multi-tone alarm

　　　　multi-tone alarm

　　Shown is a multi-tone alarm. This circuit uses the NE555 time base circuit to form a multi-tone alarm , which can monitor points a, b, c, and d at the same time. Chou, the four points b, c, and d are connected to the ground wire with wires. The J detection lines can be set in different positions. When the four points a, b, c and d are all short-circuited to the ground, the NE 555 circuit stops vibrating and the speaker is silent. When an intruder breaks any of the protection lines, the potential of this point rises - the corresponding diode is turned on, the NE555 circuit starts to vibrate, and the speaker sounds an alarm. For different monitoring points, the circuit oscillates at different frequencies and the speaker tones are also different.