SparkFun Forums

[brianuno]

The SparkFun experimenter kit includes a photoresistor tutorial. Two sketches are possible, one simply turns on a LED under ambient light, the other varies the brightness of the LED under changing ambient light. I noticed the slight variation in LED brightness but I was not impressed. You need sharp eyes catch it before figuring out what's happening. After thinking about what an adjustable photoresistor sensitivity may be good for I thought of one. If you want to turn on an outside light at dusk, and off again at dawn, you must adjust the sensitivity somewhere between 0-100%. It's never totally dark even hours after the sun sets. The light may never turn on if it is too sensitive. The same in reverse for daylight. On a theoretical scale of 0-100, with zero being least resistance, and 100 maximum resistance, the photoresistor sensitivity ought to be between (guessing) 25% - 75%. That brings me to my question. To make the variable photoresistor sketch interesting, why not replace the LED with a meter? I searched light meters projects and there are many across the Internet. Which digital display parts does SparkFun offer that I could use to make a simple light meter? I touched the wire leads of my photoresistor with my multimeter and I get readings between about 800 and 1900 in the 2000 ohms range. That's not a light meter, but to build a simple circuit to turn outdoor lights on and off, a light meter could be used to calibrate the light sensitivity range.