With the substance of constantly enrich and people's standard of living is increasing rapidly, and people's safety awareness continues to increase, many families and units are installed anti-theft doors and Windows, doors and Windows to ensure the security of personal and property safety has played a positive role.
However, like the Treasury, warehouse, laboratory of such important places, relying on simple anti-theft doors and Windows is not enough, you must also install burglar alarm device. Common alarm with infra-red alarm, touch alarm, burglar alarm and magnetic induction alarm, etc.; these common weaknesses burglar alarm is monitoring scope memory in dead ends, as criminals committing provides an opportunity. In order to address the dead angle monitor not problems, using TWH9250 radar detection module [1], designed a new type of Omni-directional microwave alarm no dead ends.I. composition of burglar alarm
Consider the alarm when the probe to the warning should have a sound and light alarm function, but also on the scene for camera control, so that the design of the circuit structure is used to launch on the subject of cyclic microwave antenna, you should include radar detection module, alarm IC, integrated audio power amplifier circuit, infrared camera control circuit and DC power circuit five parts, the composition of the block diagram shown in Figure 1.
Second, the burglar alarm circuit design
1. detection module TWH9250 introduction
TWH9250 is an innovative radar detection module, the module has the following characteristics:
(1) microwave tube scan launch detection distance;
(2) omni-directional detection; no dead ends
(3) power consumption may be small, battery-powered;
(4) the internal circuit adopts open-collector output terminal with flexible and can be direct drive small relay;
(5) with light kongduan and sensitivity adjustment, meet a variety of occasions;
(6) the external circuit is simple, as long as connected to the ring antenna and Terminal executing agencies, power can work.
TWH9250 module form, pin arrangement and internal circuit function block diagram shown in Figure 2.
Loop antenna transmitting microwave signal form a solid network of microwave warning, when someone in net when walking, volunteers move reflected microwave signals, in which case the microwave generator "circuit will produce as objects move in weak low frequency signal.
The signal level zoom-70dB left, into the Windows comparison circuit voltage and pulse width compared to dual differential circuit. When the confirmation signal voltage amplitude and width are set, the latch circuit to trigger, the trigger signal controlled door to count control circuit for output delay, the delay time is set to 10s and, finally, the last stage power tube collector output. To improve the stability of microwave circuit, circuit of precision, the section of the circuit from 4V and 7V regulator system separate from the power supply. The circuit in the initial power on at the time by the 40s pre stability in order to enter the detection alert, later as long as they do not power off, the circuit at any time at detection status. TWH9250 module working voltage of 12 V. The lead foot function as shown in table 1.
2, alarm IC
In order to issue a similar fire-burglar alarm sound, A2 uses LC246 alarm IC [1], and his first selected sound-that is, 8 foot power (3V), readers if you change the selected sound level, you can obtain other alarm sounds.
The alarm IC is based on the detection module provides output signal.
When someone is alarm effective detection area activities, detection module control signal output with the output of a duration of about 10s or so low level signal, the signal R1 to transistor's base electrode VT1 to VT1 is in the on-State. VT1-collector-level through R3 current limiting, VZ regulators around from 3V DC voltage to enable alarm IC A2 have electrical work, from 5 feet output analysis of the most interesting of the audible alarm signal appliances. At the same time, continuity, VT1 red light-emitting diode LED1 on system sound alarm at the same time also led to the police. If the detection range of activities, the alarm will be ongoing until the end of human activities. The circuit shown in Figure 3.Because when you first power on TWH9250 approximately 40s in steady state, in this State, the output will have low level signal outputs, in order to prevent just this powerup speakers have harsh warning sound issue, so the circuit set warm-up switch S, just open the switch power, to be pre S stable time has elapsed (available through emitting State to determine the LED1), and then close the switch S, circuit that entered the alert.
3, integrated audio power amplifier
In order to make the circuit output power is large, it is better to alert, the circuit using LM386 small power general-purpose integrated audio power amplifier [2].
His two feet to invert input, 3 feet with phase input terminals, each input on the DC-close to zero, even with the short answer, DC level will not produce too much deviation from, the use of more flexible and convenient. Design time, the integrated power amplifier with OTL receives method, the input coupling capacitor C2, C4 power decoupling filter capacitors, R7, C5 for frequency compensation circuit, to offset the speaker voice coil inductance in the high frequency of adverse effects, improved power-frequency characteristics and also to prevent high-frequency excited. Because the circuit is in the form received as OTLSo in between the output and then load a larger μ F 470 of electrolytic capacitors with C6. Between 1 and 8 foot RP2 and C3, and then adjust RP2 allows the LM386 voltage gain of between 20-200. The speaker uses 8 Ω, 5W loudspeaker.4, infrared camera control circuit
From the preceding design and analysis, when the monitoring area have the warning appears, TWH9250 detection module output low level signal, at the made of 7 feet for A2 3V DC voltage; all the way to the 3V voltage as alarm IC A2 power, all the way to the infrared camera control circuits [3], and through direct R8 to VT2 's base electrode to VT2 closed by original state to on-the relay K suck, so that the infrared camera circuits have electrical work.
5. DC power circuit
DC power supply circuit consists of power transformers, Silicon, filter capacitors, three-to-end integrated regulator 4 parts, electric circuit as shown in Figure 3.
Power transformer can be purchased directly from the market or wound, its parameter to 220V/15V, 10VA selection.
Filtering can be used with large capacitor Japan ELNA (pressure of not less than 25V) to ensure its quality. C7 to eliminate clutter of power network interference signal, the Green led for power supply indicator LED2. To prevent damage to power grid that criminals alarm system failure can be 12V battery.Additionally, Figure 3 RG RG for photosensitive resistor, when the resistance is less than 1 k Ω, the module that is blocked is not working, it can achieve "rest" during the day and the night work.
If you request module work 24/7, you can not add RG, directly to the module's R-vacant. RP1-sensitivity adjustment potentiometer, best use of WSW organic solid trimming resistor, by adjusting the size of their resistance, you can adjust the detection range of the module.Probing module external ring-shaped antenna can adopt φ 2 ~ 4mm rough copper wire production, its inner diameter 10 mm, opening up the parallel wire, and ensure the antenna 10mm erected without shaking.
In addition to the adjustable resistor in a circuit, the remaining resistance are RTX21/8W carbon film resistors.
III. concluding remarks
The burglar alarm using radar detection module TWH9250, unique design and simple control circuit, and the monitoring range is large, detection sensitivity is high, adjust the sensitivity potentiometer allows detecting distance between 1 ~ 5m.
The device in a laboratory test, running well; with simple, practical, reliable, high sensitivity.
Is a good prospect, worth promoting new burglar alarm device.【 References 】
[1] Chan Hing, xiegang. Innovative electronic module application manual [M]. Beijing: China machine press, 2003.
[2] the Tang, Song Tao's issue. Electronics [M]. Beijing: chemical industry press, 2005.
[3] Lei Xu, Ho million strong. New home burglar alarm systems [J]. Modern electronic technology, 2003, 26 (4) 82283, 86.
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