Low cost image sensor

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Hi,
I have been searching the web for a low cost image sensor.
The application is for reading a type of barcode, approximately 20mm x
5mm, but I could make do with an area as small as 10mm x 3mm. A
resolution of 0.1mm would be more than adequate, and I only require
monochrome. Ideally I would like no moving parts, and no lens. The item
to be scanned would be placed directly on the sensor, illuminated from
behind.

I have found something like the VV6501C001 from STMicroelectronics,
cheap enough for this application <$6 US, however the array size is 3.6
x 2.7 mm, and the resolution is much higher than I need, although this
is not a problem. Unfortunately the physical package does not allow
these to be stacked in a linear array, or else I could use 3 or four of
these type of devices.

Any suggestions would be appreciated, for this to be cost effective, we
are looking at a maximum of $20US in small quantities.
Thanks,
Allenb


Re: Low cost image sensor
On 28 Jun, in article
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Are you really reading a 2D barcode as compared to normal 1D barcodes?
In other words is the important factor the 20mm dimension which has to be
read to 0.1mm resolution which actually means a minimum of 200 pixels
realistically 400 pixels would be better to ensure the resolution.

You need a square pixel device for certain (not all are).

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No lens at all or built in lens? There are plenty fo cheap lens manufacturers
who no doubt make something you could use.

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Why are you looking at an area scan (VGA res) device? Most 1D bar code
scanning is either

a)   Moving optics and single photodiode sensor

b)   Line scan camera chip and simple lens

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IF you scanning a 1D barcode and its orientation (matching in plane but
may be mirrored), then kook at Line scan devices from manufacturers such
as  Sony, Silicon Video Inc and others.

Last time I had a quote was for a 1024 pixel line scan from Silicon Video
for less than 14 pounds in UK (about $18) for TWO devices.

These types of devices are used all other the world in lots of equipment
bar code scanners, copiers, faxes, even desktop scanners and many other
places in industry.

--
Paul Carpenter          | snipped-for-privacy@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/ PC Services
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Re: Low cost image sensor
Hi Paul,
Thanks for the reply.

Paul Carpenter wrote:
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This isn't a standard bar code, however the resolution in the Y
direction is much less critical, it only needs to be about 0.5mm. For
the X direction, 200 pixels would be more than adequate.

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The final product, will be a small handheld battery operated device,
the item to be scanned is placed on it, a button is pressed, and the
result is displayed on an LCD. The reason why I mentioned no lens, is
for mechanical simplicity and compactness, if the item is placed
directly on the lens, I would imagine that the sensor would need to be
some distance away.
Thanks,


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Re: Low cost image sensor
On 28 Jun, in article

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So you are using some form of effectively a 2D bar code where each line is
different. If not and the data is ONLY ONE line of information, then the
vertical resolution only effects the vertical size of the sensor to be
less than image size vertically. Thus acquiring images are more likely
to be within the vertical size of image ensuring not averaging foregrround
and background as one pixel.

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For 200 pixels to be sufficient your image only needs 100 actual defined
points. At 0.5mm resolution vertically you are having about 10 'lines' of
information. I do hope you don't expect to require 200 pixels image
resolution of the object and to get that from a 200 pixel device. Most
people doing measurements using video devices rely on 5 to 10 times the
pixel resolution required to be sure where the edges ACTUALLY are and
to reduce mechanical alignment issues.

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...

Lens focal distance depends on many issues including sensor size. To
use no lens at all then either you are using

a) pin hole camera with need for LOTS of light for SHORT exposure time

b) Sensor has a 1:1 match that is registered EXACTLY between sensor and
   code being scanned.

Otherwise you WILL get out of focus images. None of this is mechanically
simple as it requires precise registration of object to sensor for
orientation, distance and perpendicularity.

Consider even standard Line scan devices like Sony ILX511 have a pixel pitch
of 14um for a 2048 pixel device, and the Silicon Video Inc Elis-1024 has

        Resolution      Pixel
        mode            Pitch
        1024            7.8um
        512             15.6um
        256             31.2um
        128             64.4um

These are quite LARGE pixel pitches, without a lens of some sort you will
find it difficult to get 20mm or 10mm onto a sensor. Very FEW sensors are
stackable in H or V without special optics or overalaps from prisms and
optical paths.

At 100um (0.1mm) pitch this is too small for photodiodes to be stacked
and too large for most line or area sensors.

You will need some form of lens, and the size of sensor and lensing are
affected by object distance and field of view. With the following you get:-

Object size     20mm    10mm
Object distance 10mm    5mm
Imager size     28mm    28mm    (Sony ILX511 2048pixel line scan)

gives
Field of view    90     127     degrees
Focal length    14mm    7mm     (lens centre to imager)

Sit down and do some lens calculations based on what you object size and
distance are to determine from various imager sizes what the focal length
is. Then consider your arrangements.

--
Paul Carpenter          | snipped-for-privacy@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/ PC Services
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Re: Low cost image sensor
Hi Paul,
Thanks for the comprehensive explanation. I was hoping to get by with
something simple, hoping that I could find an array type device with
about 200 by 30 pixels, on a 0.1mm pitch. That way I could avoid the
complexities of lenses etc. However after reading your reply, I realise
that I probably will need to look at a lens based system.
Thanks again,
Allen.

Paul Carpenter wrote:
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manufacturers
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