Found in a 90s Popular Electronics, this circuit uses a 741 to generate frequencies from 0.1 to 30 Hz. Observe the phototransistor feedback.
This circuit was originally designed for the practice of Morse code, something common in 1966, the year...
This is a circuit that appears several times in this section and in articles. It is a preamplifier for...
Using the 723 integrated circuit, this circuit was obtained from an article in the August 1971...