Home Network for ADSL

The increased availability of fast ADSL Internet connections has made it more attractive to install a small RJ45 Ethernet network in the home. Not only can you exchange files between computers, you will also have fast Internet access for everybody! This does of course require an ADSL modem with a router. It’s not possible to use a simple USB modem on its own. For laptops we recommend wireless Ethernet connections. If you find the laying of cables too difficult or inconvenient you can also add wireless capabilities to ‘ordinary’ PCs. You should bear in mind that the range of wireless connections could sometimes be disappointing. When a network is set up round a router you should use a star configuration for the cabling. This means that only a single PC is connected to each router socket.

The connecting cable may have a maximum length of 90 m and usually terminates at a connection box. You should use a CAT5 cable with 8 conductors for this, which is suitable for speeds up to 100 Mb/s. The 8 conductors are arranged in 4 pairs, with each pair twisted along the length of the cable. It is extremely important that the wires of each pair are kept together and that they are kept twisted as much as possible. At the connector ends you should therefore make sure that the non-twisted sections of the cable are kept as short as possible, at most a few centimetres. Should you fail to do this you may find that the network won’t operate at the full rated speed or possibly cause interference. The wiring itself is very simple. Connect the plugs to the cables such that each pin connects to the corresponding pin at the other end.

So pin 1 to 1, 2 tot 2 and so on. This also applies to all patch leads between the connection boxes and PCs (or if you prefer, the cable can go directly to the PC, without a connection box). It is only when two computers are connected directly together without a router that a crossover cable is required. The plugs are attached to the cable using a special crimping tool. It is also possible without the tool, using just a screwdriver, but this isn’t easy and we don’t recommend that you try it. The wires in the cable have different colours and there are no official standards in Europe how you use them (EN50173). However, the colour code in the American T568B standard is often used:
  • orange/white
  • orange
  • green/white
  • blue
  • blue/white
  • green
  • brown/white
  • brown
The coloured/white wires and the solid coloured wires alternate nicely. For Ethernet cabling you only need connections 1, 2, 3 and 6. The central contacts on pins 4 and 5 are in the middle of the green pair and may be used for analogue telephones. You then have to make sure that 4 and 5 aren’t connected to the Ethernet plugs because the voltages found on analogue telephone lines are high enough to damage an Ethernet card and/or router. Wires 4 and 5 should then be routed to an RJ11 telephone socket. We don’t recommend it, but it is possible. It is also possible to pass ISDN signals through the same RJ45 plugs and cabling. In this case you can’t use the same cable for both Ethernet and ISDN, since the latter uses pins 3/6 and 4/5.

If you use patch cables it helps to keep things organised by using coloured cables. Blue for Ethernet (red for a crossover cable), yellow for analogue telephones and green for ISDN. Sticky labels or coloured cable markers can also be used for identification when you can’t get hold of coloured cables. A new standard has recently been introduced, although you probably won’t use it in the home for a while. Since around two years ago you can also use a GG45 connector, which is compatible with RJ45. This has 4 extra contacts and is suitable for speeds up to 600 Mb/s (Category 7/Class F).

Author: Karel Walraven
Copyright: Elektor Electronics

Infrared Remote Extender

This project sprang from the need to be able to remotely control audio-visual equipment placed inside cupboards. RF-based commercial units such as those used for home theatre were found to be overkill for this application. The circuit is based on a commonly available infrared receiver module (IRX1) and a PIC12F675 microcontroller (IC1) – see circuit. Most infrared standards specify a nominal 38kHz carrier signal for data transmission, which the module receives and demodulates.

Circuit diagram:
Infrared Remote Extender Circuit Diagram
Digital data output:

The digital data output from the module is fed into GP2 (pin 5) of the PIC micro, where it’s received by the PIC program and duplicated on output GP1 (pin 6). This flashes the "Signal" LED to give a visual indication that the extender is receiving the remote control’s transmissions.

Copyright: Silicon Chip Magazine

Float Charger For NiMH Cells

Although not a new device, the LM317 is still a high-performance regulator. Its output voltage is essentially immune to fluctuations in load, supply voltage and temperature and this makes it ideal as the central element in a float charger for NiMH cells. Float charging has the advantage of keeping the cells fully charged and ready to use without the potential damage of long-term trickle charging or the cost of low-discharge cells. This works because NiMH cells do not have the memory problems associated with Nicads. The circuit is based on a conventional LM317 regulator. Resistors R2 & R3 and trimpot VR1 set the maximum output voltage to between 1.3V and 1.4V per cell. VR1 should be adjusted for a value of 1.35V per cell at the regulator output. Resistor R2 has been fixed at 240O. The formula for the voltage output is: Vout = 1.25*(1 + (R3 + VR1)/R2).

Circuit diagram:

Float Charger For NiMH Cells Circuit Diagram

Diode D1 protects the circuit against reverse polarity of the power supply and protects the LM317 should the power be disconnected while it is still connected to a charged battery pack. Resistor RCL and transistor Q1 limit the maximum current in the event of a short circuit or the connection of a severely discharged battery pack. LED2 provides an indication of voltage input to the charger. LED1 and the 680O resistor provide the same function for the charger output and also provide a minimum load for the regulator when the battery pack is nearing full charge. This is necessary to keep the regulator output from drifting up and damaging the batteries. The circuit uses an external DC plugpack and is suitable for four NiMH cells rated at 2.5Ah.

