A simple circuit to test the TV remote whether it is working or not. TV remote uses Infrared LED to emit pulsed IR rays which are invisible to human eye. So it is difficult to confirm the working of IR Led of remote. This Remote Tester blinks an LED when it receives IR rays from the TV remote.
TV uses Photomodule TSOP 1738 as IR sensor. It has a Photodiode , amplifier circuit and an output transistor inside the package. It works off 5 volt DC only and gives 5 V output when it is not receiving the IR rays and sinks current when it receives IR rays. That means it gives 5V in its output pin when no IR ray in its front. It gives 0 V when it receives IR rays.
In the circuit, the output of the IR sensor is directly connected to the base of the PNP transistor. PNP transistor remains off when its base is positive and conducts when its base is negative. So when the IR sensor is in standby, the high output from it, keeps the PNP transistor off . So LED also remains off. When the Remote is focused on to the IR sensor and any button is pressed, PNP transistor conducts and LED blinks indicating that the Remote is working.
Pins of BC 557
Pins of LED