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PICList Thread
'IR barrier and sunlight'
1998\11\11@161902 by Leonardo De Palo

flavicon
face
Hi PICer,

I have the necessity to count object, using a 16F84.

My idea is to use a couple of infrared diode and receiver (like the IR used
on TV).

But, thinking at the environment of the installation site, it possible that
some sunlight can arrive to the sensor, and I suppose that sunlight can
saturate the receiver photodiode.

I have the idea to try to minimize the effect of the undesidered light with
some black plastic tube, but before to begin to build the prototipe, I would
like know if exist a method to drive the LED to ignore o reduce the sunlight
saturation effect.

Anyone have some idea??

Ciao

Leonardo

1998\11\11@235330 by Tjaart van der Walt

flavicon
face
Leonardo De Palo wrote:
>
> Hi PICer,
>
> I have the necessity to count object, using a 16F84.
>
> My idea is to use a couple of infrared diode and receiver (like the IR used
> on TV).
>
> But, thinking at the environment of the installation site, it possible that
> some sunlight can arrive to the sensor, and I suppose that sunlight can
> saturate the receiver photodiode.
>
> I have the idea to try to minimize the effect of the undesidered light with
> some black plastic tube, but before to begin to build the prototipe, I would
> like know if exist a method to drive the LED to ignore o reduce the sunlight
> saturation effect.
>
> Anyone have some idea??
>

Use two diodes. Point one at the LED, and the other away from the LED.
Use an opamp to get the difference between the two signals.

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1998\11\12@043115 by Tom Handley

picon face
  Leonardo, in addtion to a light shield such as a tube, you want to modulate
the IR beam. A simple way to do this is to pulse the beam at a given rate and
have the receiver look for missing pulses. We use to use 555 timers for this
before microcomputers, in saw mills and other environments. You can also get
IR filters that are nearly opaque to ambient light. We used all three.

At 03:33 PM 11/11/98 +0100, Leonardo De Palo wrote:
{Quote hidden}

1998\11\12@083802 by Mike Keitz

picon face
On Wed, 11 Nov 1998 15:33:03 +0100 Leonardo De Palo
<leo.depalospamKILLspamPOMETIA.IT> writes:
>Hi PICer,
>
>I have the necessity to count object, using a 16F84.
>
>My idea is to use a couple of infrared diode and receiver (like the IR
>used
>on TV).

That;'s a good way to start.  The receivers are sensitive and have good
rejection of ambient light.  I don't know if these units like to receive
a continuous carrier, or if they have AGC that will try to cancel it out.
You may have to chop the transmitter on and off at a KHz or so in
addition to the 40 KHz carrier.


>
>But, thinking at the environment of the installation site, it possible
>that
>some sunlight can arrive to the sensor, and I suppose that sunlight
>can
>saturate the receiver photodiode.

Yes it can.  You can tolerate some sunlight, but it will be very
difficult to make it work if the sun shines directly into the receiver.

>
>I have the idea to try to minimize the effect of the undesidered light
>with
>some black plastic tube, but before to begin to build the prototipe, I
>would
>like know if exist a method to drive the LED to ignore o reduce the
>sunlight
>saturation effect.

It is important to exclude strong light that can saturate the receiver.
Lenses also work and have the advantage of collecting more light from the
desired direction.  But the key is to use modulation so that the receiver
can tell if the light being received came from the transmitter or
soemwhere else.  An additional advantage can be gained in a stationary
installation like this by synchronizing the transmitter and receiver.
The receiver has a balanced demodulator driven by a copy of the
transmitter's carrier.  In some circles this is called a "lock-in
amplifier".  An old-timey  567 tone decoder chip can implement the entire
system except for the LED driver and maybe the receiver preamp (though
the 567 input is decently sensitive as it is).


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1998\11\12@090259 by aya Baptista
flavicon
face
Hi Tom.
I think that is not the problem.
What Leonardo says is that the light may SATURATE the IR receiver. That
means the receiver will always be in ON state. Modulating the signal won't
do any better because the receiver is already receiving IR.

