This circuit makes use of a low impedance microphone. The relay is according to the supply voltage which can be between 9 and 15 V. The operational gain is approximately 100.
We found this circuit in an American publication from the 1990s. Any FET can be used. The circuit...
This circuit can be used as an optical switch or photosensor to excite TTL logic. The transistor can be...
This sensitive circuit was found in a Texas Instruments optoelectronics manual. The transistors can be...