This circuit is from a 1978 Texas Instruments optoelectronics manual. The trimpot adjusts the LED current. Other currents can be adjusted if they are within the capacity of the FET.
This variable filter circuit was found in July 1975 Radio Electronics magazine. The circuit uses 3...
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
This circuit emits a warning sound when night falls. The circuit is from a Hands On Electronics from...