LDR and his scope

Other Hardware Sensors
1

Hi,
I am new to the Arduino and the sensors and all stuff. But had some stuff at scool years (YEARS) ago... hehe

I want to make a beamerlight sensor. To test the opacity of the beamerlight. If the light is to low, the light has to be changed.
I made this with my Arduino starters kit. I used the LDR and the analog input and using Processing on the PC to read out the analogread value of the sensor. So this is between 0-1023. My problem is that the value is between 20 and 100 of the sensor. This is very small comparing to the 0-1023 he can read. So i want to boost up or wathever to finetune the LDR to get between the 0-1023 when i sence the beamerlight. I know i can use a opamp...... but how?
Can anybody help me?
Would be nice......

Marcel

2

You can reduce the reference voltage, see analogReference(), select an external reference and apply a much smaller voltage to the AREF pin.

You can also select the internal 1v1 reference which may be closer to your needs.

Rob

3

Or you can change your sensor to a photo-diode or photo-transistor (I'm not sure about the difference!). It would hook up slightly differently, but not much. Plenty of help out there on the web.

Why change? Better response, wider "swing" of readings for same light level difference.

4

Thanks for the reactions.....
I think i have to use an OPAMP to finetune the voltage on the inputpin.

Can somebody help me with that?

Marcel

5

analoguereference would be an order of magnitude easier and cheaper.

analogReference(INTERNAL);

in setup if you have a Uno/Duemilanove

Or adjust the voltage divider circuit with the LDR in. You certainly don't need an opamp.

6

use the function map() in addition to analogReference

7

thanks....

The map function is not what i want. It maps only values, but don;t spread the it. The sensor doesn't get more sensitive in the area I want.

I gonna try the analogref functions, thanks for that!

But.....
i did some research on the web today and know now that a ldr is not the best device(sensor) to do this job. Temperature does react on the value.....
So this is a better option: tsl230r (IC wich read the light and send a frequency value to the arduino).

Hope that works better....

Marcel

8

IC wich read the light and send a frequency value to the arduino

Sparkfun.com has one...

$6