Thursday, October 10, 2013



schematic diagram of light position controller which is a monolithic integrated circuit often used in passenger cars. The potentiometer in the dashboard is used to define the light beam’s elevation of the car’s headlight to a state be the car driver.
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Wednesday, October 9, 2013

LED Torch

Nowadays LED are very popular. Some are using LED lights for homes instead of CFL as LED power consumption is really low. Now I am going to introduce you a torch with a single LED bulb which gives 90 times longer service than a normal bulb when you use AA alkaline batteries. Normally general torch bulbs consumes about 1.8 Watts while LED consumes about 25 mW . Can you believe this! But the brightness is same.

The below simple circuit is design for 6 Volts supply if you want to use 9 Volts then simply change the value of the R3 resistor in to 470 Ohms.

To get best results do not use a normal LED which are available in the market use the specific one.

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Tuesday, October 8, 2013

Relay Coil Energy Saver

Some relays will become warm if they remain energized for some time. The circuit shown here will actuate the relay as before but then reduce the ‘hold’ current through the relay coil current by about 50%, thus considerably reducing the amount of heat dissipation and wasted power. The circuit is only suitable for relays that remain on for long periods. The following equations will enable the circuit to be dimensioned for the relay on hand: R3 = 0.7 / I Charge time = 0.5 × R2 × C1 Where I is the relay coil current. After the relay has been switched off, a short delay should be allowed for the relay current to return to maximum so the relay can be energized again at full power. To make the delay as short as possible, keep C1 as small as possible. In practice, a minimum delay of about 5 seconds should be allowed but this is open to experimentation.

Relay Coil Energy Saver circuit schematic

The action of C2 causes the full supply voltage to appear briefly across the relay coil, which helps to activate the relay as fast as possible. Via T2, a delay network consisting of C1 and R2 controls the relay coil current flowing through T1 and R3, effectively reducing it to half the ‘pull in’ current. Diode D2 discharges C1 when the control voltage is Low. Around one second will be needed to completely discharge C1. T2 shunts the bias current of T1 when the delay has elapsed. Diode D1 helps to discharge C1 as quickly as possible. The relay shown in the circuit was specified at 12 V / 400 ohms. All component values for guidance only.
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Monday, October 7, 2013

Battery Desulphation Progress Monitor

A number of readers have asked how to tell when the Lead-Acid Battery Zapper has done its job and battery desulphation is complete. In the author’s experience, batteries that are going to respond to this treatment will generally show quite a high peak voltage across the terminals at the beginning of the treatment. If this steadily decreases and practically disappears, then the treatment is near to complete. This may take anything from a week to many months, depending on the size and condition of the battery. In the absence of an oscilloscope to monitor the voltage peaks, a simple peak detector can be constructed from a fast diode and 100nF capacitor. Any high-impedance multimeter (eg, most digital types) can then be used to measure the average DC voltage across the capacitor.

Battery desulphation progress monitor
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Sunday, October 6, 2013

Cheap AC Current Measurement

The easy way to measure high AC currents is to use a clamp meter but these are generally quite expensive and cost several hundred dollars at a minimum. Add-on clampmeter adaptors can work well but they only work with digital multimeters which have millivolt AC resolution. This is because the output of most clamp adaptors is quite low, 0.1A = 1mV, for example. This is no good for typical cheap DMMs which have a lowest AC voltage range of 200V. This circuit can be built into a low cost clamp meter such as the Digitech QM-1565 from Jaycar Electronics. When dismantling this clamp adaptor, remove the label which has the AC range conversion factors and then undo the two screws gain access to the inside.

