Found in a 1990s US publication, this alarm circuit detects when a light beam is interrupted. Optical resources may be used for the sensor and instead of the alarm a relay may be used.
This circuit provides a signal when dialing occurs. The circuit is powered by the telephone line...
This simple injector and signal follower employs a high impedance headset. Transistors can be of...
This circuit uses a 6-bit A / D converter from Philips, and has its output compatible with most...