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    Protection for a micropreocessor

    Hi All,

    I'm trying to find a way to protect a microcontroller from a possible wrong input voltage( backwards mainly) in one of its inputs.

    The input works at TTL level or free volt, and the input is connected internally to a pull up resistor. When the user joins the cables (free volt)or apply a TTL input voltage ( max 5v) it works fine. If the input voltage is above 5V there is a clamping diode to suppress excessive voltage.

    The problem is when a backward voltage is applied as a TTL input.The ground of the microprocessor would be connected to an external voltage, causing a possible fault in the microprocessor.

    I could fix that problem putting a diode from the microprocessor to micro-ground and then avoid any backward TTL connection, but I will lose the free volt. Any idea??


    Please see attachment to illustrate the problem.

    Cheers,
    Winsu

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    Re: Protection for a micropreocessor

    Hi,

    And what if the user connect it to 230V AC?
    Do you feel responsible for every mistake a user will make?

    Do a standard protection, use a series resistor. Maybe 10k is good... maybe less.

    Klaus
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    •   Alt12th February 2018, 23:01

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    Re: Protection for a micropreocessor

    Hi Klaus,

    I see your point and it is true.What happens is that I know that there will be users handling 24V around ( it is the voltage that they whole system works), so we know that there will be users connecting 24V backward where there are not meant to do by mistake.

    The series resistor would connected from microporcessor to ground I guess...

    Thanks,
    Winsu



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    Re: Protection for a micropreocessor

    Hi,

    series resistor for the IOs.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. Thank you.



    •   Alt13th February 2018, 17:21

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    Re: Protection for a micropreocessor

    Hi,

    The microprocessor is failing because people connect TTL backwards. By connecting TTL signal backwards they are connecting the are connecting the ground of thr microporcessor toa potential voltage, then it is causing a fail.......



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    Re: Protection for a micropreocessor

    Quote Originally Posted by Winsu View Post
    The microprocessor is failing because people connect TTL backwards. By connecting TTL signal backwards they are connecting the are connecting the ground of thr microporcessor toa potential voltage, then it is causing a fail.......
    The floating potential you mentioned (if I took correctly) is indeed a very important point to be remarked and for that reason the inter board wirings wherever possible should have the GND as the first contact to be connected. When the connector is of the linear type for example, since we usually anchor the housing on the first or last pin of the PCB connector, by putting the ground at the both ends of the same connector, in some cases helps to ensure that the reference will be the first potential to be connected.
    --------------------------------------------------------------------------------------------------
    Part of the world that you live in, You are the part that you're giving ( Renaissance )



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    Re: Protection for a micropreocessor

    Hi,

    Maybe a suitable reverse polarity protection MOSFET instead of the diode would mean a lower voltage drop across the protection device.

    Reverse Battery Protection



    •   Alt13th February 2018, 19:40

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    Re: Protection for a micropreocessor

    Hi Andre,

    Thanks for your input. I forgot to say that the inter board wiring( device supplying a TTL output and the microprocessor input) are actually two wires and they can not be changed by any possible connector.

    The problem is that a typical user could connect a TTL signal backwards to the microprocessor and corrupting the ground of the microprocessor. If you have a look to the above attachment, by connecting TTL+ in pin 2 and TTL- in pin 1 the microprocessor will be in a non expected stated producing a fault. The idea is design something to prevent that happens...


    Cheers,
    Winsu



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    Re: Protection for a micropreocessor

    Thanks,

    They are very handy solutions, but I need to keep the volt free connections and I think those solutions would avoid that volt free connection works.



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