Table 1 gives alternative values for 1-10 batteries in series at peak charge currents of between 200mA to 600mA. If you are using the specified plug-pack and the TO-220 packaged LM317T, you will need a heatsink rated at 12°C/W or better for any design other than the 200mA single cell charger. A TO-3 packaged device with the correct plug-pack will be OK without a heat-sink for any of the 200mA configurations and up to four cells charging at 400mA.
Author: David Eather
Copyright: Silicon Chip Electronics

Simple Infrared Control Extender

Lots of consumer electronic equipment like TV sets, VCRs, CD and DVD players employs infrared remote control. In some cases, it is desirable to extend the range of the available control and this circuit fits the bill, receiving the IR signal from your remote control and re-transmitting it, for example, around a corner into another room. Photodiode D4 is connected to the inverting input of a 741 opamp through resistor R2 and capacitor C1. Since the BPW41 photodiode (from Vishay/Telefunken) needs to be reverse-biased to turn light energy into a corresponding voltage, it is also connected to the positive supply rail via R1. The non-inverting input of the ‘741 is held at half the supply voltage by means of equal resistors R3 and R4.

Circuit diagram:
Simple Infrared Control Extender Circuit Diagram

The opamp is followed by a BD240 after-burner transistor capable of supplying quite high current pulses through IR LEDs D2 and D3. However, the pulsed current through the LD274s should not exceed 100 mA or so, hence a fixed resistor is used in series with preset P1. D1 is an ordinary visible-light LED that flashes when an IR signal is received from the remote. With regard to the setting of P1, do not make the IRED current higher than necessary to reliably reach the final destination of the IR signal. Also, the currents mentioned above are peak levels due to the small duty factor of the IR pulses, the average current drawn from the battery will be much smaller. The directivity of the IR LEDs and consequently the range of the control extender may be increased by fitting the devices with reflective caps.
Author: Raj. K. Gorkhali - Copyright: Elektor Electronics July-August 2004

Cheap Pump Controller

This simple but effective circuit can be used to control water level in a container. The prototype is used to pump water out of a bucket that collects condensation from a home air-conditioning system. The design is based around a 555 timer (IC1). Although the timer in configured as a mono-stable, it lacks the usual timing capacitor from pin 6 to ground. Instead, a metal probe inserted in the water provides a current path to a second, grounded probe. When the water level in the container reaches a third ("high") probe, the trigger input (pin 3) is pulled low, switching the 555 output high and energizing the relay via transistor Q1.

Circuit diagram:
Cheap Pump Controller Circuit Diagram

Once the water level drops below the "low" probe, the threshold input (pin 6) swings high, switching the output (pin 3) low and the relay and pump off. The two 100kΩ pull-up resistors can be replaced with larger values if more sensitivity is required (eg, if the 555 doesn’t trigger). A switch (S1) can be included to bypass the relay for manual emptying. The "low" probe should be positioned so that the pump doesn’t run dry.

The high level probe is placed at the level that you want the pump to start. Since the water is held at ground potential, you must use stainless steel or copper wire to slow corrosion. With water fountain pumps available for less than $10, this circuit offers a cheap alternative for those who have an air-conditioner on an internal wall and don’t want to be continually emptying the bucket on humid days.
Author: Adrian Hudson - Copyright: Silicon Chip Electronics

Infrared Remote Receiver Has Four Outputs

This circuit enables any infrared (IR) remote control to control the outputs of a 4017 decade counter. It's quite simple really and uses a 3-terminal IR receiver (IRD1) to pick up infrared signals from the transmitter. IRD1's output is then coupled to NPN transistor Q1 via a 220nF capacitor. Transistor Q1 functions as a common-emitter amplifier with a gain of about 20, as set by the ratio of its 10kO collector resistor to its 470O emitter resistor. Q1 in turn triggers IC1, a 4047 monostable which in turn clocks a 4017 decade counter (IC2).

Circuit diagram:

Basically, IC1 provides a clock pulse to IC2 each time a remote control button is pressed. If you don't wish to use all 10 outputs from IC2, simply connect the first unused output to pin 15 (MR). In this case, only the first four outputs (O0-O3) of the counter are used and so the O4 output is connected to pin 15 to reset the counter on the fifth button press. Power for the circuit is derived from the mains via a transformer and bridge rectifier which produces about 15-27V DC. This is then fed to 3-terminal regulators REG1 & REG2 to derive +12V and +5V supply rails.
Author: Fred Edwards - Copyright: Silicon Chip Electronics

Contrast Control for LCDs

The adjustment control for the contrast of an LC-Display is typically a 10-k potentiometer. This works fine, provided that the power supply voltage is constant. If this is not the case (for example, with a battery power supply) then the potentiometer has to be repeatedly adjusted. Very awkward, in other words. The circuit described here offers a solution for this problem. The aforementioned potentiometer is intended to maintain a constant current from the contrast connection (usually pin 3 or Vo) to ground.

A popular green display with 2x16 characters ‘supplies’ about 200 µA. At a power supply voltage of 5 V there is also an additional current of 500 µA in the potentiometer itself. Not very energy efficient either. Now there is an IC, the LM334, which, with the aid of one resistor, can be made into a constant current source. The circuit presented here ensures that there is a current of 200 µA to ground, independent of the power supply voltage. By substituting a 2.2-k? potentiometer for R1, the current can be adjusted as desired.

Circuit diagram:The value of R1 can be calculated as follows: R1 = 227x10-6 x T / I. Where T is the temperature in Kelvin and I is the current in ampères. In our case this results in:
R1 = 227x10-6 x 293 /
R1 = 333R
Note that the current supplied by the LM334 depends on the temperature. This is also true for the current from the display, but it is not strictly necessary to have a linear relationship between these two. Temperature variations of up to 10° will not be a problem however. This circuit results in a power saving of over 25% with an LCD that itself draws a current of 1.2 mA. In a battery powered application this is definitely worth the effort! In addition, the contrast does not need to be adjusted as the battery voltage reduces. When used with LCDs with new technologies such as OLED and PLED it is advisable to carefully test the circuit first to determine if it can be used to adjust the brightness.

