This circuit with the ULN3784B appeared in the October 1984 issue of Radio Electronics magazine. It can typically be powered from 9 to 24 V.
The voltages in an adjusted range in the trimpots are indicated by 3 LEDs. The LEDs indicate when...
This traditional version of astable signaling transistors was found in an American 1980s...
This circuit was found in a 90’s EDN. The components used are still common and the sensors can have...