LDR Circuit Projects - Ideas for Science Fair

[Cyph0n]

Hey everyone,

My teacher assigned my group with working on any LDR-related (Light dependent Resistor) experiment/circuit. I haven't worked with these resistors before, so I was wondering, what kind of projects can I do? And is there something flashy that will attract people at our science fair?

Oh, and please, give me some simple ideas - nothing too advanced.

Thanks.

 

[vanesch]

The simplest thing to do with an LDR is of course a detection of the presence/absence of a light-absorbing object (say, a person) cutting a light beam. You take one or other light source that directs the beam on the LDR inside a black kind of tube (to let the LDR only "see" the beam), and if you walk through the beam, it cuts the beam and hence you have a significant resistance change (which can be used to trigger something, such as a burgler alarm).

Somewhat more sophisticated is using the LDR to position an object "halfway" the beam. If you know about feedback circuits you can activate a motor/magnet/whatever that can move the object, and design the feedback loop such that you want the LDR resistor value to be the "half-lit value". This is however much harder to put in service, but you can do more spectacular things with it (such as making the object "follow" the LDR, if you put it on a moving support).