Circuit diagram:
Contrast Controller Circuit Diagram For LCDs

The value of R1 can be calculated as follows: R1 = 227x10-6 x T / I. Where T is the temperature in Kelvin and I is the current in ampères. In our case this results in:
  • R1 = 227x10-6 x 293 /
  • (200x10-6)
  • R1 = 333R
  • The current supplied by the LM334 depends on the temperature. This is also true for the current from the display, but it is not strictly necessary to have a linear relationship between these two. Temperature variations of up to 10° will not be a problem however. This circuit results in a power saving of over 25% with an LCD that itself draws a current of 1.2 mA. In a battery powered application this is definitely worth the effort! In addition, the contrast does not need to be adjusted as the battery voltage reduces. When used with LCDs with new technologies such as OLED and PLED it is advisable to carefully test the circuit first to determine if it can be used to adjust the brightness.
Author: Heino Peters
Copyright: Elektor Electronics

Voltage Controlled Power Supply Tester by OPA277

While testing the power supplies or discovering their potential problems, you must apply dynamic and static tests. This circuit, namely current sink, makes this job easier for you. It can draw 0 to 1.5A current from the load depending on the input voltage between 0 to 5V applied to the input. The two main components of the circuit are OPA277 and IRF530. OPA277 is a precision operational amplifier IC which features a max. VIO= 100 µV and IIB=4 nA. It makes a comparison between the voltage applied to its non-inverting terminal and the voltage across the resistor RSENSE.

The second is the STMicroelectronics' IR530 N-Channel Power MOSFET which is capable of delivering max. 14 A with VDS voltage of 100V and at a case temperature of 25 °C. It needs adequate heatsinking.  Since the MOSFET can dissipate a finite amount of maximum power, when you increase the power supply voltage, you must reduce the load current accordingly.

The voltage divider part including the R1 and R2 resistors allows to apply 0 to 0,495V to the non-inverting input when the input voltage is between 0 to 5V that results an output current range of 0 to 1.5A.

The output voltage can be found by the following relation;
where V+ is the voltage applied to the non-inverting terminal and calculated by;
V+ = [R2/(R1+R2)]VIN
So you can change the voltage divider resistors to draw more current from the load. In this instance, the supply voltage must be lowered not to exceed the maximum power dissipation of the MOSFET.

C3, C4, R3 and R4 components ensure the loop stability, yielding a circuit with a rise time of 1.4 µsec. So you can apply not only static tests by applying DC to the input, but also  dynamic test for instance by applying a pulsed input voltage to simulate fast load and transients.

The minimum supply voltage can be 0.735 V since the low channel resistance of the IRF530 is low. The negative output giving power supplies also can be tested by reversing the power supply terminal connections.

While connecting the power supply, especially during the dynamic tests, you must shorten the turn area as much as possible  because the pulsed load current produces radiated emissions and this may affect the circuit itself and the measuring equipment. Luca Bruno, ITIS Hensemberger Monza, Lissone, Italy - EDN, 20/3/2008

Speech Eroder

Nowadays, the speech quality on our telephone systems is generally very good, irrespective of distance. However, there are occasions, for instance, in an amateur stage production, or just for fun, when it is desired to reproduce the speech quality of yesteryear. The eroder circuit accepts an acoustic (via an electret micro-phone) or electrical signal. The signals are applied to the circuit inputs via C1 and C2, which block any direct voltage. The input cables should be screened. The signals are brought to (about) the same level by variable potential dividers P1-R1-R4 and P2-R2-R3, and then applied to the base of transistor T1. The level of the combined signals is raised by this preamplifier. The preamplifier is followed by an active low-pass filter consisting of T2–T4, C3, C4, R6–R8, and P4.

Circuit diagram:

Speech Eroder Circuit Diagram

Although, strictly speaking, P3 serves merely to adjust the volume of the signal, its setting does affect the filter characteristic. Note, by the way, that the filter is a rarely encountered current-driven one in which C3 and C4 are the frequency-determining elements. It has a certain similarity with a Wien bridge. Transistors T3 and T4, and resistors R8 and P4 form a variable current sink. The position of P4 determines the slope of the filter characteristic and the degree of overshoot at the cut-off frequency. The low-pass filter is followed by an integrated amplifier, IC1, whose amplification is matched to the input of the electronic circuits connected to the eroder with P5. The final passive, third-order high-pass filter is designed to remove frequencies above about 300 Hz. The resulting output is of a typical nasal character, just as in telephones of the past.
Author: T. Giesberts
Copyright: Elektor Electronics

Fridge Door Alarm Schematic 2nd Version

Alternative version of the popular circuit, 3V battery supply - Still operating at 1.3V

The main purpose of this design was to obviate a small defect of the very popular Fridge Door Alarm circuit, available on this website since 1999 and built by a lot of hobbyists. Unfortunately, that circuit stops operating when the battery voltage falls below about 2.6 - 2.7 Volts. This is due to the 4060 CMos IC used. In some cases, devices made by some manufacturers (but not Motorola's) fail to operate even at nominal 3V supply voltage.

A simple cure to this shortcoming could be the substitution of the original IC specified with a 74HC4060 chip: this should allow circuit operation down to 2V but, unfortunately, this IC is not easy to locate. For this reason, an equivalent circuit using about the same parts counting was developed, in order to allow safe operation even when battery voltage falls down to about 1.3V.

