Hello
I want to optically isolate the computers parallel port from a motor drive circuit.
Question #1
On the ports inputs (this will be the limit switches from CNC machine) I have no +5v for the pull-up resistors on the paralell port side, thus there will not be 100% isolation. I was thinking to let the transistor outputs pull the port inputs to ground when the limit switch is closed, but while switch is not closed, I need to pull the pin high.
Is this a correct implementation of optically isolating a circuit from the paralell port, or do you suggest another method for the the inputs?
Question #2
The outputs of the parallel port is straight forward, at least I think so. The voltage from the output pin of the parallel port will source current for the LED in the optoisolator, which in turn turns on the transistor part of the isolator on. On the circuit side I can use "local" +5v to pull microcontroller pins high.
But will the current from the parallel port be sufficient to turn the LED in the optoisolator on?
Thank you!
Edit: Added a schematic to help clarifying the problem. I don't know if it does, though.
I want to optically isolate the computers parallel port from a motor drive circuit.
Question #1
On the ports inputs (this will be the limit switches from CNC machine) I have no +5v for the pull-up resistors on the paralell port side, thus there will not be 100% isolation. I was thinking to let the transistor outputs pull the port inputs to ground when the limit switch is closed, but while switch is not closed, I need to pull the pin high.
Is this a correct implementation of optically isolating a circuit from the paralell port, or do you suggest another method for the the inputs?
Question #2
The outputs of the parallel port is straight forward, at least I think so. The voltage from the output pin of the parallel port will source current for the LED in the optoisolator, which in turn turns on the transistor part of the isolator on. On the circuit side I can use "local" +5v to pull microcontroller pins high.
But will the current from the parallel port be sufficient to turn the LED in the optoisolator on?
Thank you!
Edit: Added a schematic to help clarifying the problem. I don't know if it does, though.
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