| A Low-cost Optical Sensing Device Based on Paired Emitter-detector Light Emitting Diodes |
| Date: | December 2005 |
| MERL Contact: | William Yerazunis |
| Author: | King-Tong Lau, Susan Baldwin, Martina O'Toole, Roderick Shepherd, William J. Yerazunis, Shinichi Izuo, Satoshi Ueymama, Dermont Diamond |
| Where Published: | Anal. Chim. Acta |
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. |
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