Identifying and using a rotary encoder, help!

Hey everybody!

I'm trying to just understand and use a simple rotary encoder, so I can use them for bigger projects eventually. So right now I opened up a working ps/2 mouse I had and took out one of the IR LED/sensor pairs.

But I'm having trouble using them. I can't find the datasheets because they don't have P/N's on them. The LED isn't hard to use. I've found its forward voltage drop by using the meter's diode test, and in a simple battery-diode-resistor circuit. It is about 1.35V.

But the sensor is proving to be trickier. From looking at the circuit board in the mouse, I know that V+ and GND go straight to two of its terminals, and the third pin goes to one of the pins of the chip on the board.

At first I just tried running about 20mA through the LED with it the same distance from the sensor as it was on the board. I had the sensor hooked up with the appropriate pins to 4V (I know it gets 5 from the mouse but my batteries are weak) and measured the third pin with the voltmeter. No change if I blocked the LED from it or not.

I tested it straight on the board too, since there are two more LED/sensor pairs. Nothing there...can anyone help me?

This link may (or may not) help you. fpga4fun.com - Quadrature Decoder

Thanks, that's kinda helpful. I also saw on this site Recycle PS/2 Mice To Rotary Quadrature Encoders that the LED has to be pulsed...why is that? Why can't it work so it is just on all the time? And why wouldn't the circuit be working when I just hook power up to it?

Here are a couple pics. As you can see, two of the pins from the phototransistor/whatever it is go straight to the power supply, GND and V+:

**broken link removed**


**broken link removed**

edit: jesus christ, why doesn't the BB resize the images??