Found in an old Popular Electronics this circuit appears in other variations on this site and in this section. It uses a 7-segment common anode LED display as an indicator.
This long-time circuit uses a field effect transistor, which may be the BF245, and depends on a...
The figure shows how to implement the AND function with a Norton LM3900 operational amplifier. The number of...
This circuit is from an old documentation, but it can be elaborated with ease, since the...