This circuit with the HA2400 was found in the March 1980 Radio Electronics magazine. The circuit has digital-gain control and must be powered by a symmetrical 15 V source.
This circuit monitors the temperature of soldering irons, taking them when necessary to a low...
The traditional circuit was taken from a French magazine Radio Plans that no longer exists but can...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...