Circuit operation:

The circuit, enclosed in a small box, should be placed in the fridge near the lamp (if any) or close to the opening. With the door closed, the interior of the fridge is in dark, the photo resistor R2 presents a high resistance (>200K) thus clamping IC1 by holding C1 fully charged across R1 and D1. When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance (<2K) stopping C1 charging current.

Therefore IC1, wired as an astable multivibrator, starts oscillating at a very low frequency and after a period of about 24 sec. its output pin (#3) goes high, enabling IC2. This chip is also wired as an astable multivibrator, driving the Piezo sounder intermittently at about 5 times per second. The alarm is activated for about 17 sec. then stopped for the same time period and the cycle repeats until the fridge door closes.

Circuit diagram:
Fridge Door Alarm 2nd Version Circuit Diagram

R1 = 10K - 1/4W Resistor
R2 = Photo resistor (any type)
R3 = 2.2M - 1/4W Resistor
R4 = 1M - 1/4W Resistor
C1 = 10µF - 25V Electrolytic Capacitor
C2 = 100nF - 63V Polyester Capacitor
D1 = 1N4148 - 75V 150mA Diode
IC1 = 7555 or TS555CN CMos Timer IC
IC2 = 7555 or TS555CN CMos Timer IC
BZ1 = Piezo sounder (incorporating 3KHz oscillator)
B1 = 3V Battery (2 x 1.5V AA, AAA or smaller type Cells in series)

  • Delay time can be varied changing C1 and/or R3 values.
  • Beeper repetition rate can be varied changing C2 and/or R4 values.
  • Stand-by current drawing: 150µA.
  • Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.
  • Do not put this device in the freezer.

A Low Cost Hearing Aid

Small and portable unit, Useful for old men and old women

This low-cost, general-purpose electronic hearing aid works off 3V DC (2x1.5V battery). The circuit can be easily assembled on a veroboard. For easy assembling and maintenance, use an 8-pin DIP IC socket for TDA2822M.

Circuit Diagrams:

A Low Cost hearing Aid Schematic


P1 = 10K
R1 = 2.2K
R2 = 330K
R3 = 680R
R4 = 33R
R5 = 100R
R6 = 4.7R
R7 = 4.7R
R8 = 220R
C1 = 0.01uF-10V
C2 = 100nF-63V
C3 = 47uF-10V
C4 = 10uF-10V
C5 = 0.01uF-10V
C6 = 100uF-10V
C7 = 100nF-63V
C8 = 100nF-63V
D1 = Red LED
Q1 = BC547
IC1 = TDA2822M
EP1 = Mono Earphone 32R
SW1 = On-Off Switch

Circuit Operation:
In this circuit, transistor Q1 and associated components form the audio signal preamplifier for the acoustic signals picked up by the condenser microphone and converted into corresponding electrical signals. Resistor R5 and capacitor C3 decouple the power supply of the preamplifier stage. Resistor R1 biases the internal circuit of the low-voltage condenser microphone for proper working. The audio output from the preamplifier stage is fed to the input of the medium-power amplifier circuit via capacitor C2 and volume control P1.

The medium-power amplifier section is wired around popular audio amplifier IC TDA2822M (not TDA2822). This IC, specially designed for portable low-power applications, is readily available in 8-pin mini DIP package. Here the IC is wired in bridge configuration to drive the 32-ohm general-purpose monophonic earphone. Red LED (D1) indicates the power status. Resistor R8 limits the operating current of D1. The audio output of this circuit is 10 to 15mW and the quiescent current drain is below 1 mA.

Source : www.electronsforu.com

On-off Infrared Remote Control

Most homes today have at least a few infrared remote controls, whether they be for the television, the video recorder, the stereo, etc. Despite that fact, who among us has not cursed the light that remained lit after we just sat down in a comfortable chair to watch a good film? This project proposes to solve that problem thanks to its original approach. In fact, it is for a common on/off switch for infrared remote controls, but what differentiates it from the commercial products is the fact that it is capable of working with any remote control.

Therefore, the first one you find allows you to turn off the light and enjoy your movie in the best possible conditions. The infrared receiver part of our project is entrusted to an integrated receiver (Sony SBX 1620-52) which has the advantage of costing less than the components required to make the same function. After being inverted by T1, the pulses delivered by this receiver trigger IC2a, which is nothing other than a D flip-flop configured in monostable mode by feeding back its output Q on its reset input via R4 and C3. The pulse that is produced on the output Q of IC.2A makes IC.2B change state, which has the effect of turning on or turning off the LED contained in IC3.

Circuit diagram:
On-off Infrared Remote Control Circuit Diagram

This circuit is an opto triac with zero-crossing detection which allows our setup to accomplish switching without noise. It actually triggers the triac T2 in the anode where the load to be controlled is found. The selected model allows us to switch up to 3 amperes but nothing should stop you from using a more powerful triac if this model turns out to be insufficient for your use. In order to reduce its size and total cost, the circuit is powered directly from the mains using capacitor C5 which must be a class X or X2 model rated at 230 volts AC.

This type of capacitor, called ‘self-healing’, is the only type we should use today for power supplies that are connected to ground. ‘Traditional’ capacitors, rated at 400 volts, do not really have sufficient safety guarantees in this area. Considering the fact that the setup is connected directly to the mains, it must be mounted in a completely insulated housing. A power outlet model works very well and can easily be used to inter-space between the grounded wall outlet and that of the remote control device.

