This sensitive bio-monitoring circuit was found in the December 1984 issue of Radio Electronics magazine. The circuit is powered by a 9 V battery and uses a low-impedance headphone output.
This is the basic operational amplifier configuration for gain 10. R2 can be changed to other...
This circuit uses a capacitor that depends on the frequency of the crystal. We found it in a 1967...
The crystal frequency of this circuit found in an American documentation is limited only by the...