Burglar alarm for your garden Alarm for giving
, created to protect the country house
many years ago, it proved over many years of service. Feature of its design is that it identifies undesirable approach the protected object at a distance, and does not use or operate the gap loop mechanical switch, as in ordinary common security devices and capacitive relay. Once a man approached the door closer than 1 meter, the instrument produces sound and light signals. Just this device can be applied not only to protect the cottages, but other items, such as an apartment or garage.
At low power transistor VT1 assembled generator oscillation frequency of 90 KHz. VT2 input circuit is configured on the same frequency. Closer to the sensor-grid of 0.5 x 0.5 m, we change the capacitance, thereby changing the frequency of oscillation. Circuit L2, C7 is upset, and on the basis of blocking voltage VT2 appears before VT2 open. Because of this, the collector voltage VT2 appears close to the supply voltage when a signal based on VT2 it was close to zero. This voltage exceeding the threshold zener VD3, gets on base transistor VT3 and opens it. Through the relay R1 included in the collector circuit of VT3, current flows, and the relay closes its contacts executive chain, which are call load and light bulb. Using zener VD3 in the base circuit of the transistor VT3 dramatically increases the sensitivity of the capacitive switch, and almost completely eliminates the phenomenon of hysteresis -operate and release voltage relays differ by less than 0.26 V. As the sensor uses a metal plate copper, duralumin, iron. Set it on the door from the inside, yet it can be hidden under a decorative upholstery. Just as Sensor
You can apply the doorknob lock, bolt, metal window grille. Coils L1 and L2 are the same, the wire is wound PEL-0, 15 on standardized frameworks of portable radios. 200 windings are distributed uniformly on all three sections of the frame. Inductance coils is 30 mH. T1 -anyone with an output voltage of 12V. Forging is tuning circuit L1, C4 to 90 kHz frequency. L2 circuit tuned to the same frequency. Capacitor C1 regulate sensitivity capacitive relay. Resistor R6 set on Zener voltage close to the threshold of stabilization. The position of the engine of this resistor depends on the sensitivity of the sensor security system. Wire connecting the sensor-grid with the scheme should be a minimum length. The device can be self-powered by a rechargeable battery 12 V. Call and signal lamp shall be rated at the same voltage. That would extend the capabilities of this device, you can use automatic blocking and timers to turn it off. However, even in the form in which the device is shown in Scheme, it also works perfectly, ie, capable of reliably protect doors from thieves.