| 摘要 |
PURPOSE:To prevent car theft effectively without using ultrasonic waves, by giving a warning when someone invades into a car illegally and the difference between the sonic pressures inside and outside the car room comes to be lower than a preset value. CONSTITUTION:An indoor microphone 10 and an outdoor microphone 12 are arranged in a car room and outside the car room respectively, and outputs from the both microphones 10 and 12 are fed to a subtruction circuit 20 through an automatic gain control circuit 14 and integral circuits 16 and 18. The difference between outputs from the microphones 10 and 12 is found at the subtruction circuit 20, and the signal of the output difference is fed to a comparison circuit 24 through a transistor 22. The comparison circuit 24 compares the above difference and the preset value, and if the difference is lower than the preset value, it will feed a warning signal to the warning device 26. Thus, the warning can be issued by utilizing the sonic pressure difference between inside and outside of the car room, without using ultrasonic waves, to enable to prevent car theft effectively.
|
