Direct sunlight sensor

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I want to make something to detect whether there's direct sunlight  
shining on particular place. I thought the obvious approach would be to  
use a pair of light dependent resistors (LDR) - one located where it  
will definitely be in direct sunlight (when the sun is shining) and  
another that is at the location to be tested. Compare the resistances,  
and the result should be clear enough.

But this means that at least one LDR will be in direct sunlight for  
extended periods, and I can find nothing in the datasheets to indicate  
whether the devices will survive that. My concern is UV degradation of  
the encapsulation material.

I can put them behind glass, which will provide some protection, but  
even then, they'll have to survive some UV.

Anyone have experience of this?

Sylvia.

Re: Direct sunlight sensor
On 29/10/2015 4:41 PM, Sylvia Else wrote:
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UV camera lens filters? Expensive at up to $20 a pop each for new ones.
Cut up a pair of polarising sunglasses? Maybe free if you already have  
an old pair.
PH

Re: Direct sunlight sensor
Adding sci.electronics.design, which got left out by mistake.

On 29/10/2015 5:41 PM, Sylvia Else wrote:

 > I want to make something to detect whether there's direct sunlight
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Re: Direct sunlight sensor
On 10/29/2015 09:25 AM, Sylvia Else wrote:
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Perhaps you can use a small solar cell as the transducer? These should  
survive direct sunlight during some decades.

Some time ago we even purchased a calibrated one, which could be used  
for absolute measurements. I had a quick look but was unable to dig up  
more details on it...

Pere

Re: Direct sunlight sensor
On 10/29/2015 4:25 AM, Sylvia Else wrote:
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Use a photodiode.  Cheaper, better, more reliable, multiple sources.  
For direct sunlight, something like an Everlight PD204-6C (19 cents in  
qty 10) would work fine.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Direct sunlight sensor
On Thu, 29 Oct 2015 19:25:59 +1100, Sylvia Else

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Are you attempting to discriminate between "direct sunlight" and
diffues sunlight i.e. some cloud obscuration?  If so I suspect the
LDR's may disappoint you.

Re: Direct sunlight sensor
On 30/10/2015 2:19 PM, pedro wrote:
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More between direct sunlight, and shadowed.

The project is to control a pivot-arm awning so that it extends only as  
far as is required to prevent direct sunlight entering a window. The  
window is almost exactly west facing, so the required extension varies  
from none at all during half the day, to fully extended towards sunset.

I'm intending to put one sensor just below the window. The awning will  
then extend until the sensor is in shadow, plus a bit. As the sun  
moves[*] across the sky, the sensor will again be exposed, at which time  
the awning will be extended further.

Eventually the other sensor will indicate that there's no longer any  
direct sunlight anyway, and the awning will be retracted.

Sylvia.

[*] Anyone wanting to point out that it's really the Earth that moves  
will be ignored.

Re: Direct sunlight sensor
On Fri, 30 Oct 2015 17:30:16 +1100, Sylvia Else

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[snip]

Interesting idea.  My home office windows face west and the HOA rules
prohibit awnings.  But I have interior (louvered) shutters that would
benefit from such an automatic control.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: Direct sunlight sensor
On 31/10/2015 2:10 AM, Jim Thompson wrote:
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For a fixed installation like this, you dont really need a sensor at  
all.  The suns location is completely calculable, all you need is the  
date/time and location.

Get the time from a local clock or net server, set the location, and you  
can do the geometry from the sun azimuth and altitude to get the angles  
for control.

Re: Direct sunlight sensor
wrote:

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I abhor microprocessors... the world is ANALOG O>:-}

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I like stand-alone systems.  I'm the one responsible for the
"limp-home" ignition system in GM products.  Those dumb-asses
initially wanted your car to drop dead if the timing failed and your
car's emissions went up.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: Direct sunlight sensor
On 31/10/2015 11:48 AM, Jim Thompson wrote:

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I confess that my planned implementation includes a PIC. There are some  
issues to be dealt with - people walking in front of the sensor,  
intermittent sunlight due to clouds, and the rapid changes that occur as  
the sun intersects the extended plane of the wall. No doubt these could  
all be handled using analogue circuitry, but using a PIC will make life  
simpler - particularly as I have much more experience with software than  
I do electronics.

Sylvia.

Re: Direct sunlight sensor
On 10/30/2015 8:56 PM, Sylvia Else wrote:
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The sensor only needs to have a very slow response anyway, so why would  
it respond to people walking in front of it?  When clouds are in the way  
both sensors will be shaded, so it shouldn't cause any problems.  I'm  
not sure what you mean be the sun intersecting the extended plane of the  
wall.  Do you mean self shading because the sun is blocked by the building?

--  

Rick

Re: Direct sunlight sensor
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 maybe use something slower than LDRs,  eg: thermistors.
  
--  
  \_(?)_

Re: Direct sunlight sensor
On 31/10/2015 6:08 PM, rickman wrote:
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The sensor needs to be quick so that the awning extension will stop as  
soon as the window is fully in shadow (plus a bit to prevent excessively  
frequent movement).

As for the extended plane thing, just after the sun has moved to a  
position where a wall is first illuminated, the shadows move very  
quickly. I think the awning needs to be extended some distance  
regardless of the sensor, again to avoid excessively frequent movement.

Sylvia.

Re: Direct sunlight sensor



...
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I was wondering if you would have any control of the speed that the awning  
moves, so I was looking at the sorts of things available. I notice that you  
are re-inventing the wheel, because sun sensors (and wind sensors too) for  
controlling awning motors are commercially available.

It would not surprise me if such sensors were expensive, or perhaps you just  
relish the challenge of making your own. However, perhaps you could get some  
ideas from a sensor made for the job?





Re: Direct sunlight sensor
On 1/11/2015 6:32 AM, Andy Wood wrote:
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Such examples as I've found just extend the awning to its end stop when  
the sun is detected, and completely retract it when it's not. I want  
something smarter than that.

Sylvia.

Re: Direct sunlight sensor
On 10/31/2015 7:34 AM, Sylvia Else wrote:
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You make it sound like the extension will be deployed from fully  
retracted to some significant extension.  If that is done, then yes,  
fast reaction is needed, but once it finds it's position, it can operate  
with a much slower response time.


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I'm still not picturing this, but that's ok.

--  

Rick

Re: Direct sunlight sensor
On 1/11/2015 7:15 PM, rickman wrote:
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It's not a one off. As the sun moves across the sky, the sensor will  
again be exposed and the awning further extended.

Sylvia.

Re: Direct sunlight sensor
On 11/1/2015 3:26 AM, Sylvia Else wrote:
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I'm not clear what you are saying.  Of course it will have to adjust  
multiple times during the day.  But the movement does not need to be  
anything remotely fast, so the sensor does not need to be quick  
responding.  Even if the awning has a little overshoot, that just means  
it will be a little while longer before it adjusts again.  Any control  
system will have overshoot and a lag in response.  The only issue is how  
much is acceptable and how much is too much.

I can't imagine the shadow of a passing bird or a person walking by  
would have to upset a device like this that is tracking the movement of  
the sun.

--  

Rick

Re: Direct sunlight sensor

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Why does it have to track the sun?  Put the sensor at the bottom of
the window.  If it's in the sun, extend the awning until it isn't.

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