Based on this principle, this setup reacts to any infrared signal and, as we said before, this makes it compatible with any remote control. On the other hand, it has a small disadvantage which is that sometimes it might react to the ‘normal’ utilization of one of these, which could be undesirable. To avoid that, we advise you to mask the infrared receiver window as much as possible so that it is necessary to point the remote control in its direction in order to activate it.
Author: Christian Tavernier - Copyright: Elektor Electronics Magazine

Luxury Car Interior Light

This circuit is much more modest, but certainly still worth the effort. It provides a high quality interior light delay. This is a feature that is included as standard with most modern cars, although the version with an automatic dimmer is generally only found in the more expensive models. With this circuit it is possible to upgrade second hand and mid-range models with an interior light delay that slowly dims after the door has been closed. The dimming of the light is implemented by means of pulse-width modulation. This requires a triangle wave oscillator and a comparator.

Completed Project:

Two opamps are generally required to generate a good triangle wave, but because the waveform doesn’t have to be accurate, we can make do with a single opamp. This results in the circuit around IC1.A, a relaxation oscillator supplying a square wave output. The voltage at the inverting input has more of a triangular shape. This signal can be used as long as we do not put too much of a load on it. The high impedance input of IC1.B certainly won’t cause problems in this respect. This opamp is used as a comparator and compares the voltage of the triangular wave with that across the door switch. When the door is open, the switch closes and creates a short to the chassis of the car.

Parts Layout:

The output of the opamp will then be high, causing T1 to conduct and the interior light will turn on. When the door is closed the light will continue to burn at full strength until the voltage across C2 reaches the lower side of the triangle wave (about 5 V). The comparator will now switch its output at the same rate of the triangle wave (about 500 Hz), with a slowly reducing pulse width, which results in a slowly reducing brightness of the interior light. R8 and C3 protect the circuit from voltage spikes that may be induced by the fast switching of the light. The delay and dimming time can be adjusted with R6 and C2. Smaller values result in shorter times. You can vary the dimming time on its own by adjusting R1, as this changes the amplitude of the triangle wave across C1.

Circuit diagram:

Luxury Car Interior Light Circuit Diagram

R7 limits the discharge current of C2; if this were too big,it would considerably reduce the lifespan of the capacitor. There is no need to worry about reducing the life of the car battery. The circuit consumes just 350 µA when the lamp is off and a TLC272 is used for the dual opamp. A TL082 will take about 1 mA. These values won’t discharge a normal car battery very quickly; the self-discharge is probably many times higher. It is also possible to use an LM358, TL072 or TL062 for IC1. R8 then needs to have a value between 47 Ω and 100 Ω. Since T1 is always either fully on or fully off, hardly any heat is generated.

At a current of 2 A the voltage drop across the transistor is about 100 mV, giving rise to a dissipation of 200 mW. This is such a small amount that no heatsink is required. The whole circuit can therefore remain very compact and should be easily fitted in the car, behind the fabric of the roof for example.

R1,R2,R6 = 120kΩ
R3,R4 = 100kΩ
R5 = 470Ω
R7 = 100Ω
R8 = 220Ω
C1 = 10nF
C2 = 100µF-25V
C3 = 10µF-25V
T1 = BUZ10
IC1 = TLC272CP
Author: Cuno Walters
Copyright: Elektor Electronics

Model Railway Turnout Control

This small circuit can be used to control model railway turnouts operated by AC voltages. A logic level in the range of 5–12 V can be used as the control signal. The coils of the turnout are switched using triacs. Changes in the logic level of the input signal are passed on by the buffer stage built around T1 and T2. The buffer stage is included to boost the current available at the gates of the triacs. If the input goes high, this positive change is passed through via C1. That causes a positive current to flow through D2 (D2 is reverse biased) to the gate of T3. That triac switches on, and power is applied to the turnout coil.

Circuit diagram:
Model Railway Turnout Control Circuit Diagram

This situation persists until C1 is fully charged. No more current flows after that, so the triac does not receive any gate current and switches off. If the input is set low, a negative current flows briefly via C1. It can flow through D2, but not through D1. T4 is switched on now, and the other turnout coil is energised. This circuit takes advantage of the fact that triacs can be triggered by negative as well as positive gate currents. If the turnout coils are energised for too long, you should reduce the value of C1.

If they are not energised long enough, increase the value of C1. The TIC206D can handle several ampères, so it can easily drive just about any type of turnout coil. You can also use a different type of triac if you wish. However, bear in mind that the TIC206 requires only 5 mA of gate current, while most triacs want 50 mA. That will cause the switching times to become quite short, so it may be necessary to reduce the value of R1.
Author: Hans Zijp - Copyright: Elektor Electronics

Flickering Light II

Regardless of whether you want to effectively imitate a house fire, a campfire, or light from welding, the circuit described here fills the bill without using a microcontroller, although it does use a larger number of components (including some truly uncommon ones). The circuit is based on three oscillators, which are built using unijunction transistors (UJTs). Each oscillator has a different frequency. The output voltages are mixed, which produces the flickering effect. A unijunction transistor consists of an n-type bar of silicon between two ohmic (non-barrier) base contacts (B1 and B2). The effective resistance is controlled by the p-type emitter region. The designation ‘transistor’ is a somewhat unfortunate choice, since it cannot be used for linear amplification.

UJTs are suitable for use as pulse generators, monostable multivibrators, trigger elements and pulse-width modulators. If a positive voltage is applied to the emitter (E), the capacitor charges via the resistor. As soon as the voltage on the emitter reaches approximately half the supply voltage (for a 2N2645, the value lies in the range of 56–75 %), the UJT ‘fires’ and the capacitor discharges via base B1 and the resistor, generating a positive pulse. The UJT then returns to the non-conduct state, and the process just described repeats periodically. The frequency can be approximately given by the formula f ˜ 1/(RC) The frequency is independent of the value of the supply voltage (which must not exceed 35 V).

