Hi peeps,
    Can anybody throw any light on this problem I have? I am using the ADC
on a PIC 16C77 and I am having problems with readings that 'float' around
+/- 2 of a central value in subsequent conversions. A simplified circuit is
shown in the attached diagram.

I have 4 of these connected to A0,A1,A2 and A5, with VRef on A4 being taken
from one of the emitter outputs. I cycle around each of these taking a
reading. The transistor is there because I will have any number of channels
of 4 attached and I will select which bank I want with the output from a
counter or the pic itself. But for now it is tied to +5V.

Now the problem goes away if I remove the diode from the circuit. But I need
one there as I shall have multiple copies of this connected to each 'A' pin.

Now my analogue electronics knowlege goes as far as 'never stick your tounge
in a plug socket' so I am at a loss to explain why this should happen.

If anybody can explain to me why this happens, but most importantly how I
can fix it I shall be very gratefull.

thanks a lot
Catchy.



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