Direct sunlight sensor

[Sylvia Else]

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.

 

[Peter Howard]

On 29/10/2015 4:41 PM, Sylvia Else wrote:

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.

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

 

[Clocky]

On 29/10/2015 2:41 PM, Sylvia Else wrote:

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.

Automotive auto-lights on features often rely on a light sensor on the
dash which incorporates a UV filter.

They may be LDR's or photodiodes, but either should work.

 

[Sylvia Else]

On 30/10/2015 2:19 PM, pedro wrote:

On Thu, 29 Oct 2015 19:25:59 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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
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.

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.

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.

 

[Andy Wood]

"Sylvia Else" wrote in message news:d9dtdpF62coU1@mid.individual.net...

I want to make something to detect whether there's direct sunlight shining
on particular place...

I once inadvertently made a sunlight detector. I needed a simple
photo-switch to turn on some LEDs when it got dark, and I made one from
parts in my junk box - an LDR and a LM3900. I had the LDR connected between
the positive supply and one of the LM3900 inputs, and I figured that I did
not need any additional series resistance.

Although the original was used successfully indoors for years I was wrong! I
later made another one, which I mounted on an outside wall. This worked for
a few months, but then failed, when with the change of seasons, the LDR got
exposed to direct sunlight. The resistance of the LDR went so low that the
current into the LM3900 input was enough to destroy it.

Due to the one-time nature of this detection, I won't recommend it.

 

[Jim Thompson]

On Thu, 29 Oct 2015 17:41:59 +1100, Sylvia Else
<sylvia@not.at.this.address> wrote:

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.

Maybe something like this...

<http://www.analog-innovations.com/SED/AwningController.pdf>

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Joe Hey]

On Fri, 06 Nov 2015 17:43:45 -0700
Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Thu, 29 Oct 2015 17:41:59 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Maybe something like this...

http://www.analog-innovations.com/SED/AwningController.pdf

...Jim Thompson

I think you don't need to worry too much about saturation.
In 'really bright sunlight' the shaded photo diodes will be far from
saturated and all your equations will still hold.

In case
1: I1 >> I2, I1 >> I3
2: I1 >> I2, I1 ~ I3
3: I1 ~ I2, I1 ~ I3

I like it.

joe