Filament Light Dimmer Circuit

This simple triac dimmer can be used to control incandescent filament lamps up to 200W. The circuit operates on the phase-control principle.

The main control is provided by VR1. This determines the rate at which C1 charges and hence the point along the mains waveform at which the voltage on C2 reaches the breakdown voltage  of the diac (D1), which is when the triac is triggered.

BT136 Triac pin configuration	DB3 Diac

Interference suppression is provided by R2 and C2.

This light dimmer is directly connected to mains. So be careful.

The potentiometer should have a plastic spindle.

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Infrared Remote Control Switch Circuit

Remote controls, specially cordless type, are very popular nowadays. Here is a simple and cost-effective cordless remote control circuit which is based on infrared rays.

Figs 1and 2 shows transmitter and receiver circuit respectively.The transmitter produces infrared rays that can be easily transmitted up to four metres with a special convex lens or a twin LED arrangement.

IC1 (741) in the transmitter is wired as a high frequency square wave oscillator which provides the gate pulse for SCR1. As soon as output current of IC1 flows through SCR1 (SN050 or equivalent), it conducts and enables the LED to emit infrared rays. Output frequency of IC1 can be varied with the help of VR1, which in turn varies the output radiations of the LED.

When infrared rays fall on phototransistor T1 of the receiver, it produces charge carriers at a rate depending on the rate of arrival of incident radiations at the pn junction of the transistor. The resulting emitter voltage is amplified by using IC2 and rectified by D2. The signal is amplified by T2 to drive the relay.

By vary VR2, one can match detection freguency of the receiver with transmiting frequency of the transmitter.

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Toy DC Motor Control Circuit With SPEED, INERTIA, BRAKE, CRUISING Controller

ere is a versatile project to control the speed of a small electric motor and also to bring it to a dead stop instantaneously. Provision is also made to let it cruise along at a slow speed if so desired.

The circuit is built around two of the most popular ICs : 556 and 741. IC556 is a dual timer whereas IC741 is an Operational Amplifier.

The voltage to start the motor is provided by the charge on C6. The rate at which this capacitor gets charged is determined by the INERTIA control VR4. So, to start the motor, decrease the resistance of the speed control VR1. The Motor will accelerate at a rate determined by the inertia control. If the speed control is suddenly increased to its maximum value, the motor speed will keep decreasing till it comes to rest after a minute or so. To bring the motor to rest quickly, the speed control resistance is set at maximum, and then use the BRAKE control. As the brake control is adjusted the rate of deceleration will depend upon the inertia control.

The slow cruising speed of the motor can be adjusted by varying the CRUISING speed control.

thus, the gadget has the following controls : SPEED (VR1), INERTIA (VR4), BRAKE (VR2) and CRUISING mode (VR3).

How it works?

The voltage on C8 is determined by VR1 via D1 and VR4. The voltage decreases slowly via R5 and R6 when the speed control is brought to its minimum position, but this voltage will decrease quickly via VR4 and VR2.

The switch S1 is provided to bring the brake control in circuit. When the motor is running at full speed, keep S1 open.

The dual timer 556 (IC1) functions in two modes. In the first mode it functions as a bistable oscillator producing 100Hz negative pulses at pin 5. In the second mode it functions as a monostable oscillator which is triggered by voltage pulses at pin 8. Pin 5 is connected to pin 8. Therefore the output of the timer consist of positive pulses and are available at pin 9. The width of these pulses is controlled by VR3.

Diodes D2 and D3 form an OR GATE which allows either the voltage on C6 or the positive pulse voltages of the timer (pin 9), to IC2, depending on which of two types of voltages happens to be higher in magnitude.

IC2 is the operational amplifier 741. It functions as a unity-gain voltage follower. The output of this IC is applied to the Darlington-Pair amplifier Q1 and Q2. This amplifier provides current about 800mA to operate the motor.

