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> Having gnd and +5V which feed my PIC, if I add a +9V
> line, can I place a TL081 between gnd and +9V (it would
> be out of spec of 1V, but it's not the problem I'm
> asking about)

Not sure what you mean - the supply range for the TL081 is
up +/- 18V

I've just done this quick breadboard to shift your input into
the 0-5V range for the ADC. Once you decide what degree
of shift is needed you can replace the trimpot with resistors

For example with this pot (measures 9k, yuck), 1k2 wiper-
bottom and 7k8 wiper-top shifts the signal to between 0.5V
and 4.5V. You could leave it as is or calculate new values
for the bias resistors on the op-amp's +i/p

> I can't use a TL081 on the gnd/+5V power bus, and a
> dual -5V/gnd/+5V would force me to modify my already
> built PSU and, more than that, wouldn't give me the

For future reference you can make a -ve voltage with a PIC
pin and PWM


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