PWM Fan Controller by LM2902N or LM324N

Description: 

This circuit is a fan controller which is using the pulse width modulation (PWM) method. It is tiny (33.78mm x 54.76mm) and easy to build. Functions of the circuit parts are listed below;

VR1: 10 K Variable resistor adjusts the fan speed.

R9:  This sets the minimum speed. With the 10k pot, a 1k resistor will give 0–100% control which is OK for model motors or lighting, 10k will give around 5v–12v range, more suitable for cooling fans.

C2: This is the timing capacitor, and with the 47k timing resistor R1 and wave amplitude control resistors R2 (22k) & R3 (10k) gives a PWM frequency of around 117Hz according to the formula

Frequency = R2 / (4 x R3 x R1 x C1)

Q1: For load currents up to about 600mA a 2N2222A NPN transistor is recommended. It comes in a TO-18 metal can.

For higher loads go for a darlington power transistor such as the TIP120, 121 or 122, rated to 5A, or a power mosfet. The IRF530 is easy to find, not expensive, and can carry up to 14A. Providing you take the usual precautions for handling CMOS, static electricity is not going to zap it. Most n-channel MOSFETs will do, look for a low RDS(on) and adequate current-handling ability. Both darlingtons and mosfets are in the TO-220 case.

Using the 2N2222A bipolar transistor you might lose 200-400mV from the 12v supply to the fan, double that for one of the darlington types; with the IRF530 I measured the loss at only 40mV with a 200mA fan.

Check the transistor or mosfet pin-outs, base or gate to R9, emitter or source to ground, collector or drain to the fan negative. A heatsink is not necessary at moderate loads. 

D1: The diode prevents back-emf from inductive loads such as brushed motors from damaging the switching transistor. With "brushless" computer fan motors it's not necessary to fit this diode across the load, as they have any needed protection already in-fan.

Click here to download the schematic, PCB and layout files

32 Channel IR Remote Controller by SL490

Description:

This is a 32 channel infrared remote controller circuit fundamentally includes key pad, decoder, transducer stage, an output and a battery. Circuit is like a pocket calculator in size. Commands are formed by using 8 x 4 matrix with 32 switches.

Be aware that only one switch functions at one time and during one command is been generating, input circuitry is irresponsive to the other commands .

Every key pad button generates 5 bit binary code and IC1 sends this code to the IR leds through D1 and D2 diodes.  Code is shaped from 6 pulses with 5 gaps. Pulse position modulation - PPM technique is used for transferring data. Data information occurs at gaps. For logic 0, long gap, for logic 1 short gap is generated

Pulse and gap lengths are calibrated by using P1 potentiometer...

Voltage Controlled Switch by BC547

Description:

This voltage controlled switch circuit operates when a voltage level which is previously adjusted is applied to the input. Circuit is designed for 24V supply but can be used in a range of 18V-36V. Voltage level which triggers the circuit can be adjusted by P1 potentiometer.  A stabilized voltage is applied to this potentiometer through zener diode and Tr5. When the input voltage level exceeds this value TR1 starts conducting and afterwards  Tr2, Tr3, Tr4 transistors conduct and  relay switches on.

Switch S1 that is connected to relay, carries the signal from Tr3 to Tr1 through R1 and keeps Tr1 conducting.

When the input is short circuited, D1 diode keeps the circuit operating and you can omit it if you want.