《MK_An optical sensing approach based on light emitting diodes》.pdfVIP

Sensors and their Applications XIV (SENSORS07) IOP Publishing Journal of Physics: Conference Series 76 (2007) 012054 doi:10.1088/1742-6596/76/1/012054 An optical sensing approach based on light emitting diodes 1 2 Radovan Stojanovic and Dejan Karadaglic 1Faculty of Electrical Engineering, University of Montenegro, Montenegro 2 School of Biological Sciences, University of Liverpool, Liverpool, L69, 7ZB, UK E-mail: stox@cg.ac.yu Abstract. An extremely simple optical-sensing technique has been developed for various applications. The proposed sensing system employs one, two or more LEDs whereby each one can be used as a light emitter or light detector. The main advantages of the proposed pulse based signal conversion technique are that it leads to better spectral sensitivity; increased and adjustable resolution; reduction in cost, dimensions, power consumption and it avoids the need for expensive and precise operation amplifiers, ADCs and other external components. The sensing configuration presented here, uses only two I/O pins of standard microcontroller, one or two LEDs and is capable of detecting various optical effects. Using multi-configurable I/O pins the LED used as a light detector is reverse biased so that the photocurrent generated by the incident light discharges its inherent capacitance throughout Hi-Z input impedance. A simple timer circuit that measures the decay-time taken