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.
Found in an Electronic Design from 1965, this circuit makes use of transistors of the time. The...
Found in an EDN from the 90s, this circuit uses an electret microphone. The output can be used to...
This circuit compares the input voltages by providing an output according to the curve next to the...