This circuit, from the 70's, can be assembled with a more modern FET like the BF245. The circuit is powered by a 9 V battery, as its consumption is very low.
This circuit shows how to control an astable configuration using the 555 IC. The control signal is...
Found in the August 1994 issue of Electronics Now, this CMOS circuit uses the 4046, which is...
This is the transmitter for the previous circuit. We found it in a 90s Electronics Now. The...