could you please elaborate on that a bit more. do you mean two leds and two photodiodes or something. please explain or giv me some link to follow. thanx
As JimB says, yes, two photodiodes, and possibly two LED's, although one LED carefully placed would be enough.
Take a mouse to pieces and have a look!, count the pins on the sensors, and perhaps even scope them to see what's happening - because they may use common pins to reduce the pin count - perhaps just two outputs, one LED input, and a common ground?.
dknguyen is right. They have 1 LED shining thru the slots at 2 photo transistors. Look at the PCB traces. The unit on one side will have 3 terminals, 1 power and 2 outputs that go to the IC chip. They put out a two phase signal.
It probably has two receivers tho, one led for a light source, and 2 receivers to give you quadrature. Check the number of leads on the IR detector, likely 3 or 4.
why the above posts did not appear before I wrote my redundant answer I have no idea. I must be losing it. LOL
I found an exception doing a dissection on a newer Logitech mouse. The sensor has +5, ground and output, and puts out a signal that repeats approximately every 10 microseconds. It looks something like this:
-_-_-----------. There seems to be more information than just pulses and the second low disappears when going one direction.