transistor (2N2905 or similar) which in turn drives a high current NPN transistor (TIP35 or similar).

Circuit diagram :

Low Voltage, High Current Time Delay-Circuit Daigram

Low Voltage, High Current Time Delay Circuit Diagram

The 4th comparator is used to generate a time delay after the normally closed switch is opened. Two resistors (36K and 62K) are used as a voltage divider which applies about two-thirds of the battery voltage to the (+) comparator input, or about 2 volts. The delay time after the switch is opened will be around one time constant using a 50uF capacitor and 100K variable resistor, or about (50u * 100K) = 5 seconds. The time can be reduced by adjusting the resistor to a lower value or using a smaller capacitor. Longer times can be obtained with a larger resistor or capacitor. To operate the circuit on higher voltages, the 10 ohm resistor should be increased proportionally, (4.5 volts = 15 ohms).

Phantom Supply From Batteries

Professional (directional) microphones often require a phantom supply of 48 V. This is fed via the signal lines to the microphone and has to be of a high quality. A portable supply can be made with 32 AA-cells in series, but that isn’t very user friendly. This circuit requires just four AA-cells (or five rechargeable1.2 V cells). We decided to use a standard push-pull converter, which is easy to drive and which has a predictable output voltage. Another advantage is that no complex feedback mechanism is required. For the design of the circuit we start with the assumption that we have a fresh set of batteries.

Phantom Supply From Batteries-Image

We then induce a voltage in the secondary winding that is a bit higher than we need, so that we’ll still have a high enough voltage to drive the linear voltage regulator when the battery voltage starts to drop (refer to the circuit in Figure 1). T1 are T2 are turned on and off by an astable multivibrator. We’ve used a 4047 low-power multivibrator for this, which has been configured to run in an astable free-running mode. The complementary Q outputs have a guaranteed duty-cycle of 50%, thereby preventing a DC current from flowing through the transformer. The core could otherwise become saturated, which results in a short-circuit between 6V and ground.

 

Circuit diagram :

Phantom Supply From Batteries-Circuit Diagram Phantom Supply From Batteries Circuit Diagram

 

This could be fatal for the FETs. The oscillator is set by R1/C1 to run at a frequency of about 80 kHz. R2/R3 and D1/D2 make T1 and T2 conduct a little later and turn off a little faster, guaranteeing a dead-time and avoiding a short-circuit situation. We measured the on-resistance of the BS170 and found it was only 0.5 Ω, which isn’t bad for this type of FET. You can of course use other FETs, as long as they have a low on-resistance. For the transformer we used a somewhat larger toroidal core with a high AL factor. This not only reduces the leakage inductance, but it also keeps the number of windings small. Our final choice was a TX25/15/10-3E5 made by Ferroxcube, which has dimensions of about 25x10 mm.

This makes the construction of the transformer a lot easier. The secondary winding is wound first: 77 turns of a 0.5 mm dia. enamelled copper wire (ECW). If you wind this carefully you’ll find that it fits on one layer and that 3 meters is more than enough. The best way to keep the two primary windings identical is to wind them at the same time. You should take two 30 cm lengths of 0.8 mm dia. ECW and wind these seven times round the core, on the opposite side to the secondary connections. The centre tap is made by connecting the inner two wires together. In this way we get two primary windings of seven turns each.

The output voltage of TR1 is rectified by a full-wave rectifier, which is made with fast diodes due to the high frequency involved. C4 suppresses the worst of the RF noise and this is followed by an extra filter (L1/C5/C6) that reduces the remaining ripple. The output provides a clean voltage to regulator IC2. It is best to use an LM317HV for the regulator, since it has been designed to cope with a higher voltage between the input and output. The LM317 that we used in our prototype worked all right, but it wouldn’t have been happy with a short at the output since the voltage drop would then be greater than the permitted 40 V.

If you ensure that a short cannot occur, through the use of the usual 6k81 resistors in the signal lines, then the current drawn per microphone will never exceed 14 mA and you can still use an ordinary LM317. D7 and D8 protect the LM317 from a short at the input. There is virtually no ripple to speak of. Any remaining noise lies above 160 kHz, and this won’t be a problem in most applications. The circuit can provide enough current to power three microphones at the same time (although that may depend on the types used). When the input voltage dropped to 5.1 V the current consumption was about 270 mA. The reference voltage sometimes deviates a little from its correct value. In that case you should adjust R4 to make the output voltage equal to 48 V. The equation for this is: R4 = (48–Vref ) / (Vref / R5+50µA). To minimise interference (remember that we’re dealing with a switched-mode supply) this circuit should be housed in an earthed metal enclosure.

 

Author :Ton Giesberts - Copyright : Elektor

Nine Second LED Timer and Relay

This circuit provides a visual 9 second delay using 10 LEDs before closing a 12 volt relay. When the reset switch is closed, the 4017 decade counter will be reset to the 0 count which illuminates the LED driven from pin 3. The 555 timer output at pin 3 will be high and the voltage at pins 6 and 2 of the timer will be a little less than the lower trigger point, or about 3 volts.

Circuit diagram :

Nine Second LED Timer and Relay-Circuit Diagram

 Nine Second LED Timer and Relay Circuit Diagram

When the switch is opened, the transistor in parallel with the timing capacitor (22uF) is shut off allowing the capacitor to begin charging and the 555 timer circuit to produce an approximate 1 second clock signal to the decade counter. The counter advances on each positive going change at pin 14 and is enabled with pin 13 terminated low. When the 9th count is reached, pin 11 and 13 will be high, stopping the counter and energizing the relay. Longer delay times can be obtained with a larger capacitor or larger resistor at pins 2 and 6 of the 555 timer.

