How to test photo resistors

[Vyder]

Hi im new here...

ive got a bunch of photoresistors and LEDs and hv no clue how to go about testing the photoresistors...:confused:

wud sum1 bbe kind enogh to tell me how and pl describe it in great detail as if i hv no experience whatsoever coz i dont know technical terms :oops: and stuff

-Thanx :-D

[Kevin Berry]

Not sure exactly the details, but typically a photo resistor would have a voltage applied across it, and you'd measure the change in voltage based on the amount of light shining on it.

I assume maybe you bought these surplus and are looking to see if they are functional or not? If you can discerne any part numbers that would help, or maybe post a picture?

They are really basic devices, once you know their rated voltage, resistance, etc should be a snap to rig up a battery or power supply to test them. You will need, if you don't have one, a basic volt/ohm meter, get one at Radio Shack for a modest sum.

With a few more details one of our techno-wizards I'm sure will jump in to help.

[HarryBotter]

I'm not really sure what you want to test. Photoresistors are usually used to automatically turn on or off a light or trigger some event by changing light levels. As the ambient light increases the resistance decreases.

If you want to see if that works just attach both leads of a volt meter to the photoresistor and take a reading near a bright light and one with something, like a pen case, over the photoresistor. That will give you the range for that particular one.

Harry

[wrighthobbies]

Think of a photoresistor as a variable resistor but instead of a knob you turn by hand, light controls the resistance value. A typical way of using and testing a photoresistor is to use it in a voltage divider. Wikipedia has an explanation of voltage dividers - http://en.wikipedia.org/wiki/Voltage_divider . The photoresistor can take the place of either R1 or R1 depending on the behavior you want when its exposed to light. The output of the voltage divider can be connected to a microcontroller or to a multimeter to show the varying voltage.