This circuit is from the Texas Instruments operating amplifier manual. Any operational can be used and the font need not be symmetrical. Rf and Rg determine the gain of the circuit.
This alarm, from a 1996 magazine, can be fitted with two BC548s in the original configuration...
Using only one general purpose transistor this circuit is powered by batteries. The lamp of the...
Can be used as a shield, this old American documentation circuit offers digitally selected...