This circuit was found in the March 1997 Electronics Now magazine. It uses a common analog indicator and the transistor is a general purpose one.
This circuit with integrated TTL 7400 has a good teaching purpose, drawing one of two LEDs. The...
The preamplifier using JFET presets a high input impedance and very low distortion. The input...
The figure shows how to generate a sinusoidal signal using 4 flip-flops. The circuit is from a...