IR encoder from a ball mouse

I was a bit curious to see how an old mouse worked to be able to use the phototransistors in there for other DIY purposes. This video is shot with an old sony DV camcorder and shows how the IR shadows penetrate the receiver phototransistors.

Here is the video:

The quaderature signal output from the two phototransistors is then something like this:

A: __|--|__|--|__|- 
B: _|--|__|--|__|--



The direction of rotation is determined by the phase difference of the pulses. This would then be the other direction:

A: _|--|__|--|__|--
B: __|--|__|--|__|- 

 Hope this is useful for someone, i have used the phototransistors for this energymeter interface.