Cheapest Ever Motion Sensor

The RS-455-3671 sensor used in the Automatic Rear Bicycle Light project published in  the July/August 2010 edition can be replaced by a motion sensor that costs nothing instead of a fiver or thereabouts.

Cheapest Ever Motion Sensor-image 

The replacement is a homemade device, built from components easily found in the workshop of any electronics enthusiast. Effectively it works as a variable resistor, depending on the acceleration force to which the device is  submitted. A prototype presented a resistance of 200 kΩ when not moving, and 190 kΩ when dropping about 1 cm.

Cheapest Ever Motion Sensor-Circuit diagram

Constructing is easy. Cut off a piece of about 10 mm of copper tubing. Take a piece of conductive foam, the kind used to protect integrated circuits. Cut a rectangular piece of 10  x 50 mm. Roll up firmly until it can be push-fitted securely into the copper cylinder. Then insert a conductive wire through the centre of the cylinder, bend it and (optionally) add protective plastic sleeving to each side. This is the first contact. Finally, solder a thin wire to the copper cylinder. This is the second contact. The foam resistance is pressure dependent. Consequently, when the device moves due to an external force, the inertia of the cylinder causes varying pressure in the foam, resulting in a small change of resistance between the inner conductor and  the cylinder. Because of that, it’s important to ensure the cylinder vibration is not restricted in any way by the connecting wire or the PCB.

The comparator circuit shown here is capable of resolving the resistance change of the proposed foam/wire/copper sensor, allowing it to detect the motion of a vehicle for alarm or other purposes.

 

Author : Antoni Gendrau – Copyright : Elektor

6-Channel Running Light

The circuit of the running light comprises two integrated circuits (ICs), a resistor, a capacitor and seven light-emitting diodes (LEDs), Decade scaler IC2 ensures that the LEDs light sequentially. The rate at which this happens is determined by the clock at pin 14.

Circuit diagram :

6-Channel Running Light-Circuit Diagram

6-Channel Running Light Circuit Diagram

The clock is generated by IC1, which is arranged as an astable multivibrator. Its frequency is determined by R1-C1.

The touch switch, consisting of two small metal disks is optional. When switch S1 is in position ‘off ’, the circuit may be actuated by the touch switch. By the way, this enables the circuit to be used as an electronic die (in which case the LEDs have to be numbered from 1 to 6).

The running light is powered by a 9 V battery or mains adaptor. It draws a current not exceeding 20 mA.

Infrared Emitter & Detector

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.

Circuit diagram :

infrared-emitterdetector-cicuit.diagram

Infrared Emitter & Detector Circuit Diagram

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.

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.

Source / detector alignment method The transmitter can be mounted above the track with the phototransistor placed between the rails in places like hidden deposits. Place the transmitter and the detector at an angle would again be useful.

6 Band Graphic Equaliser Circuit with IC 741 Op-Amp

This circuit is 6 Band Graphic Equaliser ,you can adjust sound in low ,mid and high which circuit used IC 741 Op-Amp.

Circuit diagram :

6-band-graphic-equaliser-circuit-using-741-op-control

6 Band Graphic Equaliser Circuit with IC 741 Op-Amp

Audible Frequency spectrum is treated in six bands: 50Hz, 160Hz, 500Hz, 1.6kHz, 5kHz, 16kHz. All potentiometers are linear type of 100k. The circuit offers a lot of cut / boost for normal use.

Parts List :

R1, R2, R3, R4, R5, R6 27kΩ
R7 470kΩ
R8 330kΩ
R9 100kΩ
R10 4.7kΩ
R11 4.7kΩ
VR1, VR2, VR3, VR4, VR5, VR6 100kΩ
C1 100n (104)
C2 33n (333)
C3 10n (103)
C4 3.3n (332)
C5 1n (102)
C6 300pF (301)
C7 100µF 16V
C8 4.7µF 16V
C9 47µF 16V
IC1 741 Op amp

Power for the circuit of the amp / preamp itself derived. The wide range of power supply (6V-15V) makes the circuit very versatile. The power consumption is negligible.

Always on for PCs Circuit

Many enthusiasts will be using their PCs as data loggers, controllers or as web servers. ln these cases it is important that  the machine is kept powered up for as great a fraction of the time as possible, even if there has been a power cut or if the power button is inadvertently pressed by another member of the household. Today's operating systems offer a range  of automation options and it is perfectly possible to arrange things so that the computer starts itself up automatically.

Circuit diagram :

Always on for PCs-Circuit Diagram

Always on for PCs Circuit Diagram

The 'always on'circuit shown here automatically restarts an ATX PC in the above situations. There are just two components: a Schottky diode connecting the power but-ton pin on the motherboard to the +5 V line on the power supply, and a capacitor from the power  button pin to ground. The  capacitor  is a 68  pF tantalum type rated at 6.3 V, and the diode is a type SB 120, rated at 20 V and 1 A. The total component cost is in the sub-one-beer range!

The most convenient arrangement is to mount the circuit directly on a 4-way Molex disk drive power plug, insulating the capacitor and diode using heatshrink tubing. The assembly can then be plugged  into a spare socket on the power  supply.

