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Thread: Measuring if the ground leg on LED is open or closed.

  1. #1

    Measuring if the ground leg on LED is open or closed.

    I am trying to add a secondary box to add some features to a project. Basically I have a stand alone 4 LED driver that opens and closes the negative leg of the LED to turn it on or off. I need to be able on a second arduino completely independent to measure that opening or closing and then do something else based on that.

    Is measuring current across those legs the easiest way? Im looking for probably 20-50ma of current. Is there an easier way? Can I just put an analog pin and hook it up to the resistor (180Ohm or so) and just get a reading from that? It doesnt need to be anything accurate as far as a definitive value. Just needs to know if the LED should be on or off.

    Thanks,

  2. #2
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    Describe the 4 LED driver (IC? discrete components? how do you signal it?) and how it's wired to the Teensy and the LEDs.

  3. #3
    Senior Member
    Join Date
    Jul 2020
    Posts
    469
    I need a circuit diagram to understand this fully. When asking a technical question you need to be much less vague:

    "I have a stand alone 4 LED driver" - no part number, no datasheet, nothing to go on - details usually
    are vital in electronics, so please provide a link to the datasheet for the part or product page.

    "measure that opening or closing" - measure what? exact timings? duty cycle? frequency? voltage?

    "Is measuring current across those legs the easiest way" - voltage is across, current goes through, so this
    sentence is hard to interpret.

    "Can I just put an analog pin and hook it up to the resistor (180Ohm or so) and just get a reading from that"
    Do you mean use the resistor as a shunt resistor? In that case the LED won't turn off. Or do you mean
    some other configuration - a diagram is worth a thousand words and is unambiguous...

  4. #4
    Thank you all for the help.

    I was able to get my hands on it today and I was able to trace and get the specs for the LED driver. Im able to just tap off of the pins and get the information I need.

    Thanks!

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