This alarm goes off if someone leaves a door open. We found it in the Encyclopedia of Electronic Circuits Volume 5 from 1995. The circuit uses components that are still common today.
Found in American documentation from the 1990s, this TTL circuit operates at frequencies typically up...
The coil L2 has 64 turns of wire 28 or thinner wire in a 1 cm form coreless and L1 10 turns on L2....
This circuit, shown in the figure, can operate from 4 to 100 MHz, based on a 2N2222 transistor or...