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 . The four points Chou, 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 oscillation frequency of the circuit is different and the speaker tone is also different.