In order to solve the problem of instability of illumination brightness in visible light communications,a novel coding modulation method using pulse width modulation(PWM) waveform as carrier is proposed.A transmitting and receiving module based on this method is designed.The frequencies of PWM waveform at logic 1 and logic 0 are 38 kHz and 7 kHz,respectively.A high brightness light-emitting diode(LED) was used as source,a current input preamplifier composed of a PIN photodiode and low a noise wi...