Bernd.S wrote:
>
> 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
If it's just frequency your measuring then there is a better way
with just the op amp and no schmitt
you just ac couple the op amp with a gain of 10,000
(3milli volts x 10,000 = 30 Volts).
this hard limiting will give you a nice square wave 0V to 5.4V
to feed the Pic
If you need more help email me and I'll send you a circuit
--
Peter Cousens
email: peter@cousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

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