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

[William At MyBlueRoom]

Do I need the 1N4148 diodes as seen in the schematic below?

 

[Nigel Goodwin]

Do I need the 1N4148 diodes as seen in the schematic below?

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).

 

[William At MyBlueRoom]

Thanks Nigel, RA0 has the clamps.

 

[kchriste]

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....

 

[Nigel Goodwin]

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!.