Legal Removal Request

Post: Thanks for being so speedy, Andrew. I checked for common ground, and it all looks okay- - no open circuits that I could find, so I'm assuming no ground loops. Good suggestion, though. I've had a few occasions where a wire is loose, on the wrong side of a screw connector. I stuck a 10-K resistor in one of the detector circuits. Output of the opto-isolator board with LED lit was 4.82 volts. Connected, the IO Pi side read 0.01 volts. Disconnected, the IO Pi side read zero. Maybe my code is faulty and I'm not initializing properly. I'm using the following code snippet to initialize the i2C: IOPi_init(ADDRESS23); // initialize io pi channel on i2c set_port_direction(ADDRESS23, 0, 001); // set bus 0 to be INputs set_port_direction(ADDRESS23, 1, 001); // set bus 1 to be INputs I then loop to read and display all 16 channels with a for() loop containing: occ_value[i]=read_pin(ADDRESS23,block_relay.occupied_pin_no[i]); and I turn one of the channels on. I get both the input and the output LEDs lit, and the voltage on the opto-isolator side reads 4.82 volts, but the test program can't see the 0.01 volt signal (which, you have to admit, makes sense because that's pretty low). I've run the test program before, using detector board output which runs 6.1 volts, and the program can see the detector signal. (No LEDs on the detector boards, unfortunately.) I worried that 6.1 volts is too high, though, so I installed those 12-volt to 5 volt opto-isolators. Hmmm... maybe if I had a smaller-rated resistor? Or, failing that, is 6.1 volts too high for an IO Pi input voltage? Just for fun, I'm going to try a smaller resistor- - say, 2 k-ohms. Please advise. Russ