Searching \ for '[EE]: Light Sensors' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/io/sensors.htm?key=sensor
Search entire site for: 'Light Sensors'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: Light Sensors'
2001\11\14@153849 by Peter Grey

picon face
I wish to measure light during the night. I am told that typical levels are
around 0.1 lux. They want a wide range with good resolution. By the way it
must be light and cheap! Has anyone got any suggestions? I am trying to
measure a broad band of visible light that animals are exposed to. The moon
is also a factor.

TIA


Peter

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2001\11\14@155745 by Douglas Butler

flavicon
face
You can start with the short circuit current of a solar cell.  It will
be cheap and sensitive.  You may need a logarithmic amp before you
digitize.  Accurate log amps are not cheap.  How accurate do you need to
be?

Sherpa Doug

> {Original Message removed}

2001\11\14@163515 by Peter Grey

picon face
At 15:53 14/11/01 -0500, you wrote:

I am sorry but the light reading should have been 0.01 Lux. I am just now
trying to determine the full range and accuracy required. I will forward
this when known.

Thanks,

Peter
>You can start with the short circuit current of a solar cell.  It will
>be cheap and sensitive.  You may need a logarithmic amp before you
>digitize.  Accurate log amps are not cheap.  How accurate do you need to
>be?
>
>Sherpa Doug
>
>> {Original Message removed}

2001\11\14@181726 by Gennette, Bruce

flavicon
face
There are lots of cheap sensors available; photo transistors (MEL-12), photo
diodes (even a standard red LED can be used), simple transistor or op amps
can be used to boost the sensitivity to any reasonable level you require.
But they all suffer from ambient problems.

When mounted in a long tube (to block ambient light from the sides) they
have a very limited view window.  When mounted at the focus of a parabolic
reflector the angle is increased, but so is the ambient pick-up.  How can
you get around this?

Work out the geometry of your desired view zone and place a few sensors 'out
in the open' to pick up the average ambient light.  Mount a few more in
about the same positions, but blocked from the area of interest.  Mount a
main detector in a parabolic reflector that fully covers your area of
interest.  This gives you [+target +ambient], [-target +ambient] and
[+target].

A good choice is an old fashioned head light reflector with one pick up at
the focus and another six (3 shielded) around the rim.  Real old ones have
very wide pick up.  Sum the ambient sets with op amps and you get 3 signals
to feed to a cheap PIC for logging (or processing and displaying in real
time).

Bye.


{Original Message removed}

2001\11\14@201049 by Friedel Bruening

flavicon
face
What you wanna do sense with it ?
Friedel

At 10:16 a.m. 15/11/01 +1100, you wrote:
{Quote hidden}

>{Original Message removed}

2001\11\14@201323 by Friedel Bruening

flavicon
face
I have measured light down to 0.001lx, it´s not very difficult,
it uses a photo diode, an OP-Amp, feedback resistor of something around
256M, a small cap, and D/A converter minimum 16bit, may be autoranging
circuit depending what total range you are looking for.
You not only can measure the absolute value, but you can tell the amount
of light received per hour, or xhours.
The secrets are in the sensor arrangement, and may be the diode type.
I can help you with just everything, even with a ready to work device.

Friedel Bruening
Bolivian Instruments
Casilla 4856
Santa Cruz - Bolivia
Phone : 00591-773-92119
Fax : 00591-3-3580572
e-mail : spam_OUTbolinstTakeThisOuTspamcotas.com.bo

At 04:35 a.m. 15/11/01 +0800, you wrote:
{Quote hidden}

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2001\11\14@220952 by Peter Grey

picon face
At 08:52 PM 11/14/2001 -0600, you wrote:

Thanks for this. I am now waiting on some feedback to tell me the total
range required and the accuracy. I will come back to you following that.

Peter
{Quote hidden}

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2001\11\15@040259 by Raymond Choat

flavicon
face
I am very interested in your project as it sounds close to something I am
doing. I live in Kenai Alaska and want to be alerted when the northern
lights are out so I dont miss the free light show. If it works good enough I
wanted to put out an automated email alert over the internet to people that
sign up for it (NO SPAM) and to graph the sensor for everyone to see. I was
told I also might be able to do this by watching the magnetism of the earth
in my area.
Wrong Way Ray (Raymond Choat)
rcspamKILLspamkenai.net

{Original Message removed}

2001\11\15@114039 by Friedel Bruening

flavicon
face
I have heard that the VLF (Very Low Frequeny) activity would give you
give sure signs of this type events.
You ever heard of that.
There are sites about VLF, you may have a look into this and tell me
if you find something useful.

