This 1965 circuit uses a Philips 4068 tube to measure extremely small charges. The circuit has as indicator a micro ammeter and the transistors are of the time.
In the figure we have an interface using an optical coupler and the comparator LM339 or any...
This circuit for cars with mechanical breakers (contact breakers) was found in the April 1969...
This circuit can be used to show the direction of current flow in semiconductors, such as LEDs....