hi, i'm doing a little experience with infrared emission,reception modulation etc
eventough my system(very primitive) works fine indoor it is not the same outdoor,it looks that the sfh250 Ir receiving diode when exposed to the weak winter sun of northern Italy is able to generate about
-400 mV on a 1MOhm load
What is it due to? and how can i avoid it if possible?Shielding?Red glass filtering or what ??Thank you
Diego Italy
Photodiodes produce current. Resistors create voltage drop proportional to current. The usual remedies:
1) reduce load resistance, which also reduces sensitivity, of course 2) apply reverse bias voltage, which may require capacitive coupling if the amplifier circuit is sensitive to DC level 3) use a transconductance amplifier, which can be configured to keep voltage across the photodiode near zero voltsPaul Mathews
modulation
weak
glass
thank you,very much,at first
in the past days i used a TSOP1736,integrating filters ,demodulation and so on
his feature should be high immunity to environmental light,but while exposed to the sun passing fast the hand and shadowing it quickly seems enough to turn it's output active
strange,not?
>
Integrated IR photodetectors such as TSOP1736 usually include an optical filter that reduces effects of ambient light. However, they are not really designed to operate in daylight, since most people don't watch TV in daylight. Typically, their field of view is reduced by some type of aperture or tube placed in front of the photodetector. IR remote controls emit intense beams, and the 'commands' are repeated, with the user re-aiming the remote, until the desired results are achieved. You can use and aperture, tube, or lens to narrow the field of view. Paul Mathews
Use two photodiodes. Aim one at your source, the other someplace else neutral. Use a differential input and subtract one from the other.
Al
same
so
exposed
What will also work, and be simpler, is to wire the two photodiodes together, in parallel but with opposite polarity. (cathode of one to the anode of the other, and vice versa).
That way, the two should act as a single differential current source, requiring just a single amplifier or current-to-voltage converter.
My coworkers and I used such a configuration years ago for a laser spectroscopy measurement.
Mark
the same
to the
possible?Shielding?Red
course
coupling
keep
,demodulation and so
exposed
enough to
the fact is that the receiving circuit is mounted on a vehicle in a race track so i think that is difficult to separate useful signals from the "light floor"
i'm not shure it will work in my case but it looks interesting
Every time lot of things hint and ideas from the NG,thank you sincerely
Can you use a smaller load resistor? To avoid saturating the photodiode, the voltage should not be higher than about 250 mV or so.
Mark
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