The operation of the circuit is straightforward. When the +5 V supply fails (i.e., when the computer is turned off), the  power button pin on the motherboard is pulled low via the Schottky diode. This instructs the motherboard to power up again. As long as the +5  V supply is present, the diode blocks and the power button pin remains at high impedance, floating typically at around 3.3 V. The capacitor serves to filter out spikes and brief dropouts. ln its simpler version  the circuit replaces the power button on the case, and the computer can now only be switched on and off at the mains.

The author has tested the circuit on modern SuperMicro X8SAX and XSDTH-6F mother-boards as well as on an olderTyan  Tiger MPX. He found that the capacitor value should be reduced in some cases: the SuperMicro motherboards have a high internal pull-up  resistance which only charges the capacitor rather slowly.

Note that some PC keyboards have a 'Sleep' button which puts the computer into a low-power mode. ln this case the  circuit will not work, and you should either use a keyboard without such a button or disable sleep modes from within  the operating system.  ln its more advanced version the existing power button is retained in parallel with the circuit (see circuit diagram). The power button then  causes a 'graceful  shutdown' whereby the operating system can bring the computer to a halt in an orderly manner.

 

Author : Dr Rolf  Freitag - Copyright : Elektor

Cheap Bicycle Alarm Schematics Circuit

The author wanted a very cheap and simple alarm for some of his possessions, such as his electrically assisted bicycle. This alarm is based on a cheap window alarm, which has a time-switch added to it with a 1-minute time-out. The output  pulse of the 555 replaces the reed switch in the window alarm. The 555 is triggered by a sensor mounted near the front  wheel, in combination with a magnet that is mounted on the spokes. This sensor and the magnet were taken from a cheap bicycle computer.

Circuit diagram :

Cheap Bicycle Alarm-Circuit Diagram

Cheap Bicycle Alarm Circuit Diagram

The front wheel of the bicycle is kept unlocked, so that the reed  switch closes momentarily when the wheel turns. This  triggers the 555, which in turn activates the window alarm. The circuit around the 555 takes very little current and can  be powered by the batteries in the window alarm.  There  is just enough room  left inside the enclosure of the window  alarm to mount the time-switch inside it.

The result is a very cheap, compact device, with only a single cable going to the reed switch on the front wheel. And the noise this thing produces is just unbelievable! After about one minute the noise stops and the alarm goes back into standby mode. The bicycle alarm should be mounted in an inconspicuous place, such as underneath the saddle, inside a (large) front light, in the battery compartment, etc.

Hopefully the alarm scares any potential thief away, or at least it makes other members of the public aware that something isn't quite right.

Caution. The installation and use of this circuit may be subject to legal restrictions in your country, state or area.

 

Author : Gerard Seuren – Copyright : Elektor

NiCd Battery Charger

The design of the charger is similar to that of many commercially available chargers. The charger consists of a mains adaptor, two resistors and a light emitting diode (LED). In practical use, this kind of charger is perfectly all right.

Resistor R1 serves two functions: it establishes the correct charging current and it drops sufficient voltage to light the diode. This means that the LED lights only when a charging cur-rent flows into the battery. The charging current is about 1/4 of the battery capacity, which allows a slight overcharging, and yet the charging cycle is not too long (4–5 hours).

Circuit diagram :

NiCd Battery Charger-Circuit Diagram

NiCd Battery Charger Circuit Diagram

The value of the resistors may be calculated as follows, for which the nominal e.m.f. and the capacity of the battery must be known. Adjust the output of the mains adaptor to 1.17 times the nominal battery voltage plus 3.3 V, which is the potential across R1. Note that the adaptor must be capable of supplying a current of not less than half the battery capacity.

light

The value of R1 in ohms is equal to 3.3 divided by 1/4 of the battery capacity. The value of the resistors for various battery voltages is given in the Table. The battery capacity is taken as 1 Ah. The rating of R1 should be 5 W. If the battery to be charged has a different capacity, the theoretical value of R1 in the table must be divided by the battery capacity. Its actual value is the nearest one in the E12 series. For instance,if a 6 V battery with a nominal capacity of 600 mAh is to be charged, the value of R1 must be 20/0.6 = 33 ½.

Simple Sound Effects Generator

A Simple Sound Effects Generator Circuit uses a UM3561 IC to produce four different sound effects.

Circuit diagram :

Simple Sound Effects Generator-Circuit Diagram

Simple Sound Effects Generator Circuit Diagram

Notes:

Nothing too complicated here. The IC produces all the sound effects, the output at Pin 3 being amplified by the transistor. A 64 ohm loudspeaker can be substituted in place of the 56 ohm resistor and 8 ohm loudspeaker. The 2 pole 4 way switch controls the sound effects. Position 1 (as drawn) being a Police siren, position 2 is a fire engine sound, 3 is an ambulance and position 4 is a machine gun effect. The IC is manufactured by UMC and was available from Maplin electronics code UJ45Y. At the time of writing this has now been discontinued, but they have have limited stocks available.

Simple Multi-Color LED

How many different conditions do you reckon may be signalled with just one LED? Two, maybe three? Using this simple circuit, a lot more!

Circuit diagram :

Simple Multi-Color LED-Circuit Diagram

Simple Multi-Color LED Circuit Diagram

Admittedly, a two-colour LED is used here. Such a device consists of two light-emitting chips, usually red and green, encapsulated in the same case. It has three pins: two for the anodes, and one for the common cathode. In this way, each diode can be activated separately. Various mixed colours may be obtained by varying the current through the two diodes. At least four discrete colours are then easily perceived: pure red, pure green, orange (IR ≈ 2IG) and yellow (IG ≈ 2IR).

