> -----Original Message-----
> From: Bob Blick [mailto:bobblick@COVAD.NET]
> Sent: Friday, June 27, 2003 12:59 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: ICEPIC emulator ADC trouble
>
>
> Eisermann, Phil [Ridg/CO] said:
>
> > ADC. When the emulator probe is removed from the circuit, everything
> > operates normally. When the emulator is probe is inserted,
> one of the
> > ADC inputs jumps to 5.6V.
>
> Is the circuit under test powered from the emulator? It might
> be a power
> cycling issue, and something is latching up(although 5.6
> volts seems very
> weird!)
>

        No, it is powered from an LM340-5.

> Is the supply voltage of the inamps higher than the PIC?
>

        Yes. The in-amps are powered from 12V. they amplify a mV signal from
a pressure transducer. Under normal operation, the peak output voltage from
the in-amp is 4.3V. The resistor is to provide a little protection for the
ADC in case the in-amp output goes too high. Although it is acceptable in
this application if an overvoltage kills the ADC.

> Also perhaps try it with the computer disconnected from the emulator,
> maybe it's a utility ground problem.
>

Good suggestion. I tried disconnecting the serial cable. The amplifier
voltage dropped to 0.78V (?) I also tried running the emulator from a
laptop. the amplifier output is still 5.6V.  However, when I 'reset system'
then the amplifier output is correct.

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