[hwerner]

I am looking for a schematic or at least some information that can tell me what kind of a signal is required for a 60's-era Bridgeport Textron DRO unit. I have a y-axis unit working nicely and would like to design the electronics to adapt an Acu-Rite scale reader (+5V) to work for the x-axis. Getting the +5V supply is easy, the difficulty is understanding the input requirements. The Textron reader appears to use 4 phototransistors with about 10K nominal resistance, each feeding a comparator input through a 2.2K resistance. However, simply modulating input resistance does not produce a count.