Trying to reset, automatically, an HVAC speed control unit. The unit has an output pin H8 that goes to 24VDC when tripped, and 0VDC when running. There is no reliable ground pin (or other ground) that I can use, so I use H5, another output, which is always at 10VDC. Therefore, the differential between H5 and H8 is 14V when tripped, and -10V when running.
The unit can be reset by shorting H1 and H2 (two more pins on the speed control). H1 is always 24V.
I picked up an 8 pin Si826x opto isolator and I am having issues getting it to output anything - would like to know if I'm missing anything obvious.
Pin H8 of the HVAC speed controller is connected to a 1k resistor, and then to pin 2 on the optoisolator (anode). Pin 3 (cathode) of the optoisolator goes to pin H5.
Pin 8 of the optoisolator connected to +5V on an Arduino, and pin 5 of the optoisolator connected to GND on the Arduino. Am expecting pins 6 and 7 on the optoisolator to be at 5V or 0V depending on whether or not the HVAC speed controller is tripped. But pins 6 and 7 stubbornly refuse to be anything other than 0V, whether or not the HVAC speed controller is tripped.
I then tried connecting pins 2 and 3 of the optoisolator to more pins on the Arduino, and still no output on 6 and 7. Then repeated this with a new opto chip, in case I blew something up. Still nothing.
Am I going mad?