The maximum emitter blocking voltage is 30 V, and the maximum permissible emitter current is 50 mA. The values of resistors R1, R2 and R3 can lie between 3 k? and 500 k?. If necessary, the frequency can be varied over a range of 100:1 by using a trimpot instead of a fixed resistor. The frequencies from the three pulse generators are mixed by connecting them to the IR diode of a triac optocoupler via R4. The optocoupler, a type MOC3020, K3030P or MCP3020, can handle a maximum load current of 100 mA. The triac triggers at irregular intervals and generates the desired flickering light in the two small lamps, L1 and L2, which are connected in series to the transformer secondary.

Circuit diagram:

Flickering Light II Circuit Diagram

The light effect can be noticeably improved by using a MOC3040, which contains a zero-voltage switch, since its generates irregular pauses of various lengths when suitable frequencies occur in the individual oscillators. The zero-voltage switch does not switch while the current is flowing, but only when the applied ac voltage passes through zero. An integrated drive circuit (zero crossing unit) allows full half-waves or full cycles to pass (pulse-burst control) Due to the flickering effect arising from its switching behaviour, it is not suitable for normal lighting, but here this just what we want. This version of the optocoupler is also designed for a maximum current of 100 mA.

For a small roof fire or the light of a welding torch in a workshop, two small incandescent lamps connected in series and rated at 6 V / 0.6 A (bicycle taillight bulbs) or a single 12-V lamp (rated at 100 mA) is adequate. If it is desired to simulate a large fire, a triac (TIC206D, rated at 400 V / 4 A, with a trigger current of 5 mA) can be connected to the output of the circuit and used to control a more powerful incandescent lamp. As continuous flickering looses its attraction for an interested observer after a while (since no house burns for ever, and welders also take breaks), it’s a good idea to vary the on and off times of the circuit. This is handled by a bipolar Hall switch (TLE4935L), which has such a small package that it can fitted between the sleepers of all model railway gauges, including Miniclub (Z Gauge), or even placed alongside the track if a strong permanent magnet is used.

If a magnet is fixed somewhere on the base of a locomotive such that the south pole points toward the package of the Hall switch (the flattened front face with the type marking), the integrated npn transistor will switch on and pull the base of the external pnp transistor negative, causing the collector–emitter junction to conduct and provide the necessary ‘juice’ for the unijunction transistors. If another traction unit whose magnet has it s north pole pointing toward the Hall switch passes a while later, the switch will be cut off and the flickering light will go out. Of course, you can also do without this form of triggering and operate the device manually.
Author: Robert Edlinger
Copyright: Elektor Electronics

IrDA Interface

Many modern motherboards are equipped with an infrared data interface compliant with the IrDA standard, but this interface not very often used. However, it is not difficult to build a data transmission module and connect it to the corresponding header. As can readily be seen from the schematic diagram, this doesn’t exactly involve a large array of ICs. This is because transceiver ICs are available for the IrDA standard, so only a few passive components have to be added to obtain an operational circuit. The author has successfully built this circuit many times using the TFDU5102 from Vishay Semiconductors (formerly Telefunken). If this IrDA transceiver is no longer available (it has been officially discontinued), the largely pin- and function-compatible TFDU6102 can be used without any problems.

IrDA Interface Circuit Diagram

This IC is faster and meets the latest IrDA specification. The TFDU6102 low-power receiver IC supports IrDA at data rates up to 4 Mbit/s (FIR), HP-SIR, Sharp ASK, and carrier-based remote control modes up to 2 MHz. The IC contains a photodiode, an infrared emitter and CMOS control logic. The IC also has internal protection against electromagnetic immissions and emissions, so no external screening is necessary. The IC works with a supply voltage of 2.7–5.5 V, so it is suitable for use in desktop PCs, notebooks, palmtops, and PDAs. It is also used in digital still and video cameras, printers, fax machines, copiers, projectors, and many other types of equipment.

The author has designed a printed circuit board for the IrDA module that is only 20 × 20 mm square. Of course, this means that all of the components are SMD types. The TFDU6102 in the ‘babyface’ package is available in upright and flat versions. Here the upright version (suffix ‘TR3’) is used. Thanks to its small size, the assembled circuit board can easily be placed behind a drive bay cover or the like. It is connected to the motherboard by a five-way flat cable. The pin assignments for header X1 must match the mating connector on the motherboard. After you have fitted the module, you may have to edit the BIOS settings to activate the UART for IrDA operation. These settings enable the (Windows) operating system to boot the new device and automatically install it. You may have to briefly insert the Windows CD to modify the settings. There is an abundance of free programs on the Internet that use the IrDA interface.

R1 = 7Ω5 (shape 1210)
R2 = 47 Ω (shape 1206)
R3 = 100 k (shape 1206)
C1 = 100nF (shape 1206)
C2 = 4µF7 (shape 1210)
IC1 = TFDU6102TR3 (Vishay) (Farnell)
X1 = 5-way SIL pinheader
Author: A. Bitzer
Copyright: Elektor Electronics

500W Low Cost 12V to 220V Inverter

Attention: This Circuit is using high voltage that is lethal. Please take appropriate precautions

Using this circuit you can convert the 12V dc in to the 220V Ac. In this circuit 4047 is use to generate the square wave of 50hz and amplify the current and then amplify the voltage by using the step transformer.

How to calculate transformer rating
The basic formula is P=VI and between input output of the transformer we have Power input = Power output
For example if we want a 220W output at 220V then we need 1A at the output. Then at the input we must have at least 18.3V at 12V because: 12V*18.3 = 220v*1
So you have to wind the step up transformer 12v to 220v but input winding must be capable to bear 20A.

