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.

1]Could not one put a scope on the output of the working scale to see what it is doing? Would also tell you if it is sine wave or ttl

2] Watch encoder resolution. Old US made scales are an inch division, all new[less than 20 yo] scales are metric

It's neither sine nor TTL. Scope shows a transient pulse + or - 500mv or so at each count. Everything at reader end is passive, so this must be feedback.

perhaps the scale type is completely different form any newer stuff. On the readers I have seen, the grating on the glass is matched to a grating on the reader head, resulting in the sensor seeing the light/dark from the light source corresponding to the grating pitch, yada yada. This would be a sine wave, and I think the old mitutoyos turned it to ttl on the head, but I could be wrong. I think the heidenhains leave it analog and let the box do the conversion.

So maybe you need to pick up the signal right from the sensors and convert it yourself to what the acurite wants to see, probably ttl. That pulse might not be useful for modern electronics, but a 2.5 volt sine that you can run through a gate and output........