This circuit is suggested by Texas Instruments in old documentation. The components depend on the desired characteristics for the circuit. The power supply must be symmetrical.
With an op amp with FET, this 1977 circuit uses an LDR as a sensor and drives a relay. The relay...
This oscillator with the 4049 can generate signals up to about 14 MHz according to the article in the...
Vishay's VCNL4200 integrated circuit consists of a fully integrated proximity detector containing...