You may not need any plug in. It depends on the barcode you wish to use.
Barcodes in software such as Filemaker are just special fonts that show bars in place of the normal characters. You can simply enter the number you want into a text field and a different copy of the same field can specify the barcode font to produce the barcode labels. A plug in might come in handy for barcodes that incorporate and error check character in the barcode thus produced if that's something you want. A plug in can also be useful for scanners such as the camera in a an iPhone or a digital camera are used to scan the barcodes instead of using a barcode scanner connected directly to your computer with USB.
A typical Barcode scanner connected vis USB functions in "keyboard emulation mode". That means that the data scanned by the barcode is input into the computer as though those barcode characters where typed in at the keyboard. And these same scanners can usually be configured to append additional characters to the beginning and end of the scanned data.
These extra characters can be used with FileMaker script triggers to automate the scanning process. A special character at the beginning of the scanned data can be used to trip the OnLayoutKeystroke trigger and the script it performs can put the cursor into the correct field to recieve your scanned data. A return, tab or enter character at the end of the scanned data can be used to trip the OnObjectExit trigger on this field and thus perform a script that checks your scanned item in or out of your library.
The basic elegance of this approach is that if your scanner doesn't work or if the barcode label is damaged and thus can't be scanned, you can still put the cursor in the field and manually type in the barcode number and then press return, tab or enter to exit the field to check the item in or out of your library.
May be of interest
Scanning Barcodes and More with FileMaker Go – Part 1
October 8, 2012 This is Part 1 of a 3-part series.
CNS Barcode Plugin $10
Need help writing script to integrate barcode scanning
Title: Need help writing script to integrate barcode scanning
Video from SkeletonKey about FMP Barcode Scanning
You are correct about the scanner acting as a keyboard. I have bought the CipherLab 1660 (Bluetooth) which does just that. A problem has now arisen...because its bluetooth, and it registers as a keyboard it wont allow the built in iPad virtual keypad to operate!
So, I can either have a barcode scanner and not be able to enter any other data (the application is for a site survey audit), or I can manually type the barcode and be able to enter the rest of the data too. Of course, having the barcode is pretty important so other users can "Seach" for the item to see if has already been registered.
I can connect my Belkin bluetooth keyboard and type into fields, but that means I have to rotate the whole assembly everytime I want to type! Not very ergonomic...
Does anyone have any ideas as to how the internal iPad keyboard can be switched on even when a bluetooth keypad is connected?