Basically, my phone has a bunch of money apps (Square Register, PayPal, Bitcoin, etc). I'm taking a cheap ~15 year old cash register and hooking it up to my phone so I have a big keypad and cash drawer.
Moto X 2013 phone
Other phones will work fine too, but mine is the same size as the register screen
Royal ER 125 Cash Register
Remove years of filth before using
USB OTG cable
90 degree connector recommended
For converting the register keys to USB keyboard, and opening the cash drawer
It was really easy to take apart. There were only two screws on the back holding it together. Once I took them out, I was able to lift the plastic part off the base and disconnect the wires from the main board, which slides in and out on a groove. After I removed all the components, I washed the plastic parts out.
Here's the main board (top end at bottom of frame):
And the keyboard board with rubber pads:
I used the water hose again on the keypad membrane thing.
I removed the receipt printer assembly. I don't plan on reusing it.
For some reason, the register has a holder for 4 AA batteries next to the receipt paper. It hooks into the main board, but the whole thing still needs to be plugged in. I think it might be for persistent memory or something. I'm going to use it to power the Arduino (and possibly charge my phone). This has a date with the hose too. Anybody know why it warns to plug in the register before inserting the batteries?
All that's left is the cash drawer. Those two wires trigger some kind of solenoid that releases the drawer so a spring pushes it out.
I used a sponge on this part, because I didn't want to remove the parts inside. I blew it out with an air compressor instead of the water hose.
Finally, here's all the big pieces laid out:
Next time, I'll show what it looks like with a fresh coat of paint.