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 well-known circuit triggers a relay when light striking the phototransistor is cut off. The...
In this circuit the transistor switches when the voltage reaches the pre-set value in the trimpot. The...
This rectangular signal generator was found in an Electronics World of 1966. The transistors are...