We found this circuit in a 1991 Hobbyst Electronics. The circuit makes use of an unusual transducer today. It is a piezoelectric buzzer that can eventually be replaced by an equivalent configuration.
This circuit makes use of a special LM195 power transistor not very easy to obtain. The circuit is from...
Found in documentation from the 90s, this circuit can employ other comparators in the series such as...
Suggested by Philips in a 1970 publication, this circuit uses components from that time. No...