Opto-Alarm System
Approx construction cost US$40 (plus $6 for optional buzzer)
The Opto-Alarm is an optically balanced light alarm for general purpose security applications. The alarm is
triggered by increasing the light level to a light-dependent resistor (l.d.r.), via a focusing lens assembly. This assembly only accepts a narrow field of light to the l.d.r., thus increasing sensitivity, to allow specific object protection and minimise false alarms.
Alarm activation occurs when the light level increases rapidly, varying light levels from cloud movement, 50Hz mains flicker from fluorescent lamps, dusk-to-dawn light changes and total darkness situations, will not cause false alarms. An optional Entry alert facility is also included to give a 30 seconds warning that you must deactivate the system before proceeding any further. A two-tone pulse is produced which sounds for approximately 11 seconds, giving enough time to "cancel’’ the alarm. If the alarm is not deactivated
(reset), the main siren will "sound-off’’ once every 2.5 seconds for 11 times, after which the system will automatically reset.
More details on this construction project can be found in the November 2000 issue of EPE Online, the world's first web-delivered electronics and computing hobbyist magazine.
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