Alarm signaling device. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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Somehow an attacker got into the habit of pulling newspapers out of the mailbox. How to catch? You can't put any buttons on the mailbox. I decided to use for this purpose a cable made of a very thin wire (0,06 mm), which is practically invisible at the entrance. The task was to some extent facilitated by the fact that the mailbox in the entrance was under the window.
The alarm circuit was made on a breadboard and located on the windowsill, and the conductors went from the outside into the gap between the window sashes.
The signaling device is a well-known asymmetric multivibrator based on transistors VT1, VT2, which is powered by a transistor key VT3 with a base shunted by a security loop. When the loop breaks, the key opens and the generator starts to work.
As a sound emitter, a capsule from Ton-2 head phones is used. In the standby (standby) mode, the generator practically does not consume current, so it can be "fed" from the "Krona" battery or an appropriate battery.
Author: A.Partin, Yekaterinburg
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