This circuit triggers by choosing the higher of two voltages. The circuit is from a 1964 Electronic Design. The transistors are of the time and can be replaced by current equivalents.
This circuit is from the Motorola Linear Databook published in 1990. The circuit for 1 kHz can be...
This simple injector circuit can actually be powered by voltages from 3 to 9 V. The frequency is...
This stair generator uses an R/2Fl network to determine the amplitude of the steps. This circuit...