EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: skillz21 on October 16, 2016, 01:40:25 am
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Hi guys,
A while back, i got a pack of IR transmitter LEDs and receiver LEDs (is that even what their called?). I know i can just use the... ones with a chip built in, but i want to know what these (https://www.google.com.au/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwixs-7Ul97PAhXJnZQKHUmyDjQQjBwIBA&url=http%3A%2F%2Fwww.hw2sw.com%2Fwp-content%2Fuploads%2F2012%2F09%2FIR-Receiver-Transmitter2.jpg&psig=AFQjCNF5C3v40pAbAL2HJpRjgCTc3XF93A&ust=1476668142828878) things are used for. :-//
Thanks!
PS.Sorry for the informality in my posts :)
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How many pins do the receiver ones have?
If it has two pins it is likely a phototransistor or photodiode.
The ones with three pins contain a photodiode as well as a bunch of other magic (filters, amplifiers, demodulators) to ensure that the device receives signals that are modulated at a certain frequency, typically 10s of kHz. They will have a supply pin, a ground pin and a signal pin.
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two pins, click HERE (https://www.google.com.au/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwixs-7Ul97PAhXJnZQKHUmyDjQQjBwIBA&url=http%3A%2F%2Fwww.hw2sw.com%2Fwp-content%2Fuploads%2F2012%2F09%2FIR-Receiver-Transmitter2.jpg&psig=AFQjCNF5C3v40pAbAL2HJpRjgCTc3XF93A&ust=1476668142828878) for image.
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I am guessing the dark one is the infrared LED although it could be the other way around.
The clear one is likely a phototransistor. The longer lead is probably the emitter and the shorter one the collector. You can test it out by putting a 10k pull up resistor on the collector to a supply voltage, say 5 to 10V. Shine the infrared LED on the phototransistor and measure the collector voltage with a multimeter. Watch it drop to around 0.7V when the light is shining on it.
You can also check to see if an infrared LED is actually glowing with a CMOS camera. Although filters have gotten better these days, so maybe not. My camera phone still shows glowing infrared LEDs as purple light.