Hi,
I have a rotary encoder, labeled QEDS-7090. It came from the front panel of an HP logic analyzer. I'm trying to figure out the pinout, and I'm seeing some puzzling stuff.
I found a datasheet for another encoder that may or may not be compatible:
http://www2.ece.ohio-state.edu/~passino/encoder.pdf. If it's compatible, then the 5 pins are:
1 - GND, 2 - n/c, 3 - Channel A, 4 - Vcc, 5 - Channel B
That's plausible. The QEDS-7090 has 5 pins and pin 2 is not connected when wired into the HP LA. I measured for diodes and saw that there's a diode going from pin 4 to 1, from pin 4 to 3, and from pin 4 to 5. There appear to be no other circuits.
I understand that the diode from 4 to 1 is probably an LED. And I guess it's plausible that would I see diodes from pin 4 to pins 3 and 5 (photodiodes or phototransistors? I dunno.)
But the weird thing is, if I connect +5V to pin 4, ground pin 1, and turn the wheel, I don't get any signals on pins 3 or 5 (checking with an o'scope). Weirder still is that if I connect +5V to pin 5 and turn the wheel, I don't get anything on pin 3 but I get a nice square wave on pin 4!
It's possible that the encoder is broken; I have no way of testing it. But I can't explain why I would see the square wave on pin 4.
Can anyone help me with figuring out this wiring?
Thanks,
Bob