We found this circuit in the Texas Instruments optoelectronics manual. Field effect transistors can be BF245 and bipolar BC548. The sensor is a photodiode in the photo-generator mode.
When this circuit is activated the LED flashes for a moment indicating that the function has been...
This 1970 Electronic Design circuit uses a varactor or varicap. The circuit divides the frequency...
Found in a 1993 Electronics Hobbyst Handbook, this passive circuit can be used with common...