solar tracker-difference btw 2 photo sensors

[wutan1]

Hi
I am looking for a very simple solution to measure if the difference voltage of 2 photo diodes is within a certain range. If both sensors see approx the same light, solar tracker should switch off to save battery.
Cant use a window comparator, as I need to be able to adjust voltage range the tracker should switch off.
Could subtract the voltages, then precision rectify....but thats too complicated.
Any simple solution with 1 or 2 op amps or comparators out there?
Thanks!
wutan

 

[jami007]

here is the simplest solution

https://www.edaboard.com/threads/239792/

 

[jiripolivka]

What happens to your solar tracker if clouds cover the sky?!

 

[jami007]

it will stay where it is, because untill its sensors recieve equal light the output remains zero whether its day or night

---------- Post added at 10:40 ---------- Previous post was at 10:38 ----------

also the LDRs are very sensitive to light so in a cloudy day it will folow the higher source of light and keep pointing towards the light source

 

[jiripolivka]

I always wonder why many people build "solar trackers" with electronics which fails by any cloud... While, since ~1750, astronomers pointed their telescopes to any visible star (including the Sun) by using the polar axis and a simple clock drive....?!

 

[betwixt]

Jiripolvka, the only reason I can think of is a situation where the solar tracker may be portable and it should start tracking whatever position it is placed. If that is the case, it would need azimuth as well as lateral control to work properly. I have argued elsewhere on EdaBoard that a simple slow motor, or stepper motor is a better solution for exactly the reason you point out. All it then needs is a timer to return it to sunrise direction overnight.

Brian.

 

[jiripolivka]

Jiripolvka, the only reason I can think of is a situation where the solar tracker may be portable and it should start tracking whatever position it is placed. If that is the case, it would need azimuth as well as lateral control to work properly. I have argued elsewhere on EdaBoard that a simple slow motor, or stepper motor is a better solution for exactly the reason you point out. All it then needs is a timer to return it to sunrise direction overnight.

Brian.

Yes, Thank you, Brian! I think this is the only correct way to go. You can also add a programmed "latitude" drive, to correct the N/S pointing as it varies over the year. Light sensors are nice but fail with any cloud cover.
To get the precision polar axis pointing, for < $200 several small telescopes are sold (by Meade , Celestron, etc.) with an electronic pointing drive allowing to get the polar axis fast and anywhere. You can carry it and use to adjust any system in a position, then take it away. Or you can ask an astronomer for such service; many do it every clear night.

 

[betwixt]

It's exactly what I do with my Celestron - on those rare clear nights!

Brian.