internal Vref output to pin

[mr_Orange]

I am using a 18F24K80, is it possible to output the internal Vref voltage to a pin? Looking at the AD block diagram it doesn't seem possible but perhaps there is a trick to do this? I want to buffer this Vref output and use it as powersupply for a strain gauge amplifier.

[Gabriel]

*usually*.... at least on some 16F series PICs you can rout the internal Vref for the _comparators_ which is not really a _fixed_ reference but rather a very high impedance output, configurable R2R ladder...

16F's datasheet says that is intended for testing purposes but _properly buffered_ you can use it as a basic DAC.


G.
_________________
CCS PCM 5.078 & CCS PCH 5.093

[temtronic]

If you're designing your own s/g amplifier, I found out that using them in constant current mode gave 1-2 orders of magnitude better results compared to constant voltage mode. That was 10-15 years ago, maybe chips have changed but the more stable and accurate the frontend is...the better the overall system will be.

hth
jay

[Ttelmah]

Normally the Vref, is nothing to do with the ADC. The only connection is that the value is often fed as one 'input' to the ADC multiplexor. It comes from, and is used by the comparator block, and is usually described in a section just after this, so this is where you need to look to output options.
Couldn't look up for your chip, since as far as I know, there is no such chip as a 24K80. 2480, yes. 24J80, yes 24K50, yes, but no 24K80. On the 2480 for example, the CVref signal can be output on pin A2.

Best Wishes

[mr_Orange]

You are right, it is a 18F25K80 (18F66K80 family). Looking at the comparator voltage reference module I see that it is easy to output the programmable voltage reference to pin RA0.
For this project a very high accuracy is not necessary but it won't hurt so I will also look into the constant current mode.

Thanks,

Bert