Patent ID: 7948366

Claim:
A car speed alarm system installed on a car, the car speed alarm system comprising: a modulation module having a brake sensor detecting a brake action of the car; a speed sensor detecting a car speed; a microprocessor having input terminals connected with the brake sensor and the speed sensor respectively, being triggered by the brake sensor to read the car speed during the brake action, and converting the car speed into a binary signal for output; and a brake light being connected with the microprocessor to receive the binary signal and to vary in its brightness corresponding to the binary signal, and to output a binary light signal; a switch having a control terminal connected with an output terminal of the microprocessor; an input terminal connected with a power supply; and an output terminal connected with the brake light, so that the microprocessor controls the ON and OFF of the switch according to the binary signal, generating variation in the brightness of the brake light; and a demodulation module having a sensing unit comprising: a car light sensor for detecting the brake light signal from the car in the front; and an environmental light sensor for detecting an environmental background light signal; a processing unit being connected with the sensing unit to receive the input signal and determining the variation in the brightness of the brake light of the front car, the processing unit comprising two signal amplifiers respectively connected to the car light sensor and the environmental light sensor to amplify brake light signal and the environmental background light signal; two rectifiers respectively connected to the two signal amplifiers; one comparison circuit having a positive input and a negative input both being respectively connected to the two rectifiers, and comparing brake light signal with the environmental background light signal; an output processor connected to an output terminal of the comparison circuit to receive a comparison result, and having an output terminal connected with the outputting unit; and an outputting unit being connected with the processing unit to receive and output an output signal.