Using mouse IR sensors


I was trying to use the IR sensors and the optical encoder in my mouse to find my dc motor's rpm but i have run into some problems.

when i opened the mouse i saw two slotted wheels each having its own pair of ir receiver and transmitter. the transmitter was a two pin device and the receiver a 3 pin device. as far as i know the 3 pin device has one pin extra so that you can also know the direction of rotation. since i didnt need the direction of rotation, i left it open.

i connected one pin of the transmitter to the Vcc via a resistor. The other to the common ground. as for the receiver i left one pin open (explained above), the centre pin to gnd and the third pin to Vcc via a resistor and before the resistor i took the output

it looks somewhat like this

gnd vcc | | | (R) |____| (Tx)

(Receiver ) (open)__| | |_____(R)_____ | |___output | (gnd)

But the problem is that the IR fails to give any ouptut at all. I made sure i had the terminals right but i cant seem to figure what might be the problem. can anyone help?

ps: in the ps/2 mouse however the circuit was slightly different. one pin of the receiver and one of the transmitter were connected to CLK. and one pin of the transmitter was pulled low via a resistor. the remaining two pins of the receiver became inputs of the mouse controller. i tried to make that circuit too...but it didnt work. :(

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How have you tested if you have any IR output? Is there any voltage across the LED? A good test for IR can be a simple b/w video cam which usually dosen't have an IR filter (you probably already know this) otherwise, are you sure you are using the correct two pins to the receiver device? or is it a photo tranny or something and therefore needs all three pins?

Mark K.

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Mark Kelepouris

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