Audio visual IR sensor tester

Most of the Remote control systems use TSOP 1738 IR Sensor module to control various functions. This IR Sensor is highly sensitive and may damage easily, if is supply voltage increases above 6 volts. This tester is useful to check the working of the IR Sensor. It gives audio-visual indications when the IR sensor is working properly.

TSOP 1738 is designed to sense 38 kHz pulsed infrared rays used in remote handsets.

The IR Sensor has a PN photodiode and a preamplifier stage encased in an epoxy case. The case acts a filter and allows only IR rays to pass through it. The sensor is equipped with an AGC, band pass filter, a demodulator and a control circuit. The output of the sensor has a bipolar transistor with 80-100 K resistor in its collector. The output gives 5 volts at 5 mA current in the standby mode and the output sinks current when the sensor gets pulsed IR Rays. This sensor is capable of continuous data transmission up to2400 bps or more. The band pass filter and AGC circuits suppress unexpected noise to prevent false triggering. The sensor responds to the IR rays only if the carrier frequencyis close to the centre frequency of the band pass filter.

Fig. 1: Image of TSOP 1738 IR Sensor

The IR Sensor tester is powered by two 3 volts lithium cells. The sensor module is tested using the Test socket. Alternately you can use 3 mini alligator clips for on board testing. When the switch S1 is turned on, LED and buzzer remains off, if the IR sensor is good. When the remote handset is focused on to the sensor, and any of the buttons is pressed, LED blinks in sympathy with the pulsed IR rays and buzzer beeps. This indicates that the sensor is good.

A good sensor will give high output when it is not receiving IR rays. This high output makes the cathode of LED and the negative of buzzer high and they remain off. When the output of the sensor turns low by receiving the IR rays, LED and buzzer turns on.

3V Lithium cell