Hi all, I am trying to use an optocoupler to isolate two circuits. Right now, I am trying to get a simple prototype going which uses a signal generator to drive the opto's input. On the output side, I have connected a resistor between the supply voltage (5V DC) and the output anode in the pull-down configuration. The signal generator is set up to generate a 4.5V square wave, which passes through a 330ohm resistor connected to the opto's input. So, as far as I understand optocouplers, one must bias the input side's anode with about 1.2V and 10mA (hence the presence of the 330ohm resistor). Whenever, the internal diode receives the right voltage and current, it should shine, making the optical switch connecting the output pins to start conducting. My problem, however, is that none of the optocouplers I have tried today have conducted during the on portion of the square wave from the signal generator. The voltage drop over the output pins remains at 5V. I have tried 10 optocouplers, all with the same result. I find it unlikely that they are all faulty. Its much more likely that I have missed something, I am not sure what though. The optocoupler I am using is an H11C6. I have attached the datasheet I am working from. Thanks very much for any assistance.