This circuit was found in American documentation from the 1960s. The operational amplifier is from that time, but the configuration applies to modern equivalents.
This LED indicator circuit uses an LM339 comparator. The circuit was found in the January 1995...
This circuit is from an 80's documentation. Equivalent transistors can be used. The circuit is...
We found this circuit in a 1967’s Electronics World. The circuit can be made with modern...