How to calibrate LDRs (photoresistors)?

Hi Everybody,

i want to build a sun tracking system. I want to do this with four LDRs (photoresistors) as light sensor (2 for x-axis and 2 for y-axis) and two servo motors (1 for x-axis and 1 for y-axis).

I`ve bought four LDRs an unfortunatelly all four give me other results (resistance) wenn I test them with the same light source.

Do You have any idea how can I calibrate these sensors? Is it possible?

Thanks for help! Michael

put them in series with a potmeter so they get together a (pre)defined value.

I am not sure if it helps...

the measuring difference is not linear.

I've tested two LDRs. One of them I've calibrated with potentiometer, so both LDRs gave me the same resistance. When I've changed the light intensity, the resistance was different again.

Then you have to have a callibration table for all of them

This might be helpfull - http://arduino.cc/playground/Main/MultiMap -

robtillaart: Then you have to have a callibration table for all of them This might be helpfull - http://arduino.cc/playground/Main/MultiMap -

I was already thinking about sth like this but I was not sure if is a good solution. I will try it. Thanks for help!

Depending on how many of those things you’re gonna do, it might be worth looking into light sensors instead of LDRs.

bubulindo: Depending on how many of those things you're gonna do, it might be worth looking into light sensors instead of LDRs.

Could you please recommend me some light sensors? Do you think the TSL235R (http://www.sparkfun.com/products/9768) will be ok?

Rather than using LDR's, you could go with one of these:

http://www.sparkfun.com/products/99

Knowing exact time, you can then calculate the two angles you're after.

Do you think the TSL235R

Have a look through the RedRock site, thev'e been into such things for years. You might get a few ideas ??

www.redrok.com

Cheers ....... Mike B

Hi everyone, i’m a newbie with Arduino.

The calibration map code “Multi Map” seem very interesting for calibrating sensors analog inputs.

http://arduino.cc/playground/Main/MultiMap

Can anyone explain a bit more about this code with an example? (a simple tutorial will be very appreciate if possible)

Thanks in advance!

massit78:
Hi everyone, i’m a newbie with Arduino.

The calibration map code “Multi Map” seem very interesting for calibrating sensors analog inputs.

http://arduino.cc/playground/Main/MultiMap

Can anyone explain a bit more about this code with an example? (a simple tutorial will be very appreciate if possible)

Thanks in advance!

Please, create your own thread!!!

windman:

bubulindo:
Depending on how many of those things you’re gonna do, it might be worth looking into light sensors instead of LDRs.

Could you please recommend me some light sensors?
Do you think the TSL235R (http://www.sparkfun.com/products/9768) will be ok?

Actually I think this one looks a bit more interesting.

Vishay and OSRAM also have sensors… maybe you can get a sample:

http://www.vishay.com/docs/49670/pl0366.pdf
http://catalog.osram-os.com/catalogue/catalogue.do?act=showBookmark&favOid=000000020001bae400170023

Having a sensor interrupting the processor doesn’t strikes me as very efficient. :\ Although, the difference in price from the LDR to this one is quite noticeable. :\ I guess it depends on how much time you want to spend calibrating it…

I think one way is having a light bulb and use a potmeter in series with the LDR to adjust the reading at the same level of light in the room. Ok… maybe two bulbs. LOL