Which photo-interrupter are you using, what is it detecting (ties, segmented disk) and what other hardware or software is counting?

Have you also considered an optoelectronic sensor, possibly a mouse with a different lens that can focus at 1cm-2cm rather than a few mm to detect movement?

I put my purchase through for the r-pi this morning, strange though since I had already put in an order I thought but maybe all those orders were reset, that or a second unit is on its way... Either way I should now have a r-pi by the middle of the month.

I also ordered a 18v7 simple pololu speed controllery so I'll be able to start testing how useful it really is.

Optoelectronic sensors do seem expensive, I keep waiting to hear you've found a cheap way with laser mice and new lenses to focus a few cm out. :)

I think I only have one on order, but I think my CC was charged back on release night and when I 'finalized' an order the other week it was charged that time for sure, so maybe there's two on the way?... I've heard the gpio's are fragile, the 3v3 is a direct line to the r-pi's core. On my ARail thread I posted my 'schematic' for my wiring plans. I'm expecting to fry a r-pi at some point, but for the first few weeks I'll just be doing motor control and rfid, nothing risky, no gpio probably, so hopefully if/when the day comes the boards aren't as back ordered. Word is 75k boards will be ready by end of June.

BTW, the 'schematic' is ugly, I'm no EE and a week ago I only knew transistors acted as switches so at some point I'll probably need input on how much was left out and what protection is needed. In the end, I'd like to have a schematic people can download that has the pin lineups for aristo's DCC plug, a 2803 chip for toggling lights and smoke, some circuits for ditch and mars lights, and a header that can connect to a r-pi or arduino so people can drop a board in and have custom control of the locos.