Sensor choice for solar tracker

[ojal]

Hello,

As part of various solar projects, I want to make a sensor that allows me to capture the position of the sun.

I read several discussions right here and the recommended solution seems to be the use of LEDs, a lot of documentation on the REDROCK site: http://bit.ly/kXIkPc

I wonder why not just use photoresistors? These are electronic components made so that their resistance varies with the light intensity while the use of LEDs is a 'biased' use of LEDs ...

Would LEDs have a particular advantage?

Thank you in advance for your answers ;-)

[dedeleco]

The two, with also photodiodes and photostransistors to add to the list, that is to say the four work with different assemblies, but the small inexpensive LEDs have already incorporated a lens which makes them more directive, lens which must be added to the photoresistor ( or with a long tube in front).
Nearly any semiconductor makes a light detector, diode or transistor with a case open to the sun.

We can even measure by the heating of an insulated surface in the sun under a lens, parabola or at the bottom of a long tube with the voltage on a cheap diode, voltage which varies with temperature, and therefore any diode or transistor makes a temperature sensor which captures the heat linked to sunlight !!

The prices differ quite strongly especially for the endangered models in some old montages !!

[ojal]

I imagine that if photodiodes were designed, it is that they must bring something more than the simple diodes right?

I put a voltmeter on a led in the sun and it is impressive in any case in tension ...

[dedeleco]

I put a voltmeter on a led in the sun and it is impressive in any case in tension ...

the sun is impressive in energy 1KW / m2 and therefore the small LED diode with its lens which concentrates receives 100mW / cm2 and therefore on its surface of 5mm in diameter approaches with 20mW of its maximum power !!

With a small magnifying glass the sun burns very strong!
We thus measure well all the solar energy wasted on our roofs in summer which could heat us in winter for free and in perpetuity without dangerous nuclear !!
http://www.dlsc.ca/DLSC_Brochure_f.pdf

I imagine that if photodiodes were designed, it is that they must bring something more than the simple diodes right?

Obviously, according to the needs, an ordinary diode has a box which cuts the light and therefore it is necessary at least a box with window.
A transistor with cut out box becomes a good photo-transistor !!
In addition these diodes detect more infrared than visible and therefore we have developed various diodes and phototransistors with different sensitivities and even LEDs which make visible light in opposite direction with a current and not only infrared.
There are very expensive ones for precise measurements.

To detect the orientation of the sun the cheap LED is enough. She risks dying even from too much sun.

[ojal]

So I'm going to go on these little leds ...

I will still try to characterize some LEDs based mainly on their angle with the light rays ...
@ to follow...

[dedeleco]

Very well, we can add a small plastic lens to them, if necessary, or even have two in parallel, a little directive and another very directive.

[ojal]

I come back to you because I am not progressing in my research ...
As already indicated, when I measure the voltage across an LED, I can see the voltage increase until reaching a certain threshold depending on each model of LED.
This voltage is around 1,5V.

The problem is that I cannot measure this voltage through the analog / digital converter which is on the plate which I use which in this case is an ARDUINO ...

On a forum ARDUINO, I was told that I could not measure this voltage because the LED does not really produce a voltage, but only a very low intensity ...

Do you understand why I can measure the voltage with the voltmeter when I cannot record it through my A / D converter ... ??

Thank you in advance for your contributions ;-)

[Forhorse]

Try it out already with a follower op-amp, possibly with a slight gain

[ojal]

Try it out already with a follower op-amp, possibly with a slight gain

Hello Forhorse,

I'm reaching my limits in electronics ... I'm going to rewrap the PDO, I only have an LM741 on hand ...
You could explain to me in a few lines the problem that I meet and advise me on a montage?

Thank you ;-)

[dedeleco]

Which ARDUINO among those:
http://fr.wikipedia.org/wiki/Arduino
http://arduino.cc/en/Main/Hardware

What are the impedances of the inputs of the converters ,,,

A voltmeter is about 1 megaohm and you have to know for the converter which can be 1 to 10KOhm if it is rudimentary ????.
Read the instructions of the ARDUINO and its microprocessor !!!

Read page 195: 10KOhms advised or slow down to lengthen the conversion time !!
http://www.atmel.com/dyn/resources/prod ... oc2486.pdf
Try with a low impedance voltage of 10KOhms coming from a battery then with a very bright LED which gives a good current ...
or the op amp ... (LM 324 or LF 356 easier than 741), see the National Semiconducteur application notes)