Cheap AC current measurement circuit schematic

The two cross-connected transistors act like low voltage drop diodes to generate a DC voltage which is proportional to the current in the primary of clamp adaptor (ie, the circuit under test). The recommended transistors are power germanium types such as ADZ16, AD162, AD149, ADY16, 2SD471, OC16 and OC28. This approach gives lowest voltage drop and good linearity, from 10 to 300A. Schottky power diodes can also be used but the result will not be as linear. To calibrate, wind 10 turns through the clamp adaptors jaws and feed a current of 20A through the winding. This is equivalent to a single turn carrying 200A. Set the trimpot to suit your multimeter, normally set to the 2V DC range. Do not calibrate for a low current otherwise accuracy at high currents will be poor.
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Saturday, October 5, 2013

3x3x3 LED Cube Circuit Diagram



This circuit drives a 3x3x3 cube consisting of 27 white LEDs. The 4020 IC is a 14 stage binary counter and we have used 9 outputs. Each output drives 3 white LEDs in series and we have omitted a dropper resistor as the chip can only deliver a maximum of 15mA per output. The 4020 produces 512 different patterns before the sequence repeats and you have to build the project to see the effects it produces on the 3D cube.

Circuit diagram

3x3x3 LED Cube Circuit Diagram 3x3x3 LED Cube Circuit diagram

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Friday, October 4, 2013

Automatic Headlight Reminder

Do you drive an older car without an automatic "lights-on" warning circuit? If so, youve probably accidentally left the lights on and flattened the battery on one or more occasions. This headlights reminder circuit will prevent that. Its more complicated than other circuits but its also more versatile. As shown, the circuit uses two low-cost ICs. IC1 is a 555 timer which is wired to operate in astable mode. Its output clocks IC2, a 4017B decade counter. IC2 in turn drives a row of indicator LEDs and also resets IC1 (after about 10s) via transistor Q2.

The circuit works like this:

When the ignition is on, transistor Q1 is also on and this pulls pin 4 of IC1 low. As a result, IC1 is held reset and no clock pulses are fed to IC2. Conversely, if the ignition is turned off, Q1 will turn off and so IC1 will start oscillating and sound the piezo siren. At the same time, IC1 will clock IC2 and so LEDs 1-10 will light in sequence and stop (after about 10s) with the last LED (LED10) remaining on. Thats because, when IC2s O9 output (ie, pin 11) goes high, Q2 also turns on and this pulls pin 4 of IC1 low, thus stopping the oscillator (and the siren).

Circuit diagram:


Automatic Headlight Reminder Circuit Diagram


That different colored LEDs are used to make the display look eye-catching but you make all LEDs the same color if you wish. Installing optional diode D1 will alter IC1s frequency and this will alter the display rate. Finally, if the lights are turned off and then back on again, the alarm will automatically retrigger. LED1 is always on if the lights are turned on. If you dont want the LED display, just leave the LEDs out.

Author: L. Marshall - Copyright: Silicon Chip Electronics

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Thursday, October 3, 2013

Efficient Fan Speed Controller

A partial solution to quietening noisy PCs can be to reduce the speed of internal cooling fans. Low-cost fan speed controllers are available, but they often employ inefficient, heat-generating linear regulators and contain no temperature feedback mechanism. This idea makes use of a readily available, cheap in-car mobile phone charger. The majority of these use common circuitry and require only minor modifications to operate as efficient fan speed controllers complete with temperature feedback. Most in-car chargers are based on the well-known MC34063 DC-DC switch-mode IC.

When used for charging mobile phones, the open-circuit output voltage is typically set to between 7V and 9V. This is achieved with a simple voltage divider across the output, the centre point of which connects to the feedback input (pin 5) of the MC34063. To make the output voltage var-iable with air temperature, first replace the upper resistor of the divider with a 4.7kΩ resistor in series with a 4.7kΩ trimpot. The lower half of the divider is then replaced with a 470Ω resistor in series with a 500Ω NTC thermistor. These values are only a guide and can be varied to suit different thermistor and fan types.

