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Old 14th December 2005, 10:15 PM   #1
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Default Fototransistor

Hi,

Im looking for a fototransistor for ambient light. I've found one type RPM-075PTT86 at digi-key, but it's a bit beyond my soldering skills. There are plenty of fototransistors that are tuned to the ir range so I'm wondering if those will work. If not, will adding a ir absorbant filter do the trick?

Llafriel
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Old 8th January 2006, 10:42 PM   #2
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You are better off using a CDS photocell for ambient light aplications.
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Old 10th January 2006, 03:09 PM   #3
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Silicon photo transistors have peak sensitivity to the near infra red and can hardly see blue light. The (black) package is designed to block visible light so adding an infrar red blocking filter will end up with nothing.

If you just want to experiment, carefully cut the top off a TO-18 transistor eg bc108.
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Old 10th January 2006, 03:22 PM   #4
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Maybe this one?
http://www.elfa.se/elfa-bin/setpage....ok=2021364.htm

(Sorry it is in swedish, but that should be OK for the threadstarter, I hope.)
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Old 10th January 2006, 03:45 PM   #5
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Thanks for the replies guys. The elfa kind is a good example of what I'm thinking about. It responds to visible light but peaks in the ir range. Will I be able to measure ambient light with this, ranging from darkness to daylight?
I'll probably use a photocell though, but what are their response above 100 lux? Daylight in a room is more than 100 lux isn't it?
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Old 10th January 2006, 08:19 PM   #6
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A plain photo transistor will work in daylight. The only light source which have not much IR is "lysrör" tube??? lamps.

If you want a sensitive transistor it must be a with the base connected. You must also connect the transistor in class A in order to increase the light gain.

I work commercially with designing photocell equipment so I know some. If you want to do some experimenting I have my drawers full of photo transistors. I will check what I have.
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Old 10th January 2006, 08:30 PM   #7
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Quote:
Originally posted by Christer
Maybe this one?
http://www.elfa.se/elfa-bin/dyndok.p...ok=2021364.htm

(Sorry it is in swedish, but that should be OK for the threadstarter, I hope.)
this is in english ( lang=en )
http://www.elfa.se/elfa-bin/dyndok.p...ok=2021364.htm
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Old 10th January 2006, 09:31 PM   #8
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What I'm looking for is most likely very simlple. I want to a lamp to compensate for varying light. Dim when dark and brighter according to ambient light. Be it roomlighting and/or daylight. Not just two levels but varying intensity following ambient light.
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Old 11th January 2006, 12:49 AM   #9
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A CDS photcell is definitley the simplest way to go. Try the Clairex or EG&G Vactec websites. There are application notes there. You can also try searching the links at www.epanorama.net . Lots of good stuff there.
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