Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime powered by a 6 V continuous voltage. The transistor can be a BD136.
This very high input impedance circuit is suggested by Texas Instruments. The circuit can be...
We found this circuit in the August 1994 issue of Electronics Now magazine. The circuit is based on...
This bargraph circuit using LM3914 was found in the October 1980 Radio Electronics magazine. Note...