The alarms can be designed according to the objects to be monitored, and are widely used in various industries and people's daily lives. In general, the circuit of the alarm can be divided into single-point and multi-point. The single-point alarm circuit structure is relatively simple, and only needs to amplify the signal monitored by the sensor to directly drive the sound and light alarm circuit. The multi-point alarm circuit often uses the telephone alarm system developed by the single-chip technology. When there is danger such as intrusion by outsiders, gas leakage, fire, etc., the alarm can be timely and the reliability is greatly improved. Compared with the single-point type, the multi-point application has more scopes, such as industrial and agricultural production, safety and disaster prevention, and anti-theft in disaster areas. Common electronic alarms include electronic burglar alarms, flammable gas alarms, and fire alarms. Overall scheme of the alarm The following is a demonstration of the individual circuit modules. The typical application circuit is as follows: MT5087 dialing circuit In the circuit of Figure 2-3, the row and column lines of the keyboard control logic circuit correspond to a single digit in 1-0 for the new service performance of the program-controlled switch, and there are four more keys to spare. When a button is pressed, it is determined which combination of two tones is passed. After the D/A conversion of the two groups of high and low, the synthesized sine wave is added by the adder and output from the 16 end of the MT5087. The relationship between MT5087 key value and audio is shown in Table 2-1. Power circuit design The circuit will reduce voltage, rectify and stabilize the home 220V AC to obtain a stable 5V DC. Its circuit design is shown in Figure 3-1.
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