Friedel


At 12:03 a.m. 15/11/01 -0900, you wrote:
>I am very interested in your project as it sounds close to something I am
>doing. I live in Kenai Alaska and want to be alerted when the northern
>lights are out so I dont miss the free light show. If it works good enough I
>wanted to put out an automated email alert over the internet to people that
>sign up for it (NO SPAM) and to graph the sensor for everyone to see. I was
>told I also might be able to do this by watching the magnetism of the earth
>in my area.
>Wrong Way Ray (Raymond Choat)
>.....rcKILLspamspam.....kenai.net
>
>{Original Message removed}

2001\11\15@123124 by Harold M Hallikainen

picon face
       I really like the light to frequency converters from TAOS.  I've now
used a few thousand of the TSL235.
http://www.taosinc.com/pdf/tsl235.pdf

Harold

On Thu, 15 Nov 2001 04:35:42 +0800 Peter Grey <EraseMEmartechspam_OUTspamTakeThisOuTOZEMAIL.COM.AU>
writes:
{Quote hidden}

FCC Rules Online at http://hallikainen.com/FccRules
Lighting control for theatre and television at http://www.dovesystems.com

________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today!  For your FREE software, visit:
dl.http://www.juno.com/get/web/.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\11\15@183158 by Gennette, Bruce

flavicon
face
EPE magazine prints a how-to article every year.  Next month's issue,
according to the coming soon section in the November edition, will deal with
interfaces to the real world, with a focus on light intensity.  I suggest
you have a look in about 2 weeks.

http://www.epemag.wimborne.co.uk/

Bye.


       {Original Message removed}

2001\11\15@193440 by Friedel Bruening

flavicon
face
It looks nice, but what I don´t know, and I cannot figure it out from the datasheet
either, how much light does it need to work, what is the minimum light level,
there may be the problem, because night sky may give some lx when the moon
is up and big and sky is clear, but if not you may have 0.0.... lx or less. So
it depends on what is needed. The spectral response curve also isn´t really what
you would want for the task.
Anyway, seems a nice part, I have done se same, just lot bigger using standard
parts.

Friedel

At 08:47 a.m. 15/11/01 -0800, you wrote:
{Quote hidden}

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\11\15@213106 by steve

flavicon
face
> It looks nice, but what I don´t know, and I cannot figure it out from
> the datasheet either, how much light does it need to work, what is the
> minimum light level, there may be the problem, because night sky may
> give some lx when the moon is up and big and sky is clear, but if not
> you may have 0.0.... lx or less. So it depends on what is needed. The
> spectral response curve also isn´t really what you would want for the
> task. Anyway, seems a nice part, I have done se same, just lot bigger
> using standard parts.

The sensitivity to light and spectral curve are functions of it being a
silicon sensor. Unless you add filters (which will reduce the overall
sensitivity anyway) the spectral response will be the same for any
silicon sensor. The limiting factors are the sensitive area and
temperature. PIN diodes come in a variety of (large) die sizes to
give you more collection area. The problem is that they are just as
sensitive to heat and you have more heat collecting area as well.
You can see from the datasheeet for the device that heat is the
limiting factor as the light levels get low.
The sensitivity is given in the datasheet as uW/cm^2. One lux is
about 5uW/cm^2 (they aren't directly related but that is a guide). A
moonlit night is around 0.2 lx and a starlit scene about 0.01 lx.

You may want to experiment with LDR's. I was using one in a
project and noticed that it was really sensitive to changes at low
light levels. ie. There was a difference between being in a closed
drawer inside one piece of black heatshrink and having two layers
of heatshrink. I didn't investigate any further than that though.

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: @spam@stevebKILLspamspamtla.co.nz      fax +64 9 820-1929
======================================================

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\11\16@104625 by miked

flavicon
face
I'm still waiting fro the local Barnes and Noble
to get the October issue in.
> EPE magazine prints a how-to article every year.  Next month's issue,
> according to the coming soon section in the November edition, will
> deal with interfaces to the real world, with a focus on light
> intensity.  I suggest you have a look in about 2 weeks.
>
> http://www.epemag.wimborne.co.uk/
>

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email KILLspamlistservKILLspamspammitvma.mit.edu with SET PICList DIGEST in the body


2001\11\16@121635 by Harold M Hallikainen

picon face
On Fri, 16 Nov 2001 15:23:53 +1200 Steve Baldwin <RemoveMEsteveTakeThisOuTspamTLA.CO.NZ>
writes:
>
> You may want to experiment with LDR's. I was using one in a
> project and noticed that it was really sensitive to changes at low
> light levels. ie. There was a difference between being in a closed
> drawer inside one piece of black heatshrink and having two layers
> of heatshrink. I didn't investigate any further than that though.
>

       What has been your experience with repeatability with LDR's? My
experience with CdS LDR's has been less than spectacular. They have a
"light adapted" resistance that is different from the "dark adapted"
resistance.