Regards,
AndrŽ Malafaya Baptista


{Original Message removed}

1998\11\12@100104 by Brian Striggow

flavicon
face
On Wed, 11 Nov 1998, Leonardo De Palo wrote:

>
> I have the idea to try to minimize the effect of the undesidered light with
> some black plastic tube, but before to begin to build the prototipe, I would
> like know if exist a method to drive the LED to ignore o reduce the sunlight
> saturation effect.
>

Here's two ideas.

a. some commercial photocells pairs use a modulated (high audio) transmitted
beam and active filters on the receiver to drag the transmitted signal (or
its absence) out of the noise.  We use these in the wood industry to detect
the presence of wood veneers; we have to turn down their sensitivity to
prevent 'seeing' thru the wood.  If your receiver doesn't completely
saturate, this might help you.  Of course this would require a few
analog components, which is anathema to a true pic'er.

b. The unexposed DEVELOPED roll ends of Kodak Ektachrome slide film makes a
passable IR pass filter.  Looks opaque to us, but passes a good bit of IR.
Talk nice to the people at the photo shop and they'll give you all you can
use.  Make sure you get slide film though, the exposed developed ends
of negative film looks the same but is opaque to IR.

1998\11\12@103401 by Tom Handley

picon face
  AndrŽ, the reason to modulate the IR beam is to prevent the effect of
saturation. You can normally detect the modulation even under direct sun
light. While you can do some fancy analog techniques to overcome the
problem, a simple missing pulse detector will do the job. Given a saturated
receiver, you can still amplify the signal and detect the missing pulse. I
use to design IR limit switches for use in very harsh environments back in
the 70's. We also added a simple light shield (ie: tube), a low-cost IR
filter, and lenses. We used a 555 timer for the transmitter and a 741
opamp used as a preamp, followed by a 555 timer to detect missing pulses.
We tested the system out to several hundred feet with direct sunlight
focused into the receiver.

  - Tom

At 01:52 PM 11/12/98 -0000, AndrŽ  Malafaya Baptista wrote:
>Hi Tom.
>I think that is not the problem.
>What Leonardo says is that the light may SATURATE the IR receiver. That
>means the receiver will always be in ON state. Modulating the signal won't
>do any better because the receiver is already receiving IR.
>
>Regards,
>AndrŽ Malafaya Baptista
>
>
>{Original Message removed}

1998\11\12@113331 by aya Baptista

flavicon
face
Hi Tom.
You mean it is possible to detect some millivolts at the output of the
receiver caused by the modulation of the IR LED? Wouldn't you detect noise
fluctuations too thinking it would be a pulse?

AndrŽ Malafaya Baptista


{Original Message removed}

1998\11\12@120856 by Andy Kunz

flavicon
face
At 07:32 AM 11/12/98 -0800, you wrote:
>   AndrŽ, the reason to modulate the IR beam is to prevent the effect of
>saturation. You can normally detect the modulation even under direct sun
>light. While you can do some fancy analog techniques to overcome the
>problem, a simple missing pulse detector will do the job. Given a saturated
>receiver, you can still amplify the signal and detect the missing pulse. I
>use to design IR limit switches for use in very harsh environments back in
>the 70's. We also added a simple light shield (ie: tube), a low-cost IR
>filter, and lenses. We used a 555 timer for the transmitter and a 741
>opamp used as a preamp, followed by a 555 timer to detect missing pulses.
>We tested the system out to several hundred feet with direct sunlight
>focused into the receiver.

As a test, I once used an IR detector circuit (Sanyo I believe) in it's
barest form - detector, 10uF cap, power, and scope probe.

I illuminated the front of the detector with a laser pointer (CW output).
Lots of light!

Next, I blinked my remote control at it.

The remote control signal passeed correctly.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\11\12@130854 by Peter L. Peres

picon face
On Thu, 12 Nov 1998, Tjaart van der Walt wrote:

> Use two diodes. Point one at the LED, and the other away from the LED.
> Use an opamp to get the difference between the two signals.