In the present circuit, the LED elements are driven by CMOS three-state buffers type 4503, which, unlike most CMOS ICs from the 4000 series, are capable of supplying up to 10 mA of output current. The LED cur-rents are limited by resistors R1 through R6, whose values invite experiments with brightness and colours according to your own taste.

The circuit was originally developed to indicate the state of three inputs, a, b, and c (non-binary, i. e., only one of these is at 1 at any time), with the con-figuration (a=b=c=0) representing the fourth state. The latter is decoded by NAND gate IC1. An additional effect is produced by gates IC1a and IC1b, which are connected up into an oscillator circuit producing approximately two pulses per second. These pulses are used to control the common-enable input, DA (pin 1) of the 4503, so as to produce a flickering effect. The oscillator is controlled by means of inputs ‘d’ and ‘e’. Pulling both of these logic high disables the oscillator and the LED driver. With e=0 and d=1 the outputs of the 4503 are switched to three-state, and the circuit is in power-down standby mode.

Although designed for a 12-V supply voltage, the circuit will happily work at any supply volt-age between 5 V and 16 V. Non-used inputs of CMOS ICs must, of course, be tied to ground via 10-100 kW resistors.

Autoconnect Disconnect Battery Charger

A simple battery charger that disconnects the battery when charge voltage reaches its nominal voltage and reconnects when battery voltage falls below a predefined level, can be designed using this circuit diagram.

Circuit diagram :

autoconnect-disconect-battery-charger-circuit diagram

Autoconnect Disconnect Battery Charger Circuit diagram

A fraction of the battery voltage is taken from the voltage divider R1-R2-R3-R4 and compare with a reference voltage with the help of IC2b. As long as the battery voltage is 0 V. The input current of AO produces a small voltage drop on R5, so IC2c pass in "0". Therefore, the relay remains disengaged.

When connecting a battery, low residual voltage provide switch of IC2c, diodes D4 and D5 are reverse biased, a voltage reference applied to the noninverting input of IC2d and relay is activated. In these conditions, the battery charge until its voltage reaches the nominal level.

Calibration is performed with a voltmeter connected to the output of IC2a, then P2 is adjusted, to obtain an indication of 3.45 V. Further, P1 rotates in the direction of maximum resistance. Replace battery with a stabilized power supply and set output voltage at 6V (6V position S1) or 12V (S1 in position 12 V), which is the voltage when charge is interrupted and adjust P1 until the relay works.

source : electroniq.net

Simple Timer for Very Long Periods

Simple mechanical timers, which you can buy for a couple of pounds in every home improvement centre, are suitable for switching something on and off one or more times per day. They can be used to control a wide variety of devices, such as  lamps inside or outside the house,lighting for bird cages and aquariums, sump pumps, battery chargers, etc.

 Simple Timer for Very Long Periods-image

If you need to control something over a longer period than the standard 24 hours, you can use two timers with the second one plugged  into the first one (see photos). To determine what you can do with this arrangement, you  first need to determine how often the load  needs to be switched. For example, if the  first timer has 48 tabs the shortest ‘on’ time  is 30 minutes in 24 hours. This means that the  second timer will run for 30 minutes every 24 hours, so the maximum duration of a full cycle is 48 days. A device such as a charger for diving torches can be connected to the second timer.

Simple Timer for Very Long Periods-Circuit Diagram

To prevent the ‘on’ time of the second timer from exceeding 24 hours, it is essential to keep the ‘on’ time of the second timer shorter than that of the first timer. If a maximum cycle time of 48 days is too short, you can also connect a third timer. With three timers, the maximum cycle time is 2304 days (one ‘on’ time in approximately 6.5 years).

As you can see from the photos, the second timer may interfere with the tabs of the first timer if they are plugged together with one on top of the other. This can be avoided by turning the second timer by 180 degrees relative to the first one.

Author : Dirk Visser  - Copyright : Elektor

Little Door Guard

If some intruder tries to open the door of your house, this circuit sounds an alarm to alert you against the attempted intrusion. The circuit (Fig. 1) uses readily available, low-cost components. For compactness, an alkaline 12V battery is used for powering the unit. Input DC supply is further regulated to a steady DC voltage of 5V by 3-pin regulator IC 7805 (IC2).

Circuit of the door guard

Fig. 1: Circuit of the door guard

Assemble the unit on a general-purpose PCB as shown in Fig. 4 and mount the same on the door as shown in Fig. 3. Now mount a piece of mirror on the door frame such that it is exactly aligned with the unit. Pin configurations of IC UM3561 and transistors 2N5777 and BC547 are shown in Fig. 2.

UM3561 and transistors

Fig. 2: Pin configurations of UM3561 and transistors 2N5777 and BC547

Initially, when the door is closed, the infrared (IR) beam transmitted by IR LED1 is reflected (by the mirror) back to phototransistor 2N5777 (T1). The IR beam falling on phototransistor T1 reverse biases npn transistor T2 and IC1 does not get positive supply at its pin 5. As a result, no tone is produced at its output pin 3 and the loudspeaker remains silent. Resistor R1 limits the operating current for the IR LED.

When the door isopened, the absence of IR rays at phototransistor T1 forward biases npn transistor T2, which provides supply to  positiveIC1. Now 3-sirensound generator IC UM3561 (IC1) gets power via resistor R5. The output of IC1 at pin 3 is amplified by Darlington-pair transistors T3 and T4 to produce the alert tone via the loudspeaker.

Back view of the door assembly

Fig. 3: Back view of the door assembly

Rotary switch S2 is used to select the three preprogrammed tones of IC1. IC1 produces fire engine, police and ambulance siren sounds when its pin 6 is connected to point F, P or A, respectively.

