Quantity   Component name
1 × Arduino Pro Micro Really any Arduino Leonardo-compatible device
1 × TTL - to - RS232 Module An interface between TTL TX/RX serial signals and RS232C-level signals. Many possible solutions from hand-build boards using any number of converter ICs to modules found on ebay, or in my case at my makerspace as part of some obsolete development system.
2 × 10 k-ohm resistor
1 × 0.1 uF capacitor
1 × schottky diode This diode isolates the printer power supply from the Arduino supply. It should have as low of a Vf as you can find. It doesn't have to deal with much current, probably less than 50 mA.
1 × Proto board and misc cabling A proto board to hold the various modules and cabling to connect to the printer.