Need circuit idea for light sensor.

[Ignas Pranckevi]

Hello I need advice for my solar tracker system. I'm trying to create light sensor using LM358 OA and LED sensor diode. I use controller measurement light signal. I use controller Atmega32 which I connected with OA output (with ADC port). I protect it from high voltage signal with SD. So I want to get a range between 0 - 3.3 V from light sensor. My solar signal must to depend from light intensity of days. I add my project circuit above but it's not correct. Actually I don't know what is wrong with my circuit because I'm getting 0.7 V signal when is dusk and 0.7 when is dark. So it's not tolerated for this. Of Course I get correct signal if light intensity is much stronger signal that dusk or dark.
https://obrazki.elektroda.pl/9822506800_1430645844.png

 

[FvM]

Not sure which sensor you are actually using, 02BZ2.2 is a zener diode. Presumed it's any kind of photodiode (or a LED used as photo diode), you can expect better results when operating the diode in zero voltage bias than in photo element mode. See the below circuit as an example.

 

[KlausST]

Hi,

Yes, FvM is amplifying current, while your circuit is amplifying voltage.

For photodiodes the current is about proportional to light density, the voltage is far from being proportional.
Voltage -with no load - is soon at a specific level and changes not that much after that...

LEDs may be used as light sensor, but why not using a standard photodiode? The output signal is much higher and predictable/calculable.

Klaus

 

[Ignas Pranckevi]

Hello. Actually I used a simple LED diode, after I used photodiode and I compared a both. Now I'm using photodiode. Yes you are right for zener diode there was really zener diode. I have a several issue, why do you use in this example OPA353? Perhaps its debends something from it? What's nominal of capacitor?

 

[FvM]

As said it's just an example circuit. You can use LM358 as well. Don't necessarily need a capacitor with slow OPs. The resistor has to be adjusted to the application, so that you get full scale output at maximum irradiance.

 

[Ignas Pranckevi]

Hi Klaus. Originally I tried with LED and I saw that wasn't a good result which I want to get. After I tried with a photodiode, of course the result is was far batter comparing with LED. At now I'm working with photodiode but result is not accurate for dusk and dark.

 

[Ignas Pranckevi]

Hi FvM. I tried your example, I think it works but this is very sensitive. Parhaps you can advice me for sensitive, how to reduce it?
I put on several capacitor 68 nF between OA Output and Negative but nothing changes for it.

 

[KlausST]

Hi,

read post5:

The resistor has to be adjusted to the application, so that you get full scale output at maximum irradiance.

Klaus