outdoor light sensor - seal the box? or not?

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gskinner
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Location: broomfield CO 80020
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Posted by gskinner: Wed. Oct 22, 2008 - 04:34 AM
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I have made a few versions of a sensor that is mounted outside to measure sunlight.
http://www.elec-solutions.com/pr...
It has an atmel processor inside talking over cat5 wire to another atmel processor inside the building.
The board outside is conformal coated (except for the sensor itself) we used glass so it would not discolor over time.
The early versions had trouble with leaks, so we kept making better seals. At this point it does not leak, but it does suffer from condensation if it was cold and damp then changes to sunny.

so the question is - do I put a hole in the bottom of the box to let the parts breathe?
other solutions?

thanks in advance

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Learning and Information, General Electronics
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js
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Location: Sydney, Australia (Gum trees, Koalas and Kangaroos, No Edelweiss)
Posted by js: Wed. Oct 22, 2008 - 05:29 AM
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Quote:
do I put a hole in the bottom of the box
That would be one thing I was going to suggest. Not sure however how much error you would get in the ambient light reading with condensation on the lens.

Can you use a 5W resistor inside as a little heater? You would then need to adjust the temp I guess, but if the station needs to work in below 0 ambient it may be necessary.

As a matter of interest which sensor did you use? Some of them are very sophisticated going up to some 40,000 lux.

Does the sensor also read temperature with a Stevenson shield?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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gskinner
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Location: broomfield CO 80020
Posted by gskinner: Wed. Oct 22, 2008 - 07:33 AM
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I started with the TAOS (used to be TI) sensors - TSL2561. worked OK, but the mega88 occasionally lost the I2C signal, and then we discovered the unit did not work well in the cold.
So we changed to the osram SFH5711. It can handle direct sunlight and works at pretty wide temperatures. not as "accurate" but for this application it is sufficient.
we are not actually measuring temperature with this part, just sunlight and wind.
I would expect if we ever need to measure temperature, the sensor would not want to be on the roof.

what is a Stevenson shield?

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js
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Location: Sydney, Australia (Gum trees, Koalas and Kangaroos, No Edelweiss)
Posted by js: Wed. Oct 22, 2008 - 08:26 AM
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Quote:
what is a Stevenson shield?
Should have been screen not shield... :?
http://en.wikipedia.org/wiki/Ste...

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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