Do I need clamping diodes on PIC A/D ports? - Electronic Circuits Projects Diagrams Free

William At MyBlueRoom · 14th August 2006, 04:08 PM

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

**Nigel Goodwin** · 14th August 2006, 04:20 PM

Quote:

Originally Posted by William At MyBlueRoom

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 · 14th August 2006, 04:38 PM

Thanks Nigel, RA0 has the clamps.

kchriste · 15th August 2006, 04:28 AM

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** · 15th August 2006, 09:08 AM

Quote:

Originally Posted by 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....

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

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14th August 2006, 04:38 PM	(permalink)
William At MyBlueRoom	Thanks Nigel, RA0 has the clamps. __________________ Bill Home of the Firefly PIC Tutor Inchworm ICD2 http://www.blueroomelectronics.com

15th August 2006, 04:28 AM	(permalink)
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.... __________________ --- The days of the digital watch are numbered. ---