• Sat 2020.05.02

    Well Hello Marek @user112057 and welcome to the Espruino community. Thank you for your interest.

    It is likely (hardware) a pull-up/pull-down issue, not enough drive current, both circuits lacking a common ground or (software) the pin mode is incorrect. There isn't enough detail provided for me to make suggestions, but uploading the schematic, lock datasheet, link to tutorial if any and the current attempted code would provide some insight as there are too many combinations to just guess.

    Might get some ideas here:



  • Thank you Robin for your response. Let me elaborate.

    I have a 3rd party circuit (an intercom). I can take a wire and short two connectors on this circuit and this triggers the unlocking action. I would like to trigger the same behavior using MDBT42Q. I was hoping I would solder two wires to two GPIO pins on the breakout board of MDBT42Q and connect them to these connectors on the intercom circuit. Than I was hoping I would issue a command and MDBT42Q would open circuit between these PINs therefore shorting the connectors and opening the lock.

    Am I explaining this right?

  • 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.


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

    See p.151

    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.


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