Hey everyone!

This project describes how to build an IR remote control extender/repeater to control your electronic appliances from a remote location.

An IR detector module receives IR signal from remote control and two IR LEDs are re-emitting the signal to the appliance. You can place the IR emitting LEDs close to the device you would like to control using some wire and keep the main unit close to the remote control location. The circuit consists of three main parts, the IR receiver module, a 555 timer configured as an oscillator and the output/emitter stage. We will describe the circuit operation below.

Step 1: Components Required

R1 = 1k

R2 = 3k3

R3 = 10k

R4 = 15k

R5 = 4k7 trimmer

R6 = 2k2

R7 = 470R

R8 = 47R – 1/2W

C1 = 47uF – 16V

C2 = 1n - polyester

C3 = 100uF – 16V

C4 = 47uF – 16V

Z1 = 5V1 zener

Q1 = BC549C

Q2 = BC337

IC1 = NE555

LED1 = red LED

LED2,3 = IR LED

IR receiver = TSOP138 or IR38DM

Step 2: Circuit Description

IR signal is received by TSOP1738. TSOP1738 is an infrared receiver at 38KHz. At the output of the infrared receiver, we get a demodulated signal that means we get the low-frequency control pulses. The infrared receiver is powered from C1, R1 and Z1 that forms a 5V power supply. With no signal received, infrared detector output is high and Q1 is on, so pin 4 of IC is LOW and 555 timer is in the reset state. Q1 also acts as a level shifter that converts the 5V signal of TSOP1738 to 9V signal for IC1.

When HIGH control pulses are appearing on TSOP1738 output then timer 555 (which is configured as an oscillator) starts to oscillate are a preset frequency, for the duration of each data pulse. That means that at pin 3 we get a signal that is similar to the modulated source signal. It has a carrier component and a control pulses component. The oscillating frequency of 555 timers is set by R4 and C2 and the pulse period is given by:

T = 1,4 R4 C2

Trimmer R5 is used to fine-tune oscillating frequency at 38KHz. That’s equal to the carrier frequency.

The output stage is formed from R6, Q2, one red LED, two IR LEDs and two current limiting resistors R7 and R8. Q2 is connected as a voltage follower, that means when the base of Q2 is HIGH transistor is ON allowing current to flow through LEDs. LED current is set by R7 and R8 according to the formula shown in the image above.

So IR LEDs are emitting a signal that is similar to the signal received by TSOP1738, that means it repeats the signal received at higher infrared radiation intensity. The red LED is used as an optical indicator of the output signal. The circuit can be powered from a 9V battery.