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IR diode looks photovoltaic outdoor

B

blisca

Jan 1, 1970
0
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
 
P

Paul Mathews

Jan 1, 1970
0
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 volts

Paul Mathews
 
B

blisca

Jan 1, 1970
0
Paul Mathews said:
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 volts

Paul Mathews



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?
 
P

Paul Mathews

Jan 1, 1970
0
[email protected]...









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?



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- Show quoted text -- Hide quoted text -

- Show quoted text -

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
 
A

Al

Jan 1, 1970
0
Paul Mathews said:
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
 
R

redbelly

Jan 1, 1970
0
Use two photodiodes. Aim one at your source, the other someplace else
neutral. Use a differential input and subtract one from the other.

Al

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
 
B

blisca

Jan 1, 1970
0
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"
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).

i'm not shure it will work in my case but it looks interesting
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
Every time lot of things hint and ideas from the NG,thank you sincerely
 
R

redbelly

Jan 1, 1970
0
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

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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