| Summary: | Long-term exposure to radio frequency waves can have adverse effects on human health. It may cause bad effects especially to elderly people, children, and patients with weak immune systems. On the other hand, visible light communication technologies that use a light-emitting diode (LED) light source and a photodetector to transmit and receive data through visible light have a severe demerit that the modulation and demodulation processes in the system can be complicated. This paper presents a low-cost wireless mobile indoor environment monitoring system with no additional complicated signal detecting device, except a mobile device and sensor modules. Temperature, humidity, and CO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> concentration equivalent data are collected by sensor modules, and these data are modulated using frequency shift keying modulation. The modulated data are transmitted wirelessly by using a red–green–blue LED for transmitting multiple data concurrently. An Android application is developed to act as a light-signal receiver from multiple sensor modules. The image stream of the LED is captured and is processed locally in a mobile device. A single-receiver module with a camera image sensor can accept sensing data from six sensor modules simultaneously with a maximum transmission range up to 12 m and low error rate.
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