Suggested enclosure

Fig. 4: Suggested enclosure with major components layout

 

Author : T.K. Hareendran - Copyright : EFY

Car-Stereo LED Power (VU) Meter

This circuit senses AC audio voltage supplied to the car-radio loudspeakers and displays it as power using a LED bar graph, achieving at the same time an attractive visual effect. It is designed to cover common car-radio output power ranges, but can easily be modified to suit different needs. It is supplied from the 12 V car electrical system and is suitable for classical CC (Capacitor-coupled) as well as BTL (Bridge Tied Load) types of amplifier with no changes to the circuitry or connections at all. In fact, only the meaning of the LEDs changes — with BTL, the LED increments equal four times the CC value on the same load. CC-type amplifiers have the loudspeaker connected via a DC-decoupling capacitor at the output and ground (negative). BTL-type amplifiers, on the other hand, have the loudspeaker DC-coupled and ‘stretched’ between two equal, parallel, but phase-reversed outputs.

Project image :

Stereo LED-Power (VU) Meter-Image

Stereo LED Power (VU) Meter Image

The result compared to ‘CC’ is twice the voltage swing, hence quadrupling the power being fed to the same loudspeaker load. It is necessary to know to which of the two types this circuit is connected to only in order to correctly assign power levels (W) to the LEDs. CC-type have no DC voltage to ground at the outputs and return wires. The return wires are actually connected to the common ground (negative). BTL-type have approximately Vcc/2 at outputs and on the return wires too, explaining at the same time why no DC-decoupling capacitors are needed.

Circuit diagram :

Stereo LED Power (VU) Meter-Circuit Diagram

Stereo LED Power (VU) Meter Circuit Diagram

The LM3915N integrated circuit used in this circuit has been the subject of numerous publications in this magazine so will not will not be discussed again. In this application, the two LM3915Ns are configured as a LED bar graph drivers (pin 9 connected to pin 3), The ICs share the same power supply section. The audio input signal is fed via network C1/C2, R1, R2 (C3/C4, R5, R6) to pin 5 of IC1 (IC2). Only positive half-waves are processed by the ICs. Internally, the buffered input voltage is compared using comparators to the voltages along a resistor ladder network.

Pcb

The nominal +1.25 V reference source voltage (between pins 7 and 8) is applied across R3 (R7) to program the LED current. The programming current flows through R4 (R8) to achieve the desired reference voltage between pin 7 and ground. Here, only 2.0 V is developed, allowing this circuit to be used with low power amplifiers too. This voltage is applied to the ‘top’ of the on-chip resistor array (pin 6) and so determines the threshold at which the LED connected to the L10 output comes on. The other (low) side of the array (pin 4) is connected to ground. So, for an input voltage equal to or greater than the voltage at pin 6, all LEDs are on.

Pcb layout

At input voltages below the threshold set up for the lowest LED (89.3 mV or –27dB below the top LED) all LEDs are off. In order to limit power dissipation of IC1 and IC2, the LED voltage is stepped down to +5 V using IC3, C6 and C7. Diode D1 protects the circuit against reversed polarity. If a ‘dot’ mode graph is preferred pins 9 of IC1 and IC2 should be left open circuit. Using the listed value for R1 (R5), the indicator range covers audio power levels of 10 W into 4 Ω (CC) or 40 W into 4 Ω (BTL). Each ‘lower‘ LED indicates half the power of the previous ‘higher’ LED Only R1 (R5) needs to be redimensioned for different power levels. The value can be calculated from R1 = [R2 √(PO ZL) / (k * VRefOut)] – R2 where PO = maximum output power to be indicated (LED D2 or D12) ZL = loudspeaker impedance R2= R6 VRefOut = 2.0 V k = constant; 2 for BTL, 1 for CC The condition √ (PO ZL ) / (kVRefOut) ≥ 1 must be met. A small printed circuit board has been designed to allow a stereo version of the power indicator to be built.


The board is cut in two to separate the channels. The boards may be assembled in a sandwich construction with three inter-board connections A-A’, B-B’ and C-C’ made in stiff wire. IC3 should be secured to a small heatsink (10 K/W). Rectangular-face LEDs are recommended for this circuit. If on the other and 3mm dia. LEDs are used, these may have to be filed down a bit to be able to fit them in a straight row. The connection to the car radio should not present any problems. The audio signal is taken from the (+) loudspeaker connector for each channel and ground. The power supply leads to the indicator circuit are connected in parallel with car radio power supply. At a supply voltage of 14.4 V, the maximum and quiescent current consumption of the circuit was measured at 171 and 22 mA respectively.

Parts List :

Resistors:

  • R1,R5 = 22kΩ
  • R2,R6 = 10kΩ
  • R3,R7 = 820Ω
  • R4,R8 = 470Ω
Capacitors:
  • C1-C4 = 470nF, lead pitch 5mm
  • C5,C6,C7 = 10µF 63V radial
Semiconductors:
  • D1 = 1N4001
  • D2-D21 = LED, 3mm dia. or rectangular-face
  • IC1,IC2 = LM3915N-1 (National Semiconductor)
  • IC3 = 7805
Miscellaneous:
  • Heatsink for IC3 (10 K/W)

 

Author : R. Lali´c - Copyright : Elektor

Desktop Power Supply

Useful for electronics hobbyists, this linear workbench power supply converts a high input voltage (12V) from the SMPS of a PC into low output voltage (1.25 to 9 volts). An adjustable three-pin voltage regulator chip LM317T (IC1) is used here to provide the required voltages. The LM317T regulator, in TO-220 pack, can handle current of up to 1 amp in practice.

