• Any luck with the example tutorial in #2 post?

    'Am I explaining this right?'

    It appears so, but there are a few gotch'as

    'take a wire and short two connectors on this circuit'

    Are we truly just grounding, pulling a high voltage through it's internal pull-up to ground, or even connecting two high voltages together? What are the voltages? The MDBT42Q is not tollerant.

    http://www.espruino.com/MDBT42Q

    While there is an internal resistor, it would be safer to verify.

    See p.151

    http://www.espruino.com/datasheets/nRF52­832_PS_v1.0.pdf
    20.4.1 GPIO Electrical Specification


    'using an intercom'

    That could be powered by a 9V battery or even 12V or greater. It might be setup with protection circuitry, it might not. I smell smoke if not sure. Do you have resistors in the 5K to 10K to 50K range to use as a jumper to test? If that is successful, then a lesser chance of damaging the GPIO pin when used as an input.

    While it is quite possible under the assumption we are just grounding a pin, if one is not ABSOLUTELY sure, I'd play it safe and toggle a 1 cent transitor, which should protect the MDBT42Q and one could then control the resistors/current/grounding of an external circuit. Not enough information for me to make a suggestion.

    Review the #2 post example, it seems to be what the project requires.

  • @Robin thank you so much for your response.

    I completely agree that using a transitor would be the right way to go. It's also what @allObjects is suggesting (thanks!). If I understand correctly I would connect G to the ground, S to the connector on intercom I want to ground and D to one of GPIO of MDBT42Q. Than I would control it with a code like analogWrite(TRANSITOR_D, 1) to close circuit and analogWrite(TRANSITOR_D, 0) to brake it again. Is my understanding correct?

    The only problem I have with this approach that I don't have a transitor at hand :) and if I order one online I will have to put my project to a shelf for a week or two until it's delivered.

    I measured the voltage between the circuit I need to short using universal meter. They show 0.6V of difference. And it really looks like unlocking is just triggered by grounding this wire. If I understand correctly this means "pull-down" signal, right?

    I reviewed the tutorial with the loop and detecting when it gets grounded. I guess it's slightly different than what I need. The tutorial detects that the voltage has dropped. However in my case I need to cause the voltage to drop and the voltage is supplied by the external source (transformer coil of the intercom). Can you please elaborate on how I could cause a voltage drop on a wire connected to GPIO?

    Do you have resistors in the 5K to 10K to 50K range to use as a jumper to test?

    I don't. But I do have a universal meter. What should I test for?

    Btw, you've probably already noticed I have very little knowledge about microelectronics. I write software for living. This is my toy project to learn something outside my field of expertise.

    Thank you again for helping me out.

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