This circuit was found in a 90s Popular Electronics. The circuit uses components from that time, intended to receive signals in the range of 150 to 250 kHz.
This 3-component circuit uses an analog indicator. We found it in an old publication....
Pulses in sequence can be generated from a clock input using the circuit shown bellow. Outputs A,...
This circuit simulates a low-level siren and can be supplied with voltages from 5 to 15 V....