Fig. 1 shows the circuit of the desktop power supply. Regulator IC LM317T is arranged in its standard application. Diode D1 guards against polarity reversal and capacitor C1 is an additional buffer. The green LED (LED1) indicates the status of the power input. Diode D2 prevents the output voltage from rising above the input voltage when a capacitive or inductive load is connected at the output. Similarly, capacitor C3 suppresses any residual ripple.

Circuit diagram :

Desktop Circuit Daigram

Fig.1: Desktop Power Supply Circuit Diagram

Connect a standard digital voltmeter in parallel with the output leads to accurately set the desired voltage with the help of variable resistor VR1. You can also use your digital multimeter if the digital voltmeter is not available. Switch on S1 and set the required voltage through preset VR1 and read it on the digital voltmeter. Now the power supply is ready for use. 

  lm317

Fig.2:Pin Configuration of  LM317

The circuit can be wired on a common PCB. Refer Fig. 2 for pin configuration of LM317 before soldering it on the PCB. After fabrication, enclose the circuit in a metallic cover as shown in Fig. 3. Then open the cabinet of your PC and connect the input line of the gadget to a free (hanging) four-pin drivepower connector of the SMPS carefully. 

supply

Fig.3: Sugested power  supply box

12v Battery Charger

Battery charger shown in this circuit diagram can be used to charge one or more batteries with a total nominal voltage of 12 V (ie ten 1.2V or six 2V NiCd batteries or lead acid ) Misuse connection is impossible, because the batteries connected with incorrect polarity, output short circuit terminal or network loss have no effect on the charger or batteries.

Circuit diagram :

12v-battery-charger Circuit diagram

Charger for 12v Battery Circuit Diagram


Power is taken from the network through a transformer secondary voltage of 18 V. The output voltage from transformer is rectified by diodes D1 - D4 and filtered by C1, resulting in a voltage of 22 V across its C1. Exhausted batteries are charged in advance with a current of about 6 mA through R2-R4-R6, D5 and D8. Once the batteries have reached a voltage around 0.3 + / - 0.5 V, base-emitter voltage of T1 is large enough to bring the transistor into conduction. Charge indicator, D6, lights and also opens T2. Through R5-R6 pass a charge current of 60 mA.


If the battery is connected with reverse polarity or shorts power transistor T2 remains blocked and the current can not exceed 6-12 mA.

Triangular Wave Oscillator

This design resulted from the need for a partial replacement of the well-known 8038 chip,  which is no longer in production and there fore hardly obtainable.

An existing design for driving an LVDT sensor (Linear Variable Differential Transformer),  where the 8038 was used as a variable sine  wave oscillator, had to be modernised. It may  have been possible to replace the 8038 with an  Exar 2206, except that this chip couldn’t be used  with the supply voltage used. For this reason we  looked for a replacement using standard components, which should always be available.

Circuit diagram :

Triangular Wave Oscillator-Circuit Diagram

Triangular Wave Oscillator Circuit Diagram

In this circuit two opamps from a TL074 (IC1.A  and B) are used to generate a triangular wave,  which can be set to a wide range of frequencies using P1. The following differential amplifier using T1 and T2 is configured in such a way  that the triangular waveform is converted into  a reasonably looking sinusoidal waveform. P2  is used to adjust the distortion to a minimum.

The third opamp (IC1.C) is configured as a  difference amplifier, which presents the sine  wave at its output. This signal is then buffered by the last opamp (IC1.D). Any offset at the  output can be nulled using P3.

 

Author : Jac Hettema - Copyright : Elektor

40 LED Bicycle Light

The 555 circuit below is a flashing bicycle light powered with four C,D or AA cells (6 volts). Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second using RC values shown (4.7K for R1, 150K for R2 and a 1uF capacitor). Time intervals for the two lamps are about 107 milliseconds (T1, upper LEDs) and 104 milliseconds (T2 lower LEDs). Two transistors are used to provide additional current beyond the 200 mA limit of the 555 timer.

Circuit diagram :

40 LED Bycia-Circuit diagram

40 LED Bicycle Light Circuit Diagram

A single LED is placed in series with the base of the PNP transistor so that the lower 20 LEDs turn off when the 555 output goes high during the T1 time interval. The high output level of the 555 timer is 1.7 volts less than the supply voltage. Adding the LED increases the forward voltage required for the PNP transistor to about 2.7 volts so that the 1.7 volt difference from supply to the output is insufficient to turn on the transistor. Each LED is supplied with about 20 mA of current for a total of 220 mA. The circuit should work with additional LEDs up to about 40 for each group, or 81 total. The circuit will also work with fewer LEDs so it could be assembled and tested with just 5 LEDs (two groups of two plus one) before adding the others.

Remote Control Blocker

This circuit was designed to block signals from infrared remote controls. This will prove very useful if your children have the tendency to switch channels all the time. It is also effective when your children aren’t permitted to watch TV as a punishment. Putting the TV on standby and put-ting the remote control out of action can be enough in this case.

Circuit diagram :

Remote Control Blocker-Circuit Diagram

Remote Control Blocker Circuit Diagram

The way in which we do this is very straightforward. Two IR LEDs continuously transmit infrared light with a frequency that can be set between 32 and 41 kHz. Most remote controls work at a frequency of 36 kHz or 38 kHz.

