The transistors of this circuit found in a 1965 magazine can be the BC558 and the sensitive 12 V x 50 mA relay. The other components are common.
This timer activates a relay after a time interval of up to 15 minutes has elapsed, starting from...
This circuit, which can be used on an optical link, is suggested by the Texas Instruments...
This circuit uses an MW radio tuned to around 540 kHz to detect atmospheric signals, for example, from...