This shield circuit is from a 1968s Motorola documentation. The relay is according to the supply voltage. R1 can be reduced to lower trigger voltages.
This circuit was found in a Popular Electronics from the 90s. The circuit with the 555 monitors the...
Mouser Electronics is making available the SLN-IOT-GPT Integrated Development Experience, a...
This circuit uses a parallel resonant crystal to control the frequency. The circuit is from Radio...