We are thinking of using the TAOS device (light to frequency converters and other devices) in the optic sensors but there are a bit on the expensive side. The major issue is that they do not work well with pulsed light. For optic proximity switch, the LED is always pulsed with high current (>100mA or even 300mA) and small duty ratio (less than 5%). They do work in the DC light condition. We met TAOS CEO and VP sales and marketing early this year and they have really good stuff. Later their sales representatives show us the LUX meter in a PCMCIA card format. It can even tell you the light source: fluorescent, incandescent or sunlight, etc. Xiaofan >Date: Mon, 1 Nov 2004 12:04:23 -0800 (PST) >From: "Harold Hallikainen" >To: "Microcontroller discussion list - Public." > >I think an LDR based design would be extremely non-precision. LDRs vary >considerably unit to unit, are nonlinear, and have different "light >adapted" and "dark adapted" resistances. My favorite method of measuring >light is the TSL235R at http://www.taosinc.com/category.asp?cateid=2 . >Just count the frequency. No analog circuitry on your part. > >Harold _______________________________________________ http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist