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 circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and...
This circuit was obtained in an old magazine from the 1970s. The circuit can still be assembled with...
This circuit recognizes a tone determined by the tuned input circuit (R3 / R4 / C2). The circuit...