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Need help with ADC module of PIC - +/-5 voltages

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malik_123

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negative adc with pic

will it be ok to to allow more then +/-5 volt to appear on the Port A of PIC series microcontroller

or i should scale down the voltages before reading them


i am keeping in the mind that there is built in diode protection for negative voltages and the more then 5 volt positive voltages

thats why i have not included external diode to clip the negative side voltage

but wanna learn will it be ok not to use the external diode and to keep faith in the built in diode for the protection of ADC
 

Re: ADC module of PIC

Hi,

will it be ok to to allow more then +/-5 volt to appear on the Port A of PIC series microcontroller
Click to expand...

In a word, No.

You will need an op amp & buffer with a gain of 0.5 to reduce your +/-5v to 0 - 5v for the pics adc.

Not into that type of circuitry but plenty of examples around.
 

Re: ADC module of PIC

what problme we could face if we subject more then +5 volts and negative voltages to the ADC pins of pic
 

ADC module of PIC

If you do connect without scaling, use a current limiting resistor to save your pics input. Otherwise you could pass more current through the protection than it can handle - one useless pic.

Keep in mind that the signal will still be clamped to the range Gnd-0.6v to Vcc+0.6v, and will give a reading of 0 for Gnd (or less) and 1023 - assuming a 10 bit adc for Vcc (or more). So it will only read the positive going portion of your signal. If this is an issue you will need to scale as described by wp100.

If only unwanted (or ignorable) signals are outside of this range, then you can use the protection network to reduce complex circuitry.
 

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