We found this code switch circuit in the January 1999 Electronics Now magazine. Some of the components are integrated circuits from that era.
This is the traditional configuration of na Astable Multivibrator using two NPN ttransistor....
This treble and bass control drains some milliamperes from a 12 V supply and can be used with any...
This is a very simple configuration with a power transistor to control a DC motor from 3 to 12 V...