Wireless On-Off Switch

Small and simple circuit, Suitable for home appliances

Normally home appliances are controlled by means of switches, sensors, etc. However, physical contact with switches may be dangerous if there is any shorting. The circuit described here requires no physical contact for operating the appliance. You just need to move your hand between the infrared LED (D2) and the phototransistor (Q1). The infrared rays transmitted by D2 is detected by the phototransistor to activate the hidden lock, flush system, hand dryer or else. This circuit is very stable and sensitive compared to other AC appliance control circuits. It is simple, compact and cheap. Current consumption is low in milliamperes. The circuit is built around an IC CA3140, D2, phototransistor and other discrete components.
Circuit Diagram:

R1 = 470R
R2 = 100K
R3 = 3.3K
R4 = 10K
D1 = 1N4007
Q1 = L14F1
RL = 5Vdc Relay
IC = CA3140
Q2 = BC548

Circuit Operation:
When regulated 5V is connected to the circuit, D2 emits infrared rays, which are received by phototransistor Q1 if it is properly aligned. The collector of Q1 is connected to non-inverting pin 3 of IC1. Inverting pin 2 of IC1 is connected to voltage-divider preset R4. Using preset R4 you can vary the reference voltage at pin 2, which also affects sensitivity of the phototransistor. Op-amp IC1 amplifies the signal received from the phototransistor. Resistor R3 controls the base current of transistor BC548 (Q2). The high output of IC1 at pin 6 drives transistor Q2 to energies relay RL1 and switch on the appliance, say, hand dryer, through the relay contacts. The working of the circuit is simple. In order to switch on the appliance, you simply interrupt the infrared rays falling on the phototransistor through your hand. During the interruption, the appliance remains on through the relay. When you remove your hand from the infrared beam, the appliance turns off through the relay. Assemble the circuit on any general-purpose PCB. Identify the resistors through colour coding or using the multimeter. Check the polarity and pin configuration of the IC and mount it using base. After soldering the circuit, connect +5V supply to the circuit.

Source : www.electronicsforu.com

A Very Useful Timed Beeper Circuit Schematic

Beeps 7.5 seconds after a preset time, Adjustable time settings: 15s. 30s. 1min. & others

This circuit is intended for alerting purposes after a certain time is elapsed. It is suitable for table games requiring a fixed time to answer a question, or to move a piece etc. In this view it is a modern substitute for the old sandglass. Useful also for time control when children are brushing teeth (at least two minutes!), or in the kitchen, and so on.
Circuit diagram:
Timed Beeper Circuit Diagram
R1 = 220R
R2 = 10M
R3 = 1M
R4 = 10K
R5 = 47K
C1 = 100nF-63V
C2 = 22µF-25V
D1 = 1N4148
D2 = 3mm. Red LED
Q1 = BC337
P1 = SPST Pushbutton (Start)
P2 = SPST Pushbutton (Reset)

PS = Piezo sounder (incorporating 3KHz oscillator)
B1 = 3V Battery (2 AA 1.5V Cells in series)
IC1 = CD4081 Quad 2 input AND Gate IC
IC2 = CD4060 14 stage ripple counter and oscillator IC
SW1 = 4 ways Switch (See notes)

Circuit operation:
Pushing on P1 resets IC2 that start oscillating at a frequency fixed by R3 & C1. With values shown, this frequency is around 4Hz. LED D2, driven by IC1A & B, flashing at the same oscillator frequency, will signal proper circuit operation. SW1 selects the appropriate pin of IC2 to adjust timing duration:
  • Position 1 = 15 seconds
  • Position 2 = 30 seconds
  • Position 3 = 1 minute
  • Position 4 = 2 minutes
When the selected pin of IC2 goes high, IC1C drives Q1 and the piezo sounder beeps intermittently at the same frequency of the LED. After around 7.5 seconds pin 4 of IC2 goes high and IC1D stops the oscillator through D1. If you want to stop counting in advance, push on P2.

  1. SW1 can be any type of switch with the desired number of ways. If you want a single fixed timing duration, omit the switch and connect pins 9 & 13 of IC1 to the suitable pin of IC2.
  2. The circuit's reset is not immediate. Pushing P2 forces IC2 to oscillate very fast, but it takes some seconds to terminate the counting, especially if a high timer delay was chosen and the pushbutton is operated when the circuit was just starting. In order to speed the reset, try lowering the value of R5, but pay attention: too low a value can stop oscillation.
  3. Frequency operation varies with different brand names for IC2. E.g. Motorola's ICs run faster, therefore changing of C1 and/or R3 values may be necessary.
  4. You can also use pins 1, 2, 3 of IC2 to obtain timings of 8, 16 and 32 minutes respectively.
  5. An on-off switch is not provided because when off-state the circuit draws no significant current.

Fridge-Door Open Alarm Circuit Project

It beeps if the fridge door is left open for too long or hasn't closed properly, to stop food from spoiling. There are lots of other uses as well. A refrigerator or freezer door that is left open or ajar may cause the food contents to spoil. In some cases, the internal temperature of the fridge or freezer will be maintained if the refrigeration system can cope with the open door.

Complete project:

But without the door sealing in the cold air, it may be a losing battle. Running costs will certainly rise. Typically, refrigerators and freezers are in constant use in the summer months and so it is important to ensure that the door is not open for any longer than is necessary. Otherwise the fridge or freezer will not be able to keep the contents cool. And it will cost more money to needlessly run the fridge’s compressor in a futile effort to keep the contents cool.

Circuit looks like:

Even the most diligent fridge user may sometimes leave the door of the fridge or freezer open without realizing it. And tilting the fridge or freezer slightly backward so that the door will fall shut is not completely fool proof as there may be an obstruction inside the door. The obstruction could be because an item inside the compartment has moved or fallen over or because the compartment is too full. This is where the Fridge Alarm is useful.