Setting up is very simple. Connect a suitable voltmeter to the output (pin6) of IC2. The meter should read about 1.5V. Slowly increase the speed control and the voltage on pin 6 should rise gradually to a maximum of about 12 volts. Next, set the speed control to minimum : the output of IC2 should remain at 12 volts for a minute or so. Now operate the brake control fully; the voltage on pin 6 should decrease to about 1 volt.

To check the operation of the slow cruising speed control, shut the speed control, and apply full brakes to ensure that C6 is fully discharged. Now, operate VR3 slowly. The Voltage at pin 6 of IC2 should rise from about 1 volt to 5 volts.

Ensure that Q1 and Q2 are mounted on proper heat sinks, since these are power transistors.

Note: If the voltage settings indicated above are not easily discernible, change the values of C2 and C5 to 100 microfarad temporarily. After setting up, replace the original capacitors as shown in figure.

This project can be utilized to operate an electric motor-driven toy train as well. Connect the output of Q1 and Q2 one rail and the negative terminal to the other rail. The motor connection, then, should also be made correctly to the rails.

The power supply is designed to separate the Control Supply from the traction supply by means of IC3.

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Voltage Controlled Volume circuit

his volume control circuit offers an unusual approach to the well-known problem of distortion in active-device attenuators. The zero-output in this case is obtained by allowing equal signals of opposite phase to cancel each other.

The input transistor operates as a ‘concertina’ phase-splitter, producing equal-amplitude opposite-phase voltages at its collector and emitter. The two signals can be brought into complete cancellation, at the summing point, by means of preset p1. The harmonic content of the two signals is very small, but not quite identical.

There will therefore actually be an even smaller distortion output at the nominally ‘zero’ point.

If something now happens to the amplitude ratio of the signals at the summing point, there will be output passed to the buffer-stage. The necessary unbalance is achieved by means of the JFET and capacitor C2. The gate bias on the FET is set by the DC control voltage applied to point A. With this voltage close to zero the FET will be cut off, so that the above mentioned cancellation takes place. As this voltage is increased there will come a point at which the channel starts to ‘bleed off’ AC collector current from the splitter; this will upset the  balance and so cause an output signal to appear. The more conductive the FET, The more output. Unfortunately, the more channel current there flows the lower will be negative gate bias and so the greater will be the distortion of the ‘regulated’ summing component.

The trick is now to employ only a moderate degree of unbalance – so that the FET operates at low distortion percentages. The process is helped also by the always present ‘clean’ summing component. The buffer stage provides gain, so that a sufficient output level is obtained. The Circuit’s frequency response extends from 50Hz to 35kHz (-3dB points). The input voltage should be limited to 100mV p-p: the output can be varied from ’0′ to 1V p-p (by using the appropriate range for the control voltage at A).

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Bass Treble Tone Control Circuit

Bass and treble circuits can be combined to form a two control tone adjust circuit, as shown here.

VR1 for Bass Control

VR2 for Treble Control

Bass and Treble controls of about ±10 dB boost or cut. It should be useful in a wide variety of situations.

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This circuit can be used for staircase lights or for any deviced which may require to be controlled from several different locations.

NOTE:

• 12 volts positive line connect to R2 and RL1 common line, Other to GND line.

IC 7493 is wired as a bistable multivibrator here.Transistor T1 (SL100 or AC127) acts as a switch for the load.

When there is a current to the base of T1, it will conduct and activate the relay which can be a 12V, 200-ohm or 9V 200-ohm type.

VR1 is adjusted to get exact 5V at pin 5 of IC 7493.

Any number of push button switches can be connected in parallel to points X and Y.By just pressing any of these switches, the circuit works and the relay operates. The lamp will glow to confirm the switching.

When any of the parallel switches is pressed once again it will switch off the supply to the lamp automatically.

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Usually a soldering iron takes a couple of minutes to get adequately heated up to melt the solder,after which the heat generated is much above the requirement and is wasted. Moreover, excessive heat decreases the life of the bit and the element, causing serious damage to the delicate ICs, capacitors and PCB tracks.

