TR2005-098

A Low-cost Optical Sensing Device Based on Paired Emitter-detector Light Emitting Diodes


    •  King-Tong Lau, Susan Baldwin, Martina O'Toole, Roderick Shepherd, William J. Yerazunis, Shinichi Izuo, Satoshi Ueyama, Dermont Diamond, "A Low-cost Optical Sensing Device Based on Paired Emitter-detector Light Emitting Diodes", Tech. Rep. TR2005-098, Mitsubishi Electric Research Laboratories, Cambridge, MA, December 2005.
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      • @techreport{MERL_TR2005-098,
      • author = {King-Tong Lau and Susan Baldwin and Martina O'Toole and Roderick Shepherd and William J. Yerazunis and Shinichi Izuo and Satoshi Ueyama and Dermont Diamond},
      • title = {A Low-cost Optical Sensing Device Based on Paired Emitter-detector Light Emitting Diodes},
      • institution = {MERL - Mitsubishi Electric Research Laboratories},
      • address = {Cambridge, MA 02139},
      • number = {TR2005-098},
      • month = dec,
      • year = 2005,
      • url = {http://www.merl.com/publications/TR2005-098/}
      • }
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A low power, high sensitivity, very low cost light emitting diode (LED) based device for intensity based light measurements is described. In this approach, a reverse-biased LED functioning as a photodiode, is coupled with a second LED configured in conventional emission mode. A simple timer circuit measures how long (in us) it takes for the photocurrent generated on the detector LED to discharge its capacitance from logic 1(+5 V) to logic 0 (+1.7 V). The entire instrument provides an inherently digital output of light intensity measurements for a few cents. this light intensity dependent discharge process has been applied to measuring concentrations of coloured solutions and a mathematical model developed based on the Beer-Lambert Law.