Better, pulse the transmitter and use an AC amplifier for read-out. Unless
the sun goes nova soon there should be no problems (but don't allow the
phototransistor to be saturated with sunlight in any case).

Peter

1998\11\12@140221 by Engineering Department

flavicon
face
< Leonardo De Palo writes in part>

>I have the necessity to count object, using a 16F84.
>
>My idea is to use a couple of infrared diode and receiver (like the IR used
>on TV).
>
>But, thinking at the environment of the installation site, it possible that
>some sunlight can arrive to the sensor, and I suppose that sunlight can
>saturate the receiver photodiode.



I've had great luck modulating the IR.  Unless the sunlight swamps the IR
detector completely (recess it in a black tube -- or thread the tube -- and
align the detector in such a way that the sun does not shine directly in)
you can pick out the modulated signal.

My PIC strategy ('54) was to read the detector with the IR sender off, raise
the IR sender and look at the detector for a change.  I didn't even bother
with an A/D -- just adjusted the bias to the detector so IR sender off was 0
and IR sender on was 1.  Not pretty, but the design has counted billions of
air freshners in a dozen really hostile industrial environments.

BTW, I seem to recall that color negative film overexposed in some way made
a very good IR filter.  Think it was in Electronics Design, but won't bet on
it.

Cheers,

Win
Image Logic Corporation

1998\11\12@141256 by Dave VanHorn

flavicon
face
> As a test, I once used an IR detector circuit (Sanyo I believe) in it's
> barest form - detector, 10uF cap, power, and scope probe.
>
> I illuminated the front of the detector with a laser pointer (CW output).
> Lots of light!


Lots of light around 630nM, which is outside the passband of the IR
filter.
Sunlight is broad-spectrum, and has a fair amount in the right band to
get through the filter. Still, it's an excellent demo that the filter
does what it's designed to do.

1998\11\12@142545 by Engineering Department

flavicon
face
<Tjaart van der Walt suggests cancelling incident sunlight as follows>

> Use two diodes. Point one at the LED, and the other away from the LED.
> Use an opamp to get the difference between the two signals.


I've seen detectors completely swamp in direct sunlight -- no response at
all.  The only solution I know of is to shade the detector and make sure the
direct sunlight doesn't reflect off the sender.  Perhaps that was the
problem that Leonardo De Palo  was getting at.

The cheapest shade I've used was a piece of black plastic with the detector
stuffed in one end of a threaded hole.  The threads really seem to keep
incident IR from bouncing around and the depth of the hole will (obviously)
narrow the detectors field-of-view.

Cheers,

Win Wiencke
Image Logic Corporation

1998\11\12@144357 by Engineering Department

flavicon
face
>b. The unexposed DEVELOPED roll ends of Kodak Ektachrome slide film makes a
>passable IR pass filter.  Looks opaque to us, but passes a good bit of IR.
>Talk nice to the people at the photo shop and they'll give you all you can
>use.  Make sure you get slide film though, the exposed developed ends
>of negative film looks the same but is opaque to IR.


I knew I'd heard of this trick, I just couldn't remember what film.

Thanks for the tip!

Cheers,

Win Wiencke
Image Logic Corporation

1998\11\12@144400 by Engineering Department

flavicon
face
< Andy Kunz writes in part>

>As a test, I once used an IR detector circuit (Sanyo I believe) in it's
>barest form - detector, 10uF cap, power, and scope probe.

>I illuminated the front of the detector with a laser pointer (CW output).
>Lots of light!

>Next, I blinked my remote control at it.

>The remote control signal passeed correctly.

Um, isn't the laser putting out an intense but narrow spectrum that's not in
the IR range?

Just a thought,

Win

1998\11\12@152922 by Andy Kunz

flavicon
face
>does what it's designed to do.

That was my point.  The other is that, regardless of the wavelength, there
was still a lot of energy received by tthe ciruit.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\11\12@152927 by Andy Kunz

flavicon
face
At 04:30 PM 11/12/98 -0000, you wrote:
>Hi Tom.
>You mean it is possible to detect some millivolts at the output of the
>receiver caused by the modulation of the IR LED? Wouldn't you detect noise
>fluctuations too thinking it would be a pulse?

But the noise probably doesn't occur regularly with the same frequency at
which you are modulating the transmitter.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\11\12@153313 by Pepper, Gary

flavicon
face
A visible laser diode will have negligible impact on the receiver
performance of most commercial IR receiver modules, because they
contain an optical bandpass filter, which discriminates against
visible light and obviously pass IR.

The addition of an IR transmission filter to any home made IR receiver
(that doesn't have an integral IR filter) makes sense, because it will
greatly improve the signal-to-noise ratio (in the presence of strong
sunlight) of the receiver.  The use of an IR filter will allow
detection of the IR signal at further distances from the transmitter
than for the situation of using no filter at all.

If an IR receiver doesn't have an IR filter in it, you could easily
"saturate" the receiver, using a visible light source, so that the
receiver would be incapable of detecting an IR signal.  IR-sensitive
semiconductor photodetectors are generally very sensitive to visible
light.  Conversely, visible light-sensitive photodetectors are
generally somewhat sensitive to IR wavelengths.  Ever tried looking at
an IR LED with your camcorder, for instance?

Hope this helps!
Gary

1998\11\12@153738 by Dave VanHorn

flavicon
face
Andy Kunz wrote:
>
> >does what it's designed to do.
>
> That was my point.  The other is that, regardless of the wavelength, there
> was still a lot of energy received by tthe ciruit.


The laser pointer energy never made it to the detector. The filter is
optical, and in front of the detector (in many cases built right into
the case of the sensor element)

Had you illuminated it with energy in the filter's passband, then that
would have been relevant.
They work indoors, because there are not a lot of sources with
significant energy in that band, and even fewer that are modulated at a
rate that will get past the electronic filter.

1998\11\13@023333 by »yvind Standal

flavicon
face
part 0 2070 bytes
SFH 506-xx  (xx is for the modulation frequency) from siemens
or
TSOP 12xx, TSOP 11xx, TSOP17xx from TEMIC/VISHAY



regards

¯yvind Standal
Nortroll AS

Tlf:      +47 74085514
Faks:  +47 74085501
email:  .....ostandalKILLspamspam.....nortroll.no
web:   http://www.nortroll.com





----------
From:   AndrŽ  Malafaya Baptista[SMTP:EraseMEABaptistaspam_OUTspamTakeThisOuTSE.EFACEC.PT]
Sent:   12. november 1998 15:13
To:     PICLISTspamspam_OUTMITVMA.MIT.EDU
Subject:        Re: IR barrier and sunlight

Hi Tom.
I think that is not the problem.
What Leonardo says is that the light may SATURATE the IR receiver. That
means the receiver will always be in ON state. Modulating the signal won't
do any better because the receiver is already receiving IR.

Regards,
AndrŽ Malafaya Baptista


{Original Message removed}

1998\11\13@053136 by Peter L. Peres

picon face
On Thu, 12 Nov 1998, Engineering Department wrote:

> >b. The unexposed DEVELOPED roll ends of Kodak Ektachrome slide film makes a
> >passable IR pass filter.  Looks opaque to us, but passes a good bit of IR.
> >Talk nice to the people at the photo shop and they'll give you all you can
> >use.  Make sure you get slide film though, the exposed developed ends
> >of negative film looks the same but is opaque to IR.
>
>
> I knew I'd heard of this trick, I just couldn't remember what film.

Along the same lines, black thin (usual) PVC electrician's tape is even
more transparent for IR (so are most PVC plastics unless filled). A quick
fix is a piece of that tape over the sensor window. You can add layers at
will.

Peter

1998\11\13@075851 by Tom Handley

picon face
  AndrŽ, yes. Again, we also used a shield (tube) and an IR filter as well
as a lense. I forgot where we got the filters from but they were low-cost.
They looked like small, red, plastic disks. As far as noise, we rarely had
a problem. We did use a filter in some applications. We also designed
car wash controls for Hanna Industries and several other custom jobs. The
product was very reliable and low-cost.