It warns when the door of the refrigerator or freezer is left open for longer than a preset time period. It is great for indicating when someone is standing with the door open for too long and a real asset in warning when the door looks shut but is still partially ajar. The fridge alarm operates by detecting when any light enters the compartment area. Therefore it is just as useful for freezers (which normally do not have a light) as it is for fridges (which normally do). As long as there is some ambient light which the alarm can react to, it will operate.

Parts layout:

PCB layout:

Circuit diagram:

The alarm will sound if the light is present for longer than the preset period and will continue to sound until the door is closed. In practice, the preset period is adjusted so that in normal use the alarm will not sound. It will sound when the door is left wide open for too long or if left slightly ajar.

  • You don't have to house it in a transparent box, as we did . . . but if you don't, you'll need another hole in the appropriate place on the box wall so light can strike the LDR inside.

PCB layout has been added to download. Please click on the image below and get the PCB in EPS format. After downloading, you can view PCB in Corel Draw, Adobe Acrobat or Adobe Photoshop.
 Free Download TARGET 3001 V13 PCB-POOL Edition

Thermal Fan Controller By IC 741

The controller uses one or more ordinary silicon diodes as a sensor, and uses a cheap opamp as the amplifier. I designed this circuit to use 12V computer fans, as these are now very easy to get cheaply. These fans typically draw about 200mA when running, so a small power transistor will be fine as the switch. I used a BD140 (1A, 6.5W), but almost anything you have to hand will work just as well.

Circuit diagram:

Thermal Fan Controller Circuit Diagram
Source: ESP

Cat and Dog Repeller

Nowadays, just about every house has an outside lamp with a motion sensor. Such a device eliminates the need to feel your way to the front door, and it apparently also scares away intruders. The only problem is that free-running dogs and cats in the neighborhood have little regard for such lamps and continue to deposit their excrement in the garden, once they have found a habitual location there for this purpose. This gave rise to the idea of connecting a sort of siren in parallel with the outside lamp to clearly advise dogs and cats that they are not welcome.

Naturally, it would be nice to avoid startling the entire neighborhood with this alarm signal. Here we can take advantage of the fact that dogs and cats have a significantly better sense of hearing than people. Not only are their ears more sensitive, they can also perceive significantly higher frequencies. With people, the upper limit is around 18 kHz, but dogs and cats can hear frequencies in excess of 20 kHz. We can take advantage of this by building a siren that emits a frequency just above 20 kHz. This will scare off dogs and cats, but people will simply not hear it.

All we need for this is an oscillator with an amplifier stage and a tweeter that can reproduce such high frequencies, such as a piezoelectric tweeter. The schematic diagram shows how easily this can be implemented. The power supply for the entire circuit is formed by the components up to and including C2. The 230-V leads are connected in parallel with the motion-sensor lamp. C1 and R1 provide capacitive coupling to reduce the 230 V to an acceptable voltage. A DC voltage of approximately 9.1 V is generated from this voltage using a bridge rectifier and D1, filtered and buffered by C2. The oscillator is built around R3, C3 and IC1a.

Cat and Dog Repeller Circuit Diagram

The frequency of this oscillator is rather dependent on the specific characteristics of IC1, so the values shown here should be regarded as guidelines. If the oscillator frequency is too high, it can be reduced by increasing the value of R3 and/or C3. If the frequency is too low (which means that the siren tone it is audible), the value of R3 and/or C3 should be increased. The square-wave signal from the oscillator is applied to the input of an H bridge composed of several Schmitt triggers in combination with the final output stages (T1–T4). This approach causes the peak-to-peak value of the square wave signal to be twice the supply voltage.

As a result, a respectable 18 V is obtained across the piezoelectric tweeter, which is sufficient to produce a quite loud whistle tone. When building the circuit, you should bear in mind that it is directly powered from 230 V and not electrically isolated from the mains network. It is thus necessary to avoid contact with all of the components when the circuit is in use. In practice, this means that the circuit must be fitted into a well-insulated, waterproof box. If you want to test the circuit, it is a good idea to first discharge C1 using a resistor, since it can hold a dangerous charge. You must also ensure that components F1, C1, R1 and B1 all have a mutual insulation separation of at least 6 mm!
Author: I. Fietz
Copyright: Elektor Electronics

Room Recorder

My wife was working on a doctoral dissertation and needed to do some field work involving personal interviews in various settings. What would be the best way, technically speaking, to record the interviews? To pass a tape recorder or microphone back and forth seemed too awkward and clipping wired microphones to interviewees didn’t make for a particularly informal atmosphere. Radio microphones seemed overly expensive, too. After some thought, I can up with the "Room Recorder", an add-on microphone preamplifier circuit for use with a tape recorder. While I don’t make any great claim to originality for the circuit, it has produced first class results over one year of interviews and might prove useful to anyone doing similar work.

Circuit diagram:
Room Recorder Circuit Diagram

The preamplifier was plugged into a Sony Cassette-Corder (any similar device will work) by means of a long, screened microphone cable and placed in a central location in a room or on a bench. The circuit will pick up every whisper, so background noise should be considered when choosing a location. A 2-terminal electret microphone picks up the sound, which is then amplified by a TL071CN low-noise op amp. Note that the microphone’s negative terminal is connected to its case. Negative feedback is applied to the inverting input through a 10kO resistor. Increasing the value of this resistor will increase sensitivity, and vice versa. For ease of use and quietness of operation, the circuit is powered from a 9V battery. The power switch is mounted on the case. The circuit draws about 2mA and would therefore give about 10 days continuous service from a 9V alkaline battery.
Author: Thomas Scarborough - Copyright: Silicon Chip Electronics