How To Test Remote Control

Here is a useful tool to test the working of the Remote handsets used for operating TV, VCD player and other remote operated gadgets. These devices use Infrared rays pulsating at 38 kHz and the sensor used is the TSOP 1738 specially designed to sense the 38 kHz IR rays. The circuit gives beeps when it detects the pulsed IR rays from the remote handset.

About Photo Sensor:

The IR Sensor TSOP 1738 is a sophisticated Photo module with circuitry to sense and amplify the pulsed IR rays. It has a PIN photodiode and a pre amplifier stage enclosed in an epoxy case. It is 3 pin device with an active low output. That is, in the stand by state (without receiving IR rays) its output will be high giving +5 volts. When it senses the IR rays, its output turns low and sinks current. The circuit inside the photo module amplifies the coded pulses of IR rays coming from the IR LED of the handset. The photodiode is the detector of IR rays from which the signals pass into an AGC (Automatic Gain Control) stage and then into a Band pass filter. From there, the signals will be demodulated and send to the output transistor. When the Photodiode senses IR rays, the output transistor sinks current.

Features of TSOP 1738:

1. Demodulated output can be directly decoded by a microprocessor

2. Internal filter for PCM frequency

3. TTL and CMOS compatibility

4. Low power consumption of 5 volt at 5 mA. Above 5V, the device will be destroyed

5. Immunity against ambient light

6. Noise protection

7. Continuous data transmission up to 2400 bps

8. Suitable burst length of 10 cycles per second. Between each 10 to 70 cycles, a time gap of 14 cycles is necessary to reset the module.

9. The module will not respond to continuous IR rays

10. Filament lamp, Fluorescent lamp, Sunlight etc may affect the functioning of the module and may induce false triggering.

Remote Circuit Diagram:

Working of the circuit is simple. Zener diode ZD and the current limiter R1 gives 5 volts regulated power supply for the IR sensor. Normally, the output of the sensor will be high which inhibits the working of PNP transistor T1 and buzzer will be off. When the sensor gets IR rays from the remote, the output of the sensor turns low and triggers T1. It then conducts and buzzer beeps. Resistor R2 keeps the base of T1 high in the standby state and C1 act as a buffer. C2 keeps buzzer on for few seconds even if the IR ray stops. R3 discharges the stored current from C2.

 

Remote Circuit Diagram:

Working of the circuit is simple. Zener diode ZD and the current limiter R1 gives 5 volts regulated power supply for the IR sensor. Normally, the output of the sensor will be high which inhibits the working of PNP transistor T1 and buzzer will be off. When the sensor gets IR rays from the remote, the output of the sensor turns low and triggers T1. It then conducts and buzzer beeps. Resistor R2 keeps the base of T1 high in the standby state and C1 act as a buffer. C2 keeps buzzer on for few seconds even if the IR ray stops. R3 discharges the stored current from C2.

 

In addition to TSOP 1738, other sensors are also available. The following table helps you to identify the pin connection of IR modules.