This circuit uses an optical coupler to indicate a phone call through a lamp. The circuit is from a Hands-On Electronics from the 90s. The lamp must be incandescent.
In the figure we have an interesting possibility that consists of the activation of a heating...
This circuit was found in a 1980s telecommunications publication. The circuit uses a diode bridge to...
This simple alarm was found in a 1982 documentation, but uses components that are still common,...