This car alarm was obtained in a Signetics documentation from the 1980s. The circuit uses the 555 and has a pulsed output to activate a relay that controls the horn. The sensors are parallel connected.
Old multimeters used a 22.5 V battery for high resistance measurements. If you have one, you...
This circuit has an opposite action to the previous one, triggering when light falls on the...
This circuit was found in a Popular Electronics from 1991. The transistor could be the BC548. The...