TLP759 Optocoupler - 30V / 45mA current loop?

Discussion in 'General Electronics Chat' started by uXe, Feb 6, 2015.

  1. uXe

    Thread Starter New Member

    Feb 4, 2015
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    0
    I am hoping to be able to take a serial protocol being sent over a 30V / 45mA current loop and translate the signal to send / receive from an Arduino's serial port.

    My thoughts for reading the data into the Arduino are to use a TLP759 optocoupler and adapt the common MIDI IN circuit:

    ArduinoMidiIn.jpg

    ...since MIDI is also a current loop protocol. Obviously the values for the resistors would need to be different? I'm not certain the TLP759 is the right fit - I'm just going on the fact that it seems 30V / 45mA tolerant?

    Haven't thought ahead to sending back from the Arduino - but perhaps a MIDI OUT circuit could be adapted as well? But the 30V / 5V conflict might cause problems??

    Would be eternally grateful for any assistance!!
     
  2. uXe

    Thread Starter New Member

    Feb 4, 2015
    4
    0
    So, have had some progress on this, using an incredibly simple circuit consisting of just one 110 Ohm resistor to translate the ~2mA to 45mA current loop signal into a 0-5V voltage that can be directly read by an Arduino serial port! Like this:
    Untitled.jpg
    The problem I have now is being able to transmit a signal back on the same loop... I have thought about triggering a digital potentiometer's resistance up and down to emulate the ~2mA to 45mA protocol, or using a transistor like this - but the problem is that by grounding the loop as shown in the above circuit I don't have a current anymore on the return loop to work with!

    Am hoping for an equally simple / elegant solution for being able to talk back down the loop instead of just listening in?
     
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