The light turns on the sound. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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The proposed device reacts to light. It is convenient to use it as a simple "guard" in a basement without windows or somewhere in a utility room (shed).
If a light is turned on in such a room, whether it be a flashlight, a candle, or even a match, the device reacts and turns on an audible alarm, which, I hope, will scare off the intruder. In addition, there are many options for using such a scheme.
When the working surface of the photoresistor PR1 is illuminated, its resistance decreases to tens and units of kilo-ohms (depending on the intensity of light), the current in its circuit increases many times, and the DA1 chip turns into an audio frequency pulse generator. Rectangular pulses with a frequency of about 800 Hz (the sound is sharp and loud) are fed through the isolation capacitor C2 to the dynamic head BA1.
The frequency and duration of the pulses are regulated by the selection of the values of C1 and R1.
To force the device to turn off (when visiting a controlled room), switch SA1 is used, which is located somewhere secretly near the door.
Instead of the photoresistor SFZ-9A, you can use devices with similar characteristics, for example, FR-117. FR764, FR765. FR75-A, SFZ-2. SFZ-4, FSK-1. To increase the sensitivity of the node, I recommend connecting a group of photoresistors (2-3) in parallel. Capacitor C2 does not pass the DC component of the voltage to the dynamic head Dynamic head - any, with a coil resistance of at least 8 ohms. Fixed resistors - MLT-0,25. capacitor C1 - KM6.
The device works stably in the supply voltage range of 5...15 V. As the supply voltage increases, the volume of the sound increases. The power supply must be stabilized.
The current consumption in the standby mode (room control) does not exceed 0,5 mA, which allows even batteries or low-power batteries (D0.26-D) to be used as a power source. In the "Alarm" mode, when sound is emitted, the current consumption increases to 30...40 mA.
Author: A.Kashkarov, St. Petersburg
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