Dear PIC Specialists,

I use a PIC16C84 based Circuit with Audio (Freqency: 100 - 1000 Hz) Input.

My problem is to construct a AUTOMATIC GAIN CONTROLLED OpAmp
(with CA3140) using only nonsymmetrical 0V GND and 5.4V Powersupply.

I need this because the input Voltage is a sinodial Wave with a variable
Amplitude of only 3 to 10 milli Volts. I want to obtain a stabilized Wave with a
Amplitude of 2 Volts whitch has about +2.5V DC Offset (will say: the Voltage
varies between +0.5 and +4.5 Volt like a +2.5V shifted Sinewave).

The Output of this should go after a Smitt Trigger in the PIC to measure the
Frequency.

Has anyone Ideas? Where I can obtain help with AGC Circuits?

Thank You for all Help,
              Bernd