Why not use a Barecode Reader to add products on your shopping list?
Step 1: Get a Barcode Reader
You can get one on amazon, in this tutorial it's the « Inateck 2.4GHz Wireless USB Automatic Barcode Scanner Handheld Bar-code Reader »
Step 2: Connect Your Barcode Reader
Open the TimeSquAir (4 nylon screws on the back) and plug the USB dongle of your Barcode reader on the Raspberry Pi.
Step 3: Collect the Data
Then on Node-RED, take the node "Serial" in the input section. Create a new Serial Port and set it like the picture.
Step 4: Transform a Binary Code Into a String
Now if you use your Barcode, it'll return something like that : «02000700000000000000000000000000...»
If you want to translate this binary code into characters you just need to create a function that will do it.