Harold


FCC Rules Online at http://hallikainen.com/FccRules
Lighting control for theatre and television at http://www.dovesystems.com

________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today!  For your FREE software, visit:
dl.http://www.juno.com/get/web/.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spamBeGonelistservspamBeGonespammitvma.mit.edu with SET PICList DIGEST in the body


2001\11\16@161149 by Peter L. Peres

picon face
> 0.1lx

You will need a large area photodiode. A solar cell may work. You will
have to measure currents in the nA region, using opamps powered by a
battery and make it stable over temperature (portable instrument I
suppose), and null the effects of condensation and weather (humidity etc),
which can upset such measurements. This can be done but it requires some
work esp. in the analog section and the packaging section.

Of course a PMT would solve the problem immediately but I do not suggest
this (fragile, expensive, bulky, needs HV to run, can be damaged by
excessive light). In theory you should be able to get at least 1/10 of the
performance of a PMT by using a silicon solar cell of the same area as the
PMT. Unlike the PMT the silicon cell will also sense some infrared and
ionizing radiation. This could falsify your measurements.

Wrt. detecting northern lights, good luck keeping the haze of the street
and city lights out of the picture, and the lens (if any) unfogged and
unfrozen. Such instruments are usually mounted in small (or larger)
geophysics and other observatories which are placed way up the wazoo up on
mountains, over the bridge, etc., precisely to remove the chances of
someone's $2 pocket flashlight making interesting recordings in a
nation-wide read chart.

On the other hand, the local university or weather station people (if any)
could help you out here, by co-locating your equipment or something like
that. If not, then find a friend with a hunting lodge in the right place
(beyond a wooded hill from a city is right if the city is small -else 10
hills or more imho).

Peter

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email TakeThisOuTlistservEraseMEspamspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body


2001\11\16@161158 by Peter L. Peres

picon face
Friedel Bruening <RemoveMEbolinstspamTakeThisOuTCOTAS.COM.BO> wrote:
> I have heard that the VLF (Very Low Frequeny) activity would give you
> give sure signs of this type events. You ever heard of that. There are
> sites about VLF, you may have a look into this and tell me if you find
> something useful.

Come to think of it, it does not need to be VLF. I heard that aurora
borealis makes a lot of noise on HF so a shortwave receiver tuned on an
unused frequency should work. Maybe even LW broadcast receiver.

Peter

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservEraseMEspam.....mitvma.mit.edu with SET PICList DIGEST in the body


2001\11\16@161216 by Peter L. Peres

picon face
I just had an idea. Could you not use a camera. A CCTV camera with an
integrator fitted after it would do the trick imho. It could even
deliberately remove point sources (moon, bright stars) in the image using
a simple analog peak detector & switch combination. Or use a computer to
interpret the image and do all the tricks (possibly remotely - using a
dedicated web server to supply the images for example - this also
applies to the northern lights, a skycam and some processing software
would do the trick, plus everyone can watch the website itself ...).

You can now buy inexpensive CCTV cameras that do 1lux and less. They will
likely resolve 0.01lux with an integrator without too much trouble.
Temperature will have to be taken into account probably. The cameras
already do the log trick (gamma) but they are not so accurate at that. AGC
and iris will have to be fixed.

Peter

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email EraseMElistservspammitvma.mit.edu with SET PICList DIGEST in the body


2001\11\16@162852 by steve

flavicon
face
>         What has been your experience with repeatability with LDR's?
>         My
> experience with CdS LDR's has been less than spectacular. They have a
> "light adapted" resistance that is different from the "dark adapted"
> resistance.

I couldn't really comment further than saying it was adequate for
the application. My need was to set a threshold around dark
adapted vision which is a blurry line anyway (even if you could see
it). I also had plenty of time which may be a factor.

Steve.


======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: RemoveMEstevebEraseMEspamEraseMEtla.co.nz      fax +64 9 820-1929
======================================================

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email RemoveMElistservspam_OUTspamKILLspammitvma.mit.edu with SET PICList DIGEST in the body


2001\11\16@200430 by Friedel Bruening

flavicon
face
At 08:31 p.m. 16/11/01 +0200, you wrote:
> > 0.1lx
>
>You will need a large area photodiode.

