Barcode Symbologies

Seconded.

It's well-known that "security by obscurity" doesn't work. The OP is looking for disambiguity by obscurity. That won't work either, for roughly the same reasons.

Ah, OK. I.e., "read the barcoded label" instead of trying to read a serial number off a board, etc.

Understood. Sort of like "unlock codes" for software...

Oh. So you just used "001", "002" and "003" out of 999 valid codes (?).

I'll see if I can find three or four "compatible" scanners (compatible in terms of their feature sets). If all of them have the feature, that gives me three "backup suppliers" if one goes belly up.

Correct.

Therein lies the rub. I.e., you can calculate the chances of a fuse blowing given a particular nominal load; you can calculate the time it takes to respond to an interrupt event; etc. -- but this sort of thing is really hard to quantify. All you can do is try to make it "highly unlikely" that you'll have a conflict in practice. And, design so that the only thing you need to change are the *physical* labels if a conflict becomes commonplace.

What happens if the barcode vendors decide that RFID is pushing them out of the market (once tags get cheaper) and decide to stop manufacturing scanners?

Why doesn't UPS, FedEx, your local library, Dell, etc. use UPC and "register"? It's a manageable risk. Just like every other engineering decision.

The real reason is, UPC is registered for commercial reasons. It is a barcode format that is written by a producer and is intended to be read by potentially many consumers.

Your problem appears to me to be once written, it is intended to be read by a limited number of consumers. The kind of application you described can be reliably implemented using record syntax and minimal record checking probably a single character. I can tell you from experience that false positives are very rare. "Contemporary applications of optical bar code technology" Banks,Helmers,Trueblood Library of Congress HF5416 .B36

My choice for your application would be Code39. I would like to have a total record size of 12 - 15 characters.

Codabar has a slightly higher density than Code39 with fewer symbols. Actually it has be sometimes known as 2 of 7. It has some big users (FedEx for example). The plus for you is it has multiple record field separator characters that have no data meaning.

Regards,

Walter..

-- Walter Banks Byte Craft Limited

I think you are barking up the wrong tree here, let the scanner spit out lots of invalid for you codes and you sort them out. It is not like they are spitting hundreds of codes per second. And use any 2D code, then your subset acceptable code space can have huge Hamming distances. Plus there is enough internal code space to put internal ECC in.

Yep, and there are label printers for doing just that.

The problem with those is they allow you to print *any* label "at will" (i.e., without the "system" being aware of the label being issued).

They also tend to be thermal (dye transfer) so supplies are more costly. (I've a pile of portable and small desktop thermal label printers getting ready for the recycle bin) As well as the hassle of recharging batteries, etc.

And, you need "another" general purpose printer to print your "non barcode" items (i.e., now you have to stock supplies for two different printers).

For non-contact scanners at reduced density, easier to use a conventional printer to do that "double duty".