  - Tom

At 04:30 PM 11/12/98 -0000, AndrŽ  Malafaya Baptista wrote:
>Hi Tom.
>You mean it is possible to detect some millivolts at the output of the
>receiver caused by the modulation of the IR LED? Wouldn't you detect noise
>fluctuations too thinking it would be a pulse?
>
>AndrŽ Malafaya Baptista
>
>
>{Original Message removed}

1998\11\16@022654 by leo.depalo

flavicon
face
Hi PICer friends,

many thanks for a lot of suggestion about the subject. In my mind now I have
a clear idea whay can I do.

I try to explain.

The application is very similar to a mail box (for paper mail), whit the
same hole to insert mail. (2 x 6 inch).

Each time a envelope in feeded trought the hole an IR barrier intercept it
and count.

As a principle of operation, I would like use only 16F84 resource, on one
pin I modulate the LED and charging a capacitor, and on other pin i read
trought a phototrasnistro the light until the capacitor is discharged.

Do you agree??

Ciao

Leonardo

1998\11\16@120216 by Engineering Department

flavicon
face
<Leonardo writes>

The application is very similar to a mail box (for paper mail), whit the
>same hole to insert mail. (2 x 6 inch).
>
>Each time a envelope in feeded trought the hole an IR barrier intercept it
>and count.
>
>As a principle of operation, I would like use only 16F84 resource, on one
>pin I modulate the LED and charging a capacitor, and on other pin i read
>trought a phototrasnistro the light until the capacitor is discharged.
>
>Do you agree??


Why is the capacitor used?  The '84 is perfectly able to time off a sampling
period.

Cheers,

Win

1998\11\17@020648 by leo.depalo

flavicon
face
<Cheers writes>

>Why is the capacitor used?  The '84 is perfectly able to time off a
sampling
>period.


I would insert the capacitor because my idea is:

set ON a pin to drive the IR LED and load the capacitor, then put OFF the
pins and read continuosly the light emitted by the IR LED powered by the
capacitor. When the level of IR drops, in a time windows predefined, iI know
thath the IR come from the LED and not from the environment.

Obviously if the IR don to light the receiver, I assume that a obiect stay
between the IR LED and the receiver.

(I hope to have exposed clearly my think, sorry but the englis is not my
motherlanguage)


Ciao

Leonardo

1998\11\17@032903 by Mark Willis

flavicon
face
leo.depalo@POMETIA.IT wrote:
{Quote hidden}

 So the capacitor's across the LED (in parallel)?  I wouldn't think
that's the best way to do this, you could do this with just a 555 (But
use a PIC!) - if you repeatedly turn the LED ON for a short while (then
read the IR results), turn the LED off for a short while (then read the
IR results), loop through that continuously - you'll see a larger
difference between the LED ON and the LED OFF readings, if no object;
and very little difference, if the object blocks the light.  You want a
decent path for the light between the transmitter & receiver.  (No
Italian here, just some high school Spanish, German, and Russian, years
ago.  Someone?  Probably someone who's done this on a PIC, which I
haven't, too.  <G>)  (I think we diode-ORed this once, or something.)

 Mark, @spam@mwillisKILLspamspamnwlink.com, "You'd be Surprised what you can make out of
2 paper grocery bags full of 7410 TTL IC's!"  {High School horror story.
<G>}

1998\11\17@155123 by Engineering Department

flavicon
face
<Win replied>
>>Why is the capacitor used?  The '84 is perfectly able to time off a
>>sampling period.

<Leonardo replies>
>
>I would insert the capacitor because my idea is:
>
>set ON a pin to drive the IR LED and load the capacitor, then put OFF the
>pins and read continuosly the light emitted by the IR LED powered by the
>capacitor. When the level of IR drops, in a time windows predefined, iI
know
>thath the IR come from the LED and not from the environment.

Can you use one PIC pin as output to control the LED and use another pin as
input connected to the IR detector?

When you pulse the LED you should detect a corresponding IR detector pulse.
You can even get send and receive complicated pulse patterns to be sure you
are detecting your IR and not some incident IR.