A common solution to this problem is to use a diode in series with the mains and the load, so that the iron gets only half the AC cycle. But this process has one serious drawback, that it slows down the normal rate of heating. Thus, after switching  on the power, one has to wait for a long time to start work. This can create a lot of annoyance especially when one is in a hurry.

The circuit described here solves this problem in a simple and inexpensive way and can be used with various types of loads of up to 80 watts. As the mains is switched on, an approximate 15V drop of the positive half cycle across R5 is detected and supplied to T1, which acts as a voltage regulator.

Zener diode D6 together with diode D4 (yellow LED) stabilises the emitter voltage of T1 at 13.2V DC which is then delivered to the relay circuit built around T2 and C3. Capacitors C3 charges through the base-emitter path of T2 and causes the relay to actuate. which in turn allows both the half cycles of the AC mains to flow through diode D3 and R5 to the load to heat it up at a normal rate.

After a certain lapse of time (about 2 minutes preset ), C3 saturates and T2 stops conducting through the relay, thus switching on series diode D2 to allow only half of the AC cycle through the load.

After switching off the system, C3 discharges very slowly through R3 and R4. Before C3 gets completely discharged, if the power is switched on again, C3 takes a shorter time to reach the saturation level, thus switching series diode D2 much earlier than the preset time to prevent double heating of the load.

However, if the circuit is switched on only after a few seconds of switching off, C3 gets no time to discharge and the relay does not actuate at all. MOreover, if the relay circuit fails due any reason and T2 does not conduct, no harm is done to the load because in that case D2 remains in series with it. Thus the circuit offers complete protection to the load.

As stated earlier, the given value of C3 gives a delay of 2 minutes. However, a 1000µF capacitor can also be used to produce a 41/2 minutes delay. R5 maintains a drop of about 15V across itself. So, for use in different load conditions, its value changes as shown in table 1.

The whole circuit can be mounted on a PCB and fitted in an adapter case (7.6cm *5.1cm * 6.4cm) and used as a mains plug. Since R5 gets heated up during the operation, it should be kept well isolated from other components.

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]]> http://www.electronicecircuits.com/electronic-circuits/auto-heat-limiter-for-soldering-iron/feed 4 http://www.electronicecircuits.com/electronic-circuits/touch-controlled-amplifier http://www.electronicecircuits.com/electronic-circuits/touch-controlled-amplifier#comments Sun, 09 Aug 2009 16:00:11 +0000 admin http://www.electronicecircuits.com/?p=255

Touch Volume Controlled Amplifier Circuit

Nowadays touch control techniques are becoming quite popular. They give better appearance to the control panel and are silent in operation. The circuit described here enables to control volume of the amplifier by simply touching corresponding touch pads. As there is no mechanical contact it is superior to the normal potentiometer type control. Its response is similar to the logarithmic response of human ears. It gives visual indication of the volume level by means of a single LED.

The heart of the circuit is a CMOSE IC CD4007 which comprises a dual complementary pair of MOSFETs and an inverter. It is not generally used in digital applications. Its Pin configuration is shown in Fig.2 and the complete circuit diagram of the system is shown in Fig.1. Two separate n-channel MOSFETs, T1 and T2, are used in this circuit. T2 acts as a voltage controlled attenuator and the control voltage is provided by T1. Gate to source voltage of T2 determines its drain to source resistance (Rds). It can be varied in the range of a few hundred ohms to several mega ohms.

TBA810 IC Top View	TBA810 Connection Diagram

Now, consider the circuit operation. Initially there is no charge on C1 and Rds of T1 is maximum. So T2 gets full voltage and all the input signals appear across R4. Hence, the volume level of the amplifier is minimum. As C1 is charged by touching points A and B, the Rds of T1 decreases and volume increases as the control voltage of T2 decreases. Input resistance of T1 and T2 is of the order of 10¹² ohms. So, the charge on capacitor C1 is hardly affected for an hour or two and the operation is stable.

Here IC1 is used as a power amplifier capable of delivering up to seven watts tms. However, for higher amplification any power amplifier having low input sensitivity may be used.

