This circuit makes use of a low impedance microphone. The relay is according to the supply voltage which can be between 9 and 15 V. The operational gain is approximately 100.
This circuit was found in a 1978 publication. Equivalent operational amplifiers can be used. The...
This instrumentation circuit was obtained in the National Semiconductor's Linear Applications...
This circuit produces a sinusoidal signal whose frequency can be calculated using the formula in...