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| olliH... |
 Posted: Thu Sep 03, 2009 3:30 am |
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Hi,
i have a question regarding to photodiode arrays. I would like to
detect a laser beam's position on a photodiode array.
I'm looking for a nice circuit to proccess the generated currents.
Until now the only solution i know is to amplify all the currents
generated by the photodiodes and calculate the position by finding the
centre of gravity.
It would be great if somebody knows a circuit that manages the same
problem with only two ADCs and two current to voltage amplifierts.
(like in a PSD)
Maybe it is possible with some resistors etc..?
One reason why i don't use a PSD is the size of them. Another is that
i want a scalable solution
If this is the wrong group.. who knows a good group for
optoelectronics?
Thank you for your time and consideration |
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| whit3rd... |
| Posted: Mon Sep 07, 2009 1:57 pm |
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On Sep 3, 6:30 am, olliH <oliver.hofh... at (no spam) googlemail.com> wrote:
[quote:52fcf8082c]i have a question regarding to photodiode arrays. I would like to
detect a laser beam's position on a photodiode array.
[/quote:52fcf8082c]
A lot of gizmos can 'detect' a position; with a four-diode array,
you can run stepper motors to position the sensor in X-Y space so
that the beam spot is centered on the array.
I presume you mean to use a linear array and do peak-finding?
Brute force, you digitize a lot of brightness values, do a curve-fit
to some appropriate lineshape (Gaussian? Sink function?)
and read off the center position of the fitted curve.
Center of gravity will NOT always work, there may be spurious
extra light from reflections etc., which is clearly not part of the
main image. Curve fitting won't be affected, but center-of-gravity
will. |
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| Bob May... |
| Posted: Thu Sep 10, 2009 2:42 pm |
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Might also mention that a "photodiode array" is a fancy term for a camera.
Even just to pointing a webcam at a wall with the laser beam hitting it!
--
Bob May
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net |
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| JohnH4... |
| Posted: Sat Sep 19, 2009 3:44 am |
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On Sep 3, 8:30 am, olliH <oliver.hofh... at (no spam) googlemail.com> wrote:
[quote:80b39a0b5b]... i have a question regarding to photodiode arrays. ...
[/quote:80b39a0b5b]
What kind of photodiode arrays? Examples? |
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| olliH... |
| Posted: Tue Sep 22, 2009 1:22 am |
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[quote:11ac8827b0]What kind of photodiode arrays? Examples?
[/quote:11ac8827b0]
Hi,
i would like to use a photodiode array like this one:
http://www1.silonex.com/datasheets/specs/images/pdf/103076.pdf
The laser source is a line laser like this one:
http://www.lasercomponents.com/us/laser_modules.html?&tx_bgmprodbfrontendlc_pi1[rid]=1339&cHash=0e4ef76635&MP=6-446
The beam profile will have a higher diameter then the width of one
cell. Because PSDs are very pricy and PSDs are not available in the
length I desire, I would like to use the mentioned photodiode array
and use maybe 2-5 of them in a row.
That would be the same as many pixels in a row. What i don't know is
how many pixels i will need but there could be easily more then 20.
That is why i want a circut that allows me to integrate more "pixels"
or.. photodiode arrays.
To use as many amplifiers and ADCs like there are pixels is to
complex. I want to be able to scale the number of pixels without
changing to much the circuit. |
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| Phil Hobbs... |
| Posted: Tue Sep 22, 2009 9:29 am |
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olliH wrote:
[quote:9a29637680]What kind of photodiode arrays? Examples?
Hi,
i would like to use a photodiode array like this one:
http://www1.silonex.com/datasheets/specs/images/pdf/103076.pdf
The laser source is a line laser like this one:
http://www.lasercomponents.com/us/laser_modules.html?&tx_bgmprodbfrontendlc_pi1[rid]=1339&cHash=0e4ef76635&MP=6-446
The beam profile will have a higher diameter then the width of one
cell. Because PSDs are very pricy and PSDs are not available in the
length I desire, I would like to use the mentioned photodiode array
and use maybe 2-5 of them in a row.
That would be the same as many pixels in a row. What i don't know is
how many pixels i will need but there could be easily more then 20.
That is why i want a circut that allows me to integrate more "pixels"
or.. photodiode arrays.
To use as many amplifiers and ADCs like there are pixels is to
complex. I want to be able to scale the number of pixels without
changing to much the circuit.
You might want to consider using one photodiode and a shadow mask,[/quote:9a29637680]
instead. It might need a lens as well. Position sensing doesn't come
cheaper than that.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net |
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| Bob May... |
| Posted: Tue Sep 22, 2009 2:34 pm |
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You might also want to try a camera array. These are available in megapixel
arrays with more than 1K pixels in each direction and take only a short time
to readout to one ADC. Nice thing is that you don't need to read out all of
the array to get what you need.
--
Bob May
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net |
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| olliH... |
| Posted: Wed Sep 23, 2009 1:30 am |
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a camera array could be nice.
What i want to do is build my own camera array  with the potodiode
arrays. I don't need to small pixels. 500 µm x 500 µm is fine for each
pixel.
I need a specialist for these type of circuits who can give me a hint.
Maybe a good book would be great. |
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| Bob May... |
| Posted: Wed Sep 23, 2009 2:55 pm |
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Linear arrays are usually read out serially. Get a catalg from several of
the makers of them and they usually have example schematics or tech notes
for the products. Linear arrays can be quite large as many of them are used
for flatbed scanners.
--
Bob May
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net |
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| Hazem... |
| Posted: Sat Oct 10, 2009 2:21 pm |
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On Sep 23, 7:30 am, olliH <oliver.hofh... at (no spam) googlemail.com> wrote:
[quote:4adf9a1149]a camera array could be nice.
What i want to do is build my own camera array with the potodiode
arrays. I don't need to small pixels. 500 µm x 500 µm is fine for each
pixel.
I need a specialist for these type of circuits who can give me a hint.
Maybe a good book would be great.
[/quote:4adf9a1149]
If you don't require much resolution, then just project the beam on a
screen, position a single CCD or CMOS camera behind the screen (or on
the same side as the beam image if you must), take a picture of the
screen, and you're done. As long as the camera's position is known and
constant, and if you've calibrated (mapped) the setup, you should be
able to use this technique to measure the location and length of the
laser line.
Hazem |
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