The disruption of the remote control occurs as follows. The ‘automatic gain’ of the IR receiver in TVs, CD players, home cinema systems, etc. reduces the gain of the receiver due to the strong signal from the IR LEDs. Any IR signals from a remote control are then too weak to be detected by the receiver. Hence the equipment no longer ‘sees’ the remote control!

The oscillator is built around a standard NE555. This drives a buffer stage, which provides the current to the two LEDs. Setting up this circuit is very easy. Point the IR LEDs towards the device that needs its remote control blocked. Then pick up the remote control and try it out. If it still functions you should adjust the frequency of the circuit until the remote control stops working.

This circuit is obviously only effective against remote controls that use IR light!

 

Author : Paul Goossens - Copyright : Elektor

16 Stage Bi-Directional LED Sequencer

The bi-directional sequencer uses a 4 bit binary up/down counter (CD4516) and two "1 of 8 line decoders" (74HC138 or 74HCT138) to generate the popular "Night Rider" display. A Schmitt Trigger oscillator provides the clock signal for the counter and the rate can be adjusted with the 500K pot. Two additional Schmitt Trigger inverters are used as a SET/RESET latch to control the counting direction (up or down). Be sure to use the 74HC14 and not the 74HCT14, the 74HCT14 may not work due to the low TTL input trigger level.

Circuit diagram :

16 Stage Bi-Directional LED Sequencer-Circuit Diagram

16 Stage Bi-Directional LED Sequencer Circuit Diagram

When the highest count is reached (1111) the low output at pin 7 sets the latch so that the UP/DOWN input to the counter goes low and causes the counter to begin decrementing. When the lowest count is reached (0000) the latch is reset (high) so that the counter will begin incrementing on the next rising clock edge. The three lowest counter bits (Q0, Q1, Q2) are connected to both decoders in parallel and the highest bit Q3 is used to select the appropriate decoder. The circuit can be used to drive 12 volt/25 watt lamps with the addition of two transistors per lamp as shown below in the section below titled "Interfacing 5 volt CMOS to 12 volt loads"

Fridge Thermostat

What to do when the thermostat in your fridge doesn’t work any more? Get it repaired at (too) much expense or just buy a new one? It is relatively simple to make an electronic variation of a thermo-stat yourself, while saving a considerable amount of money at the same time. How-ever, be careful when working with mains voltages. This voltage remains invisible and can sometimes be fatal!

This design allows for five temperatures to be selected with a rotary switch. By selecting suitable values for the resistors (R1 to R7), the temperatures at the various switch positions can be defined at construction time. With the resistance values shown here, the temperature can be adjusted to 16, 6, 4, 2 and –22 °C. 16° C is an ideal temperature for the storage of wine, while 6, 4, and 2 degrees are interesting for beer connoisseurs and the minus 22°degrees position transforms the fridge into a large freezer. Note for wine connoisseurs: to prevent mould on the labels, it is necessary to place a moisture absorber or bag of silica gel in the fridge.

Circuit diagram :

Fridge Thermostat-Circuit Diagram

Fridge Thermostat Circuit Diagram

The circuit is built around an old work-horse among opamps, the 741. D1 pro-vides a stable reference voltage of 5 V across the entire resistor divider. P1 allows adjustment of the voltage at the node of R1 and R2. To use the above-mentioned temperatures as setpoints this voltage needs to be adjusted to 2.89 V. D2 is a precision temperature sensor, which can be used from –40 to +100 °C. The voltage across this diode varies by 10 mV per Kelvin. In this way D2 keeps an eye on the temperature in the fridge. The reference voltage derived from the voltage divider (selected with S1) is com-pared by IC1 with the voltage across the temperature sensor. Based on this, the 741 switches, via the zero voltage crossing driver (IC2), a triac that provides volt-age to the compressor motor. The zero voltage crossing IC switches only at the zero crossings of the mains voltage, so that interference from the compressor motor is avoided when turning on.

The power supply for the circuit is pro-vided by a simple bridge rectifier and filtered with two electrolytic capacitors of 220 µF each.

The design can also be used for countless other uses. You can, for example, make a thermostat for heating by swapping the inputs of the opamp.

Keep in mind the safety requirements when building and mounting the circuit.

Author : Tony Beekman - Copyright : Elektor

Unique Water Pump Controller

Here is a simple solution for automatic pumping of water to the overhead tank. Unlike other water-level indicators,  it  does not use probes to detect the water level and hence there is no probe corrosion problem. It has no direct contact with water, so the chance of accidental leakage of electricity to the water tank is also eliminated. Two important advantages of the circuit are that the water level never goes below a particular level and no modification in the water tank is required.

Circuit diagram :

Unique Water Pump Controller-circuit diagram

Fig.1 Unique Water Pump Controller Circuit diagram

Fig. 1 shows the circuit of the water-pump controller. The circuit uses an LDR-white LEDs assembly to sense the water level. It forms a triggering switch to energise the relay for controlling the pump. The LDR-LEDs assembly (shown in Fig. 2) is fixed on the inner side of the cap  of  the  water tank without making contact with water. The light reflected from  the water tank is used to control the resistance of LDR1.

Sensor circuit

Fig 2 Sensor circuit diagram

When the water level is high enough, light from the white LEDs (LED1 through LED3) reflects to fall on LDR1. This reduces the resistance of LDR1, increasing the voltage at the non-inverting input (pin 3)  of IC1. IC1  is used in the circuit as a  voltage comparator. Resistors R4 and R5 form a potential divider to fix half of supply voltage to the inverting input of IC1.

