Infrared detector (CB7814E)

This circuit was found in a Popular Electronics of the 90s. The operational amplifier admits equivalent and the phototransistor can be of any type.

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Neon Transistor Indicator (CB6696E)
Found in ancient documentation, this circuit uses a high voltage transistor of the time. Observe...
9 to 330V Converter (CB25840E)
This voltage inverter uses a small transformer. The circuit was found in the April 1995 issue of...
Octave Generator (CB25462E)
We found this circuit for musical instruments in the March 1992 Radio Electronics magazine. The...