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 from the 1974 Motorola Unijunction Trigger Circuits for Gated Thyristor. The triac...
Found in old American documentation, this circuit can divide the frequency of a signal by 2 or 3...
This transceiver is also low power, but this time, it can generate signals in the 144 MHz band. In the...