Point of Sale
How to Connect a Barcode-Printing Scale to Your POS
Most shop owners assume connecting a weighing scale to a computer means a cable, a driver, and a technician's visit. It doesn't. If your scale prints barcode labels, it is already talking to your POS — you just have to teach the POS to listen. Here's how it actually works, and how to set it up on YellowPOS in about ten minutes.
The label is the cable
Look at the back of a typical barcode-printing scale — the TM-A models common in Lebanese groceries, or an Aclas, Rongta, DIGI, or CAS — and you'll see a USB port, an RJ45 socket, and an RS-232 serial port. It's tempting to think one of those is how you plug it into the till. In practice, on this class of scale those ports are mostly for loading your product list into the scale, not for streaming live weight out of it.
The real integration channel is the sticker. When the scale weighs your cheese and spits out a label, the barcode on that label is not a normal product barcode. It's a little data packet, and the weight is inside it.
What the digits actually mean
Retail barcodes reserve a prefix — nearly always 2 — for "in-store use". Anything starting with 2 is not a manufacturer's product code, so a store is free to put whatever it wants in the remaining digits. Scales use that freedom to pack in two facts: what was weighed and how much it weighed.
A very common layout looks like this:
A cashier scanning that barcode is really handing the POS the sentence "1.352 kilos of item 21". At $12.00 per kilo, the line is $16.22. That's the entire trick.
The PLU is just the short number you press on the scale to pick a product — 21 for feta, 22 for halloumi. Every barcode-printing scale has this concept.
Why most POS systems make this painful
There's no single standard. One scale writes 5 PLU digits and 5 weight digits; another writes 4 and 6; another puts the price in there instead of the weight; another writes grams where its neighbour writes tenths of a gram. Plenty of POS software hard-codes support for a handful of brands — and if your scale isn't on the list, you're stuck.
So YellowPOS doesn't hard-code anything. Instead you describe your scale's layout with a short pattern called a mask:
- A plain digit (like
2) must match exactly — it's what flags the barcode as a scale label. - I — a PLU digit.
- V — a value digit (weight or price).
- C or X — ignore (check digit, filler).
The example above is 2IIIIIVVVVVC. A scale with a different layout is a different string of letters — not a different version of the software.
Setting it up: about ten minutes
1. Mark the product as sold by weight. Edit the product and set its unit to kg. Its price now means "price per kilo" and its stock is a weight.
2. Give it the PLU. Add the scale's PLU (e.g. 00021) as a barcode on that product, using the barcodes field you already use for normal products.
3. Describe the format. In Settings → Weighing scale, switch it on and enter your mask, whether the value is a weight or a price, and the divisor (use 1000 if the scale writes grams and you sell per kilo).
4. Test it with a real label. This is the step that saves you the headache. There's a tester built into the settings page: weigh something, take the label the scale actually printed, and type its digits in. YellowPOS shows you the PLU it read, the product name it matched, and the weight it calculated. If the name and weight are right, you're done. If not, tweak the mask and try again — the tester reads the live form, so you never have to save-and-pray.
What you get at the register
- Scan and go. The line shows
1.352 kg × $12.00 = $16.22. Scan a second piece and the weights add up. - Stock in grams. Sell 1.352 kg out of 10 kg and you have 8.648 kg left — not "9 pieces".
- Normal barcodes untouched. The POS tries an ordinary product match first, so your packaged goods behave exactly as before.
- Works offline. Scanning and decoding happen on the device. If the internet drops mid-shift, you keep selling and the orders sync later.
- No scale? No problem. Tap a weighed product and type the weight, or edit the quantity to
1.35on the order line.
Frequently asked questions
How does a barcode-printing scale connect to a POS?
Through the label, not a cable. The scale prints a barcode with the product's PLU code and the weight embedded in its digits. The cashier scans that label with a normal barcode scanner, and the POS decodes the digits to know which product was weighed and how much it weighed. No cable, no driver, no serial port.
What is an embedded-weight barcode?
It is an EAN-13 barcode that starts with a store-use prefix (usually 2) and carries data instead of a manufacturer's product number. A typical layout is 2 + a 5-digit PLU + a 5-digit weight in grams + a check digit. So 2 00021 01352 means item 21, weighing 1.352 kg.
Do I need to buy a new scale to use this with YellowPOS?
No. If your scale already prints barcode labels, it will work. YellowPOS lets you describe your scale's barcode layout in settings rather than hard-coding support for specific brands, so models like TM-A, Aclas, Rongta, DIGI, and CAS are all covered.
Does the scale need internet?
No. The scale is a standalone device that just prints stickers, and scanning those stickers at the POS is handled on the device itself. The whole flow keeps working during an internet outage; orders sync once you are back online.
What if my scale prints the price instead of the weight?
That is supported too. Some scales compute the total price and embed that instead of the weight. YellowPOS can work backwards from the price and the product's per-kilo price to recover the weight, so stock still decrements correctly.
Try it with the scale you already own
Scale support is currently in beta — the format is configurable precisely because there are so many models out there, and we want to hear about the ones that don't fit. The full walkthrough is in the Weighing Scale guide, and if you're weighing up a POS in general, our take on the best POS for Lebanon covers the rest. Every plan includes a 1-month free trial.