alarm

An alarm which gives its alarm signal at certain repetitive times, does not need to know what the actual time is. It is sufficient if it can measure the time between the alarm time points (for instance 24 hours). An electronic alarm which operates according to this principle, is less expensive than a digital clock with-added alarm. The circuit described here is an independent unit, but it can be combined with an electronic or electromechanical clock. With a switch, alarm intervals of 6, 12 or 24 hours can be set. Thus the apparatus can also be used as an aquarium time switch, among other applications. The switching off of the alarm signal is carried out by hand, or occurs automatically after 10 minutes. In addition to the alarm signal, second, 10 minute, and hour impulses are also available.