Here is a quick outline of the code loop -- it uses one register (counter)
for the sake of clarity:

           1) Load counter register
           2) Turn on LED
           3) Read detector
           4) Done when IR is detected -- goto 8
           5) Decrement counter register
           6) No IR found if counter register is zero -- goto object found
           7) Repeat -- goto 3
           8) Turn off LED
           9) If counter register was not decremented -- goto saturated IR
error handler
          10) Repeat whole test -- goto 1

You could eliminate a pretty big capacitor from your design and avoid timing
uncertainties caused by temperature and component variation.  Also, your PIC
will not need a timing routine.

>Obviously if the IR don to light the receiver, I assume that a obiect stay
>between the IR LED and the receiver.


Either that or there is some alignment problem.

>(I hope to have exposed clearly my think, sorry but the englis is not my
>motherlanguage)


It is not my mother language either...<g>

Cheers,

Win

1998\11\18@044144 by John Sanderson

flavicon
face
Bonjourno Leonardo & PIC.ers,

>>Why is the capacitor used?  The '84 is perfectly able to time off a
>>sampling
>>period.
>
>
>I would insert the capacitor because my idea is:
>
>.set ON a pin to drive the IR LED and load the capacitor, then put OFF the
>pins and read continuosly the light emitted by the IR LED powered by the
>capacitor. When the level of IR drops, in a time windows predefined, iI know
>thath the IR come from the LED and not from the environment.
>
>Obviously if the IR don to light the receiver, I assume that a obiect stay
>between the IR LED and the receiver.
>
>Ciao
>Leonardo
..
IR discrimination is very effective if you just:
..
Turn IRED ON,  read the state of the phototransistor & check that it
is ON, i.e. agrees with the state of the IRED.
If so, turn the IRED OFF & check for OFF at the sensor.
Arrange a software loop to do this, say 256 times consecutively.
In the event the IRED & sensor ever disagree, set a `fail' flag & drop out
of the loop.
If they always agree through the process, set a `succeed' flag.
..
This way you don't have to worry about loop timing, be aware that
phototransistors are a tad slow in turning on & off
-Tc= ~ 5uSec or so I think.
Your loop might need delays in it to allow the thing to settle at each transitio
n.

Best regards,   John
..
email from John Sanderson at
JS Controls, PO Box 1887, Boksburg 1460, Rep. South Africa
Manufacturer & purveyor of laboratory force testing apparatus
and related products and services.
Tel/fax: Johannesburg 893 4154    Cellphone 082 453 4815

1998\11\19@090235 by Tom Handley

picon face
  AndrŽ, yes. Again, we also used a shield (tube) and an IR filter as well
as a lense. I forgot where we got the filters from but they were low-cost.
They looked like small, red, plastic disks. As far as noise, we rarely had
a problem. We did use a filter in some applications. We also designed
car wash controls for Hanna Industries and several other custom jobs. The
product was very reliable and low-cost.

  - Tom

At 04:30 PM 11/12/98 -0000, AndrŽ  Malafaya Baptista wrote:
>Hi Tom.
>You mean it is possible to detect some millivolts at the output of the
>receiver caused by the modulation of the IR LED? Wouldn't you detect noise
>fluctuations too thinking it would be a pulse?
>
>AndrŽ Malafaya Baptista
>
>
>{Original Message removed}

1998\11\19@125527 by Peter L. Peres

picon face
On Thu, 12 Nov 1998, Engineering Department wrote:

> >b. The unexposed DEVELOPED roll ends of Kodak Ektachrome slide film makes a
> >passable IR pass filter.  Looks opaque to us, but passes a good bit of IR.
> >Talk nice to the people at the photo shop and they'll give you all you can
> >use.  Make sure you get slide film though, the exposed developed ends
> >of negative film looks the same but is opaque to IR.
>
>
> I knew I'd heard of this trick, I just couldn't remember what film.

Along the same lines, black thin (usual) PVC electrician's tape is even
more transparent for IR (so are most PVC plastics unless filled). A quick
fix is a piece of that tape over the sensor window. You can add layers at
will.

Peter

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