Suntan monitor: controlling UV exposure
Summary
In this article, Marian Hryntsiv, Senior Technical Documentation Apps Engineer, Renesas Electronics proposes a solution to control the amount of ultraviolet light (UV) to which the human body is exposed and therefore prevent negative consequences. The task is to inform a sunbather when to turn over (or to go home) after having received the desired accumulated dose of sunlight, using a photodiode’s current (which is proportional to suntanning intensity) as an input. The idea is to use the photocurrent to ramp the voltage on a capacitor, then use an analogue comparator to trigger a short discharge pulse on an open-drain digital output pin. The measured positive-going ramp signal is V = 0.2 V and the sawtooth frequency at maximum photodiode current is: CNT0 and CNT1 are designed to set a 30-minute full-sunlight equivalent dose. Low voltage operation can supplying a project from just one 1.5V battery anda sufficient number of digital and analogue macrocells allows the implementation of myriad useful applications.