I'm tapping the ribbon cable interface between a HVAC control board (relays, etc) and display board (membrane panel + led display) to reverse engineer how to change the set point programmatically. I came across these traces using a logic probe / oscilloscope. Small pulses are clearly occuring when keypresses occur, but I can't understand why they occur in reference to what appears to be a 60 hrz signal. My best guess is that somehow the AC line power is getting picked up by the logic probe but I can't see how since I see this pattern regardless if I ground to the chassis or a persistently zero volt pin on the wiring hardness.
Is there a serial communication protocol that looks like this? (Signal appears to be on channel 3 and 4).
Have already googled extensively for specs on a Ranco 7221081 PTAC control board and found nothing hence the need for reverse engineering.