Found in a 90s Popular Electronics, this sensor operates by infrared reflection. The components are modern, and the phototransistor can be of almost any type.
This configuration, which does not have a very high Q, uses a 741 operational amplifier, but other...
This circuit generates low-frequency sinusoidal signals. The variable capacitor is dual and the...
This circuit was found in a documentation of the year 1958. The transistors are germanium types...