"Honey, my PIC ADC pin sagged my peak detector voltage!"

[HankMcSpank]

Ok, to appraise you all, my signal path is....


audio signal in->Half wave rectifier (opamp type)-> 500R resistor-> Diode-> 4.7uf Cap (to ground)-> PIC ADC pin

(in other words a peak detect type circuit)

With the signal path above unconnected to the PIC ADC Pin, I see a nice low ripple DC level moving between 0V & 5V on my scope (ie reflecting the size of the incoming audio) ...but when I connect the PIC ADC pin up - much more ripple & the DC level only gets up to about 2.8V.

The PIC ADC pin is loading the peak detector capacitor :-(

Now I know the traditional solution would be to put a voltage follower in between the output of the cap & the input of the ADC pin, but I really don't have room for an extra opamp (yes I know they're small, but every square millimetre of my board is chocka!)


I'd have imagined that a PIC would have an ADC that's high impedance - & not loaded the cap significantly?

Any top tips/workarounds gratefully recieved as I'm presently pouring light fluid on the circuit - and if it's not sorted by midnight, it's gonna resemble a car in the main square in Cairo.