drgeoff wrote: ↑
Tue Jan 14, 2020 7:31 pm
Change the output side of the opto:
Emitter to RPi ground.
2k2 resistor from collector to RPI 3.3 volt.
Resistor (anything between 1k and 10k) between collector and RPi GPIO.
The GPIO input will read LOW when the 24 volts AC is present.
Thanks - yeah on the second drawing I abandoned the simulated opto isolator because it was not accurately simulating the voltage drop as listed on the spec sheet. I just threw in a diode that let me tweak the numbers and thus I had no way to redraw the RBP side. My first drawing was way off.
LTolledo wrote: ↑
Tue Jan 14, 2020 9:09 pm
you just want to sense the presence and absence of 24vAC?
and nothing in between I assume
Yes - digital on or off
duckredbeard wrote: ↑
Wed Jan 15, 2020 12:24 am
I think the easiest way to do this is by using a relay. The 24V would operate the relay and the pi would look for continuity through the relay's switched output. Keep that 24V away from the GPIOs!
At first I thought of a relay however AC relays are expensive and big and I need 4 of these 24VAC inputs monitored. I considered using a 24VDC relay but I'd have to convert from AC to DC so why not try something that isn't mechanical... Based on the signals I read I will be controlling 24 HVAC damper actuators individually with several 8-channel solid state relay modules.