Low cost image sensor

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).

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

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

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.

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.

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,

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.

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.

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