3.3V PIC PSU ...but then applying 4.5V to an IO pin OK? (for IOC interrupt)


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  1. #1
    Join Date
    Mar 2009
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    653

    Default 3.3V PIC PSU ...but then applying 4.5V to an IO pin OK? (for IOC interrupt)

    Now I'd normally use weak pullups & then switch a ground to a PIC digital IO, but on this occasion, the place where the switch is going is *very* tight for space & I could really do without having to feed 0V just for the switch. Now where the switch is going to be located, there's already 4.5V present (this with a fresh battery) ...this voltage fades down to about 3.2V as the battery life fades, so I was wondering if I could just utilise that 4.5V to feed a PIC IO pin & trigger an IOC interrupt...so in essence, I'm applying about 1.2V (max) higher than the PIC's own supply - will this cause a problem?

    Another question ...when is a high a high & when is a low a low ...for example with 3.3V supply, has anyone chec ed to see what voltage is deemed a 'high' & triggers (ie can it be less than the supply) & vice versa?

  2. #2
    Join Date
    Sep 2009
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    716

    Default Re: 3.3V PIC PSU ...but then applying 4.5V to an IO pin OK? (for IOC interrupt)

    Depending on what pic, and what pin on that pic you use... Some pic have 5V tolerant input on some pin. So check that in datasheet. Most of pin on pic have protective diode. So if you apply 4,2V, you supply voltage may increase to 3,5V.
    You can just put resistor(10K) on on input pin, to prevent this.
    Hi an Lo state of pin depending what type input it is... Eg ST, CMOS, etc... Value for each input type is in datasheet.

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