This circuit uses an optical coupler to indicate a phone call through a lamp. The circuit is from a Hands-On Electronics from the 90s. The lamp must be incandescent.
This circuit is quite simple to assemble, having been found in a traditional American publication. The...
This rectangular oscillator produces signals of two frequencies, one double the other. The circuit is...
This oscillator can generate signals up to about 10 MHz, depending on the crystal used. The...