Found in an Electronic Design from the 90's, this circuit indicates three voltage levels by activating the LED in 3 modes: off, flashing and on for high voltage.
This circuit can be used as an optical switch or photosensor to excite TTL logic. The transistor can be...
This circuit was found in a Popular Electronics of the 90s. The output amplitude will be between...
This 80's Exar circuit has a carrier detector for frequencies up to 500 kHz. The circuit uses a...