Normally, when the water tank is full, LDR1 gets more of reflected light because the distance between the water level and the face of LDR1 is minimal. When white light falls on LDR1, the voltage at the non-inverting input (pin 3) of IC1 increases and its output goes high. This high output makes pnp transistor T1 non-conducting and the relay remains de-energised. LED1 also remains ‘off.’ Since the water-pump power supply is connected to the normally-open (N/O)  contacts of  relay RL1, pumping is stopped.

When water level falls, the amount of  light reflected to LDR1 decreases and its resistance increases. This reduces the  voltage at pin 3 of IC1 and its output goes  low. This  low output from IC1 makes transistor T1 conduct. Relay RL1 energises to close the N/O  contacts and the motor  starts pumping water. LED1 glows to indicate the pumping of water.

Sensor assembly

Fig.3 Sensor assembly

Assemble the circuit on a general-purpose PCB and enclose in a suitable  cabinet. Solder the white LEDs-LDR1 assembly on a separate PCB and use a separate power supply for it. Mount LEDs behind the LDR. Otherwise, light from the LEDs will  affect the working of the circuit. Connect LDR1 to the main circuit board at ‘A’ and ‘B’ points.

Fix the LEDs-LDR1 assembly on the inner side of the water-tank cap as shown in Fig.  3. Orient the LEDs and the LDR such that when the water tank is full, the light emitted from the LEDs and reflected  from the water surface falls directly on  LDR1.  The  distance between the upper level of water and the LEDs-LDR setup should be minimal, ensuring that water doesn’t touch  LDR1. Otherwise, the circuit  will  not function properly. By using more white  LEDs, this  distance  can  be increased. Cover the LDR with a black tube to increase its sensitivity.

You can fix the main unit at a convenient place and connect it to the LEDs-LDR  assembly through wire. Select the relay according to the horse-power (HP) of the water pump. After  arranging the setup (with  maximum water in the tank), adjust VR1 until LED1 stops glowing. In this state, the relay should de-energise. When the water level decreases, the relay automatically energises to connect mains to the motor and it starts pumping water.

 

Author :D.Mohan Kumar - Copyright: EFY

A Simple Solar Cell Power System

A solar cell power system can be built using this electronic scheme. This electronic circuit is composed of three parts: a diode, solar cell panel and a rechargeable battery. Diode prevents battery discharge through the solar panel in the absence of sunlight or low light. Although diode is usually Schottky type, the direct voltage it can produce a considerable energy loss. Circuit uses a specials diode with low direct voltage.

Circuit Diagram :

solar-cells-charger.Circuit Diagram

A Simple Solar Cell Power System Circuit Diagram


To adjust the circuit, replace solar panel with adjustable stabilized voltage source, with current limiter set at a level which is not dangerous to the battery. Adjust power supply output at a level higher than 0.1 V than battery voltage. Then, adjust P1 until the point where IC1's output went into logical "1". Finally, with an ammeter if the battery is discharged when the source voltage is below the current battery voltage.

3D LED Pyramid

The author 'just wanted to do a bit of microcontroller programming'. However, the project rapidly grew into this impressive and visually attractive pyramid. The circuit consists essentially of a specially-sawn printed circuit board,  23 LEDs and a microcontroller. Despite the fact that the microcontroller  is a rather modest Atmel ATtiny2313, the author nevertheless has found room in the 2 KB flash memory for 16 different light sequences.

23 LDEs

The 23 LEDs are divided into three groups. The lower and middle sections consist of eight LEDs, while the upper section  has just seven. The microcontroller has only 20 pins, and so it is not feasible to provide a direct individual drive for each LED. The multiplexing approach adopted uses just eleven output port pins. Buffer transistors are used to increase the  current drive capability of each output.

23 LDEs Circuit Diagram

The software was written in assembler and can, as usual, be downloaded from the Elektor web pages accompanying this  article [1]  as either source code or as a hex file. The printed circuit board layout files are also available from the same  place, as well as a link allowing purchase of ready-made boards and pre-programmed microcontrollers.

Populating the printed circuit board is straightforward: there are some surface-mount components to be soldered,  but space is not tight. For best results,  it is best to choose LEDs with the widest possible viewing angle so that the pyramid  looks its best even when seen from the side. The author used type LO 1296 orange LEDs from Osram, which have a viewing angle of 160 '. A six- way connector is provided to allow in system programming  (l5P) of the microcontroller. The  configuration fuses are set to enable use of the internal4  MHz  clock source, which is divided down to 0.5 MHz by an  internal divider.  lf the fuses are not correctly programmed the light sequences will run too quickly, too slowly, or even not at all!

When everything is working, take an 11 cm length and  a 5.5 cm  length of 1.5 mmz solid copperwire and solder one end  of the shorter piece to the middle of the longer piece to make a 'T' shape. Pullthe  printed  circuit board spiral apart  so  that the T-shaped wire assembly fits underneath, and then solder it to the two pads as shown in the photograph. Fine-bore brass tubing can also be used instead of solid copperwire.

As well as the ISP connector a USB interface is provided, whose job is solely to provide a 5 V supply. An external 5 V mains adaptor would do the job equally well. Two jumpers affect the behaviour of the light pyramid: JP1 deter-mines  whether the sixteen sequences follow one another in strict order or at random;  and JP2 determines whether the light  patterns are displayed orwhether all LEDs will be continuously lit. S1 is a reset button, which will come in handy if you  wish to experiment with modifying the software.

Author : Lothar Goede - Copyright : Elektor