This traditional configuration found in a Radio Shack document can use 2N2646. More keys can be added, and the power can be supplied with voltages from 9 to 15 V.
We found this circuit on Motorola's 1993 Linear Interface ICs. Equivalent operational amplifiers can be...
This circuit was found in ancient American documentation. The configuration can be implemented with...
The operating range of this circuit is 10 kHz 30 MHz. Equivalent transistors can be used. The...