CD 4007 IC Top View

For setting VR1, short points A and D momentarily, provide input signal and adjust VR1 for maximum output. C1 should be a non-polarised polyester capacitor and its leakage current should be minimum. Gate and source (pin nos. 6 and 7) of  T1 are physically close, so even dust particles will form discharge path for C1. This should be avoided. Finally, capacitor charging rate can be increased or decreased by changing the value of R1. It also depends upon personal touch and skin resistance.

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555 Timer With On Off Delay Circuit

Here is a timer circuit using common IC 555. The circuit is designed to facilitate time adjustment of both charged and discharged states of the relay.

The circuit uses IC 555 in astable operation. Separate delays for charged and discharged states of the relay are achieved by using two diodes (D1 and D2) and two potentiometers VR1 and VR2 provide control over the ‘on’ and ‘off’ stages of the relay, respectively.

The circuit with given values of VR1, VR2 and C1 provides time periods that are adjustable between a fraction of a second to about one-and-a-half minute approximately.

IC 555 used should be in good condition (preferably a new piece); old ICs can sometimes give wrong results. And capacitor C1 should be of a good make, such as ‘Keltron’ ,’Uptron’ , ‘philips’.

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Water Tank Level Indicator Circuit Diagram

Simple, two-wire, remote monitoring unit,Three-LED level display, 9V battery powered Circuit diagram:

Its purpose was to remotely monitor the water-level in a metal tank located in the attic by means of a very simple control unit placed in the kitchen, some floors below.
Mains requirements were:

* No separate supply for the remote circuit
* Main and remote units connected by a thin two-wire cable
* Simple LED display for the main unit
* Battery operation to avoid problems related to mains supply and water proximity
* As the circuit was battery operated a low current consumption was obviously welcomed

The very small remote unit is placed near the tank and measures the water level in three ranges by means of two steel rods. Each range will cover one third of the tank capacity:

* Almost empty – signaled by means of a red LED (D3) in the control unit display
* About half-level – signaled by means of a yellow LED (D2) in the control unit display
* Almost full – signaled by means of a green LED (D1) in the control unit display

4012 NAND gate IC	LM393 Comparator IC	BC547 NPN Transistor

Circuit operation:
When the water-level is below the steel rods, no contact is occurring from the metal can and the rods, which are supported by a small insulated (wooden) board. The small circuit built around IC1 draws no current and therefore no voltage drop is generated across R5. IC2A, IC2B and Q1 are wired as a window comparator and, as there is zero voltage at input pins #2 and #5, D3 will illuminate.
When the water comes in contact with the first rod, pin #13 of IC1 will go high, as its input pins #9 to #12 were shorted to negative by means of the water contact. Therefore, R4 will be connected across the full supply voltage and the remote circuit will draw a current of about 9mA. This current will cause a voltage drop of about 0.9V across R5 and the window comparator will detect this voltage and will change its state, switching off D3 and illuminating D2.
When the water will reach the second rod, also pin #1 of IC1 will go high for the same reason explained above. Now either R3 and R4 will be connected across the full supply voltage and the total current drawing of the remote circuit will be about 18mA. The voltage drop across R5 will be now about 1.8V and the window comparator will switch off D2 and will drive D1.
The battery will last very long because the circuit will be mostly in the off state. Current is needed only for a few seconds when P1 is pushed to check the water-level and one of the LEDs illuminates.

Notes:
* The two steel rods must be supported by a small insulated (wooden) board
* IC1 and R1-R4 are mounted on a small board placed near or on the steel rods support
* The two-wire cable connecting the remote circuit board to the main control board, i.e. J1 to J2, can be of any size and type (preferably thin for obvious reasons). It can be very long, if necessary.
* The circuit can be used also with non-metal tanks, provided a third steel rod having the height of the tank will be added and connected to pin #7 of IC1, R3, R4 and J1.
* The 4012 chip was chosen because it contains two gates and was at hand, but you can use two of the gates contained into 4001, 4011, 4093, 4049, 4069 etc. chips, provided all inputs of each gate are tied together and all inputs of unused gates are connected to the positive rail, leaving output pins open.

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