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low input to microcontroller

Discussion in 'Microcontrollers, Programming and IoT' started by nges, Apr 17, 2014.

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  1. nges


    Feb 21, 2014
    hello, it seems as if i once posted something related to this but i was not really clear.
    my ideas with microcontrollers are sometimes limited, please please i really need help.

    i am trying to interface the pic16f877a with an input signal that is very very small (about 200mv). i am using an input sensor that sends one pulse of 200mv and goes back to 0v, but i know that the input voltage for digital inputs should be atleast 3v
    someone should help me tell how i can exploit this low voltage or how i can even amplify the pulse before using it at the level of the microcontroller. pls
  2. BobK


    Jan 5, 2010
    I can think of many ways to do this.

    1. Use the ADC. With a 5V reference, 200mV would read 10 counts. Accept anything above 5 as high.
    2. Use the analog comparator built in to your microcontroller to test it. Put a reference voltage of 100mV (from a divider) on the - input and your signal on the + input. This has the advantage that can be used to interrupt when it sees a high signal.
    3. Use an opamp to amplify the signal then read it as a digital input.

  3. ljcox


    Jul 10, 2010
    Or use a Comparator IC such a the LM 311 configured for threshold levels of say 100 mV & 200 mV.
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Or you could connect the 200mV to 20 inputs of the microcontroller and query the status of each pin. Surely 20 times 200mV will give you 4V somewhere, right?

    Just as if you ask the same question multiple times, you will get more and better answers.

    This unfortunately won't work.

    The one advantage you have with the PIC over this forum is that is that it doesn't have moderators and members who will get annoyed with you if you try to do something like that.
  5. nges


    Feb 21, 2014
    thanks very much Mr. Bob, i think your ideas will be very helpful to me.
    Sorry if i annoyed you Mr. Moderator or anyone else. we learn and teach others everyday.
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