This configuration similar to many of this site was found in 1965 General Electric documentation. Modern equivalent transistors can be used. LEDs can be used.
This circuit allows you to read resistors up to 20 M ohms, converting it into voltage. The circuit is...
This oscillator was found in the January 1996 issue of Electronics Now magazine. The frequency is given by...
The S-meter is signal strength meter, coupled to telecommunications receivers to indicate the...