Do I need clamping diodes on PIC A/D ports?

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William At MyBlueRoom said:
Do I need the 1N4148 diodes as seen in the schematic below?
Click to expand...

No, the PIC has internal ones, although you would be advised to check the datasheet, because there are a few pins that don't (such as RA4, because it's open-collector).
 
It is fine to use the internal clamps if you are only using 1 A/D input. If you have 2 or more, when one of the inputs "clamps" then it will effect the accuracy of the A/D readings on the other pins. Atleast that was my experience with the 16F872....
 

Then don't use Vdd as the reference - which is a poor idea anyway!.
 
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