Found in 90s Radio Electronics, this small transmitter has a good range. L1 is formed by 3 + 3 turns of wire 24 around a pencil as a reference.
This circuit is from a 1980s Motorola documentation. The circuit can be made with modern...
This well-known circuit triggers a relay when light striking the phototransistor is cut off. The...
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...