No you don´t, I have measured 0.001lx with 1.4mm2 surface
foto diode, OP-AMP and feedback resistor, measuring
pA´s (10-11).
The solar cell no is nothing more than a foto diode.

Friedel

{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email EraseMElistservspamspamspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body


2001\11\16@201058 by Friedel Bruening

flavicon
face
The problem with LDR´s is that they are pretty slow, and show
a kind light memory effect, which can be troublesome, than
the other problem could be linearity and the spectral response.
LDR´s make sense when cost is most important, and all the
disadvantages are not so important.

Friedel


At 08:53 a.m. 16/11/01 -0800, you wrote:
{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spamBeGonelistservSTOPspamspamEraseMEmitvma.mit.edu with SET PICList DIGEST in the body


2001\11\17@043656 by Raymond Choat

flavicon
face
Is that what HAARP puts out?  I will check it out and let you know if I find
something. So far I know I can sense the northern lights by sensing the
light or the earths magnitism. The plasma hitting the ionisphere causes both
of these to change.
Thanks Wrong Way Ray (Raymond Choat)

{Original Message removed}

2001\11\17@092429 by artstar

flavicon
face
Sort of, using massive class C and D amplifiers if I remember correctly.
But if I remember correctly, I think it was actually high powered
microwave radiation to try to excite the ionosphere such that it created
an electromagnetic shield. Of course, many a political activist have
always felt otherwise, and I guess that feeling is compounded upon with
the US military's secrecy about the whole project. They haven't let on
much. Only these given details thus far.

Adios,
LarZ

---------------  TAMA - The Strongest Name in Drums  ---------------

{Original Message removed}

2001\11\18@185448 by Peter L. Peres

picon face
A photodiode with 1.4mm^2 working at 0.01lx will as you said work in the
pA region, and require a 256M resistor (as you said - quick go buy one
from Digi-Key), as well as a special opamp. When you expose this to cold
(under dewpoint) you have condensation that can conduct 1000 times more
than your pAs on the board.

So you use a large photodiode (solar cell), which moves the problem into
the tens of nA region (1000 times less problems), will likely work with a
10M off the shelf feedback resistor and an off the shelf inexpensive
opamp. In both cases temperature compensation is required, probably by
using a differential arrangement using two identical sensor devices, one
completely shielded.

Due to the lower environmental requirements my implemntation would be
reproductible and relatively inexpensive to make and operate. To
compensate and shield something that runs in the pA range over -55 to
+100C and humidity 0 to 100% while keeping an optical window clean at
all times is a very expensive and laborious enterprise. Doing this for
something in the nA range is feasible (I know that for sure). Even so an
ITO heated optical window will probably be unavoidable.

Peter

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2001\11\19@130436 by Friedel Bruening

flavicon
face
At 11:00 p.m. 17/11/01 +0200, you wrote:
>A photodiode with 1.4mm^2 working at 0.01lx will as you said work in the
>pA region, and require a 256M resistor (as you said - quick go buy one
>from Digi-Key), as well as a special opamp. When you expose this to cold
>(under dewpoint) you have condensation that can conduct 1000 times more
>than your pAs on the board.

When I did this, I needed the small surface for some reason, it was an instrument
for fotolab application, measuring light in the certain parts of the projected foto,
which was amplified to about life measure and environmental requirements
didn´t matter so far, as the measurement where relative, not absolute.
The amplifier was a CA3140, nothing special, later I used TLC271, which turned
out to have a lot lower TC, but why don´t you look into INA114 or INA116,
a very good/compact differential solution, very stable, bit expensive but gets
you out of a lot of trouble for sure.


>So you use a large photodiode (solar cell), which moves the problem into

I wouldn´t now how the low light level response and noise relation is,
spectral response of common solar cells. Anyway, have a look into
HAMAMATSU, excellent supplier of fotodiodes with all kinds if
spectral response, size, etc., you might be served better using
devices as such.


>the tens of nA region (1000 times less problems), will likely work with a
>10M off the shelf feedback resistor and an off the shelf inexpensive
>opamp. In both cases temperature compensation is required, probably by
>using a differential arrangement using two identical sensor devices, one
>completely shielded.

You might head the complete sensor, as we did earlier with the crystals
to maintain them stable. running them at 70ºC, using a power transistor
mounted to them, what we call a crystal oven, with your sensor your case,
it´s probably a reverse, you might want to keep it cool, if noise would be
a problem.

Friedel

{Quote hidden}

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...