We found this circuit in the Linear Applications Handbook of the 1994 National Semiconductor. The transistor must be a high voltage type and the LM3900 power supply must be symmetrical.
This code switch was found in a 1990 Electronics Handbook. It can be mounted with BC558...
In this application we use an additional input circuit to enable the logic command with keys,...
This circuit was suggested by Signetics in 1980s documentation. The circuit makes use of the...