[sdiy] micro front end?

[David Brown]

Correct.  The additional challenge is meeting the over/under voltage 
spec on the Micro.  Many are 0.3 volts so the input has to be limited 
to +5.3V and -0.3V.  On the ComputerVoltageSource I did two inverting 
amps with calibrated gain, 50% attenuation (to allow 0 to +10V 
inputs), an optional -5V offset (for +/-5V inputs) and clamping to +5 
and ground with schottky diodes and current limiting resistor.

The calibration was essential since I used the on-chip ADC which is 
referenced to the +5V and the +5V regulation is +/-5%.

Dave

At 10:34 AM 3/8/2011, lanterma at ece.gatech.edu wrote:
>You can do a lot remembering two formulas:
>
>1) Inverting config: vo = -vi Rf / Ri
>
>(input through Ri to negative op amp input, Rf from op amp output to 
>negative op amp input, ground the positive op amp input)
>
>2) Noninverting config: vo = vi (1 + Rf/Rg)
>
>(input to positive input terminal of op amp, negative input terminal 
>of op amp to ground through Rg, and Rf from op amp output to 
>negative op amp input)
>
>- Aaron