Found in an Electronic Design and 1970s, this circuit uses transistors of the time. The transistors can be replaced with equivalents and the relay is 12 V depending on the power supply.
This circuit operates with an AM radio tuned to or near 900 kHz if there is a station at this...
This circuit was found in a 1965 General Electric documentation. SCRs and unijunction may be...
Found in a 90s Popular Electronics, this circuit uses a simple 9 V source. The power can be used...