This sensitive 5-band circuit was found in a September 1995 issue of Electronics Now magazine. The headphones, for greater sensitivity, should be high impedance.
Using bipolar, FETs and unijunction this long-lasting timer can reach 10 hours with good quality...
This 1-transistor circuit for currents up to 50 mA was found in the August 1974 Radio Electronics...
We found this circuit in a 1969 General Electric documentation. The circuit uses transistors of the...