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Thread: Optically isolated 24v analogue input

  1. #1

    Optically isolated 24v analogue input

    Hello world of people cleverer than I am

    I am designing a project board where I can control various 'things' from inputs. outputs etc. optically isolating my inputs and outputs with 6N137's.
    But, I also have 6x analogue inputs. Not sure what voltage they will be covering/reading yet, but probably up to 24v.

    I have been reading up on opto-isolators for analogue signals, and it doesn't seem simple. Apparently the thinking is to use something like a LOC111 with 2x internal receivers, so that one can try and compensate for the non linear response.

    My thought... rightly or wrongly was to maybe control a voltage to frequency circuit with the incoming signal, and read pulse that optically? Maybe go super simple by using a 555 or something.
    Doesn't need super speed, so the pulses can be quite 'lazy'.

    Just wondered if anyone had any thought or ideas

  2. #2
    If i may ask... how do you guys access the pins under the 3.2 when designing a pcb? I Almost wish the 3.2 board was a little larger and all the pins on the same side.
    I was thinking of through hole pads that line up with the middle pins underneath, then heavily pre-tin the middle pads before installing it.
    Then, push fine wire/pins through the pcb from the front and solder.. hopefully they will attach to the solder on the 3.2. Not easy to check for a good connection however.

    I am considering binning those pins and adding an MCP23017 (16 pin I/O chip using I2c), and using that instead for a further 16 pins. Just seems a shame to waste perfectly good direct connections.

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