I was looking at doing this as well and found the following formula posted in Discussions:
Barcode Key Field (This field used to calculate a barcode number)
ToNumber("[Store #]")&
[Record ID#]&
[Related Store]&
[Equipment Type]
Barcode Link (URL Formula)
"http://www.keepautomation.com/online_barcode_generator/linear.aspx?DATA="&[Barcode Key]&"&TYPE=7"
Barcode Image (Text Formula)
"<img src=" &[Barcode Link]& ">"
Here is the link to the full discussion.
https://community.quickbase.com/discussions/quickbase-discussions/can-you-generate-a-barcode-from-a-key-field-calculation/52210
We ultimately chose to go another route so I didn't actually end up implementing. Hope this gets you started.