Efficient fan speed controller circuit schematic
Note that component lead length should be minimized to avoid introducing noise into the feedback circuitry. Getting the correct fan starting voltage is a matter of trial and error. The values shown on the circuit give a starting voltage of about 6.8V at room temperature but trimpot VR1 can be used to raise this voltage as necessary. The output can then rise to about 10V if the interior temperature rises sufficiently. The 4.7kΩ resistor could be reduced to 3.9kΩ and VR1 adjusted to give a lower starting voltage if the fan speed is still too high at 7V. After running for one hour or so, the fan voltage as set by the interior case temperature thermistor on my PC settled at 7.4V.

Suitable chargers are available from Oatley Electronics, Cat. No. 2D0074. They’re currently listed at $5 for two, which is less than the price of the MC34063 ICs alone! Data on the MC34063 can be downloaded from and a useful development aid is to be found at Finally, note that not all chargers have an output filter capacitor installed. Typically, this is a 220µF 10V or 16V electrolytic type. To save a few cents, the manufacturers sometimes leave this component out, relying on the mobile’s battery to perform the filtering task. If this component is missing from your charger’s PC board, it should be installed before the supply is used.
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Wednesday, October 2, 2013

Ten Band Equalizer

The equalizer presented in this article is suitable for use with hi-fi installations, public-address systems. mixers and electronic musical instruments. The relay contacts at the inputs and outputs, in conjunction with S2, enable the desired channel to be selected. The input may be linked directly to the output, if wanted. The input impedance and amplification of the equalizer are set with S1 and S3. The audio frequency spectrum of 31 Hz to 16 kHz is divided into ten bands. Ten bands require ten filters, of which nine are passive and one active. The passive filters are identical in design and differ only in the value of the relevant inductors and capacitors. The requisite characteristics of the filters are achieved by series and parallel networks.

The filter for the lowest frequency band is an active one to avoid a very large value of inductance. It is based in a traditional manner on op amp A1. The inductors used in the passive filters are readily available small chokes. The filter based on L1 and L2 operates at about the lowest frequency (62 Hz) that can be achieved with standard, passive components. The Q(uality) factor of the filters can, in principle, be raised slightly by increasing the value of R19 and R23, as well as that of P1–P10, but that would be at the expense of the noise level of op amp IC1. With component values as specified, the control range is about ±11 dB, which in most case will be fine. A much larger range is not attainable without major redesign.

Ten-Band EqualizerThe input level can be adjusted with P1, which may be necessary for adjusting the balance between the channels or when a loudness control is used in the output amplifiers. Several types of op amp can be used:in the prototype, IC1 is an LT1007, and IC2, an OP275. Other suitable types for IC1 are OP27 or NE5534; and for IC2, AD712, LM833 and NE5532. If an NE5534 is used for IC1, C2 is needed; in all other cases, not. The circuit needs to be powered by a regulated, symmetrical 15 V supply. It draws a current of not more than about 10mA.
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Tuesday, October 1, 2013

Logic PSU With Over Voltage Protection

A simple 5 Volt regulated PSU featuring overvoltage protection. The 5 volt regulated power supply for TTL and 74LS series integrated circuits, has to be very precise and tolerant of voltage transients. These ICs are easily damaged by short voltage spikes. A fuse will blow when its current rating is exceeded, but requires several hundred milliseconds to respond. This circuit will react in a few microseconds, triggered when the output voltage exceeds the limit of the zener diode. This circuit uses the crowbar method, where a thyristor is employed and short circuits the supply, causing the fuse to blow. This will take place in a few microseconds or less, and so offers much greater protection than an ordinary fuse.

If the output voltage exceed 5.6Volt, then the zener diode will conduct, switching on the thyristor (all in a few microseconds), the output voltage is therefore reduced to 0 volts and sensitive logic ICs will be saved. The fuse will still take a few hundred milliseconds to blow but this is not important now because the supply to the circuit is already at zero volts and no damage can be done. The dc input to the regulator needs to be a few volts higher than the regulator voltage. In the case of a 5v regulator, I would recommend a transformer with secondary voltage of 8-10volts ac. By choosing a different regulator and zener diode, you can build an over voltag trip at any value.
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