This circuit was obtained from Motorola documentation from 1969. The setting applies to other operating systems, including lower supply voltages. The zener determines the output signal.
Found in American documentation from the 90s, this configuration detects the direction of rotation...
Circuits similar to this can be found in this section. This is from 1967 General Electric...
This circuit uses two transistors and can be powered by just two small batteries. The frequency is given...