7.2--- SENSORS Part 2 (Filtered photodiodes and TSOP 1738 - IR pair)

Filtered photodiodes work as normal photodiodes. But we have got some problems as photodiodes give outputs even when sunlight falls on them. Thus to overcome this problem we use filtered photodiodes. Most of them have daylight blocking filter matched with 870 nm to 890 nm emitters.

A picture of the filtered photodiode and an IR led is given below.
The black one is the photodiode and the transparent one is the IR led.

just note the legs of any LED. One leg is always a little longer than the other. The longer leg denoted the positive terminal and the shorter the negative.




Now let’s go into TSOP 1738 and IR pair. TSOP 17XX is a product of Vishay Semiconductors. The TSOP17XX – series are miniaturized receivers for infrared remote control systems. PIN diode and preamplifier are assembled on lead frame, the epoxy package is designed as IR filter. The demodulated output signal can directly be decoded by a microcontroller. TSOP17XX is the standard IR remote control receiver series, supporting all major transmission codes. XX represents the frequency that it will detect i.e. for example if we want use a TSOP1738 detector we should use 38 KHz modulated IR. We can use a 555 timer to generate 38 KHz square wave.


This is how a TSOP 1738 looks like :)





Here is the circuit diagram of how to connect an IR and a TSOP1738 in 'one' circuit. It is better to use readymade modules from the market as they are already tested or else it takes a lot of time in adjusting the circuit. But I believe it is really necessary to make the circuit at least once as then only we can make it if it’s not available in the market or not allowed in competitions.

CLICK ON THE IMAGE FOR A BETTER VIEW.






We can directly connect the TSOP directly in one circuit and IR led in another which is very much simpler than the given circuit. For testing we can point a working TV remote control at the TSOP and see its output change. I even used lappy remote control for testing purposes as TV remote is not available in my hostel room :) Anyways for testing if an IR is working or not we can check it out using any camera, be it the lappy, cell phone or any digital camera. If we look at a working IR led through camera we can see a reddish-whitish violet colour bulb glowing.