Like many others here, I have barcode scanners, thermal receipt printers, and cash drawers working now. It took a bunch of testing to find stuff that worked though. The biggest problem was that Microsoft Windows was really the only operating system I could use to get it all to work as a cash register.
The thermal receipt printers do the work of opening the cash drawer for you. They have a small connector cable that goes from the drawer to a port on the thermal receipt printer. The windows drivers for the printer have settings available to tell the printer when to open the drawer (before printing receipt, after print, or not at all). These printers do NOT work well on any other operating system that I could find. All of the linux systems rely on modified versions of CUPS to drive the printers and then you cannot get the cash drawer to open. Some printer manufactures publish source code that you can “sometimes” get to compile inot a set of files used in CUPS configurations, but of the 3 that I tried, I could not get any to work properly with the drawer.
There are plenty of cheapo scanners you can use to scanning the UPC barcodes, but if you get the cheap ones from china, expect to replace them every few weeks. They are pretty fragile and the first time an employee drops it on the counter or the floor, it may stop working, or worse, it may read incorrectly. To get past this I used only the Motorola LI4278 scanners. I have them even in the warehouses. I have seen one dropped down a whole flight of concrete steps and it still worked. You can normally get the 3 year overnight replacement waranty on them for another $90 or so. I did this for about a dozen of them deployed. over the past 3 years only had to use the service on two of them (on was dropped from 11 feet and wouldn’t work anymore, the other stopped working after being left in the rain on hte dock in a ligthtning storm).
I have not yet found a card reader that will work. There is no ready-made interface software that you can throw in place for ERPNext in a hurry. For now we use external card terminals and only complete the sale in ERPNext POS if the charge goes through.
Good Luck,
BKM