16f676 ADC voltage problem

[Ali_54]

Hi guys,
I tried 16f676 with adc. I think it should work as a voltmeter. So ıt should have high impedance (adc pin). But 16f676 conduct excess current. How can I solve this problem?
_________________
Ali ÇAKIL student at Sakarya Univercity
my department:
eletrocity electronical engenieerings
(in Turkey)

[Ttelmah]

Buffer it.
Unity gain op-amp.
The ADC on the PIC is electrically seen as a resistance, in series with a capacitor, which is then paralleled by a small current sink. The actual voltage measurement is made across the capacitor, and the drive impedance needed to ensure that this charges to within a fraction of a bit of the 'real' value, despite the current sink, is typically in the order of 1 to 2KR.
The PIC ADC, is not really that suited for used as a voltmeter. Only 10bit resolution, when even quite cheap voltmeters manage better than this. Also you need to add external circuitry for ranging. However the ADC is faster than most cheap voltmeters (most of these use dual slop integration timing to give the conversion, and typically take 1/4second to do a conversion).

Best Wishes

[Ali_54]

Thanks my friend. I solved it.
_________________
Ali ÇAKIL student at Sakarya Univercity
my department:
eletrocity electronical engenieerings
(in Turkey)