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Topic: compensating for light resistance in different photoresistors (Read 977 times) previous topic - next topic

esmi83

hello
I wonder if there is a way to compensate for the resistance in photoresistors with the pulldown resistor? For example if i use a GL5539(light resistance50-100KO dark resistance 5MO)  it gives me the spectre i want with a 68Kohm resistor for a pulldown resistor, But if i use the GL5549(light resistance 100-200KO) dark resistance 10MO the values are å bit too low, is there any way to compensate this with switching the pulldownresistor, and is there any formulas to do this?

jremington

#1
Jan 04, 2014, 06:58 pm Last Edit: Jan 04, 2014, 07:26 pm by jremington Reason: 1
If you had already gone through any of the many tutorials on using photoresistors, you would know the relevant equation. What, exactly, do you want to measure and why do you want to use different photoresistors?

Magician

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is there any way to compensate this with switching the pulldownresistor, and is there any formulas to do this?

Of course, you can wire a few resistors that differs in values, for example, 1k, 10k, 100k, 1M etc, than you connect them together at one end - to LDR,  and connect to different digital pins at the other end. Switching pinMode from input to output and setting it LOW you can select appropriate resistor by software.  The highest sensitivity level is when R equals to LDR, or when avalogRead close to V/2. You may write an algorithm to switch pulldown resistor automatically (auto-ranging) .

esmi83

thanks, i do not need to use different photoresistors, but i hawe alot of different ones and i am going to build several sensors that should give the same results at the same light, thanks

Grumpy_Mike

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i am going to build several sensors that should give the same results at the same light,

You will be lucky to do that. There are all sorts of variations that will stop that from happening. You might get it right for one light level but I doubt that they will track over changing levels.

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