An Old Cash Register Repurposed as a Hotkey Keypad

Because the technology has pushed forward, it’s easy to find cheap used cash registers. Fwacer repurposed one of those into a hotkey keypad.

Cameron Coward
5 months agoUpcycling / Productivity

“Necessity is the mother of invention,” as the old proverb goes. That means we most often see technology flourish first where it is most practical. For instance, digital computers were first developed before and during World War II specifically for the war effort to calculate trajectories and to assist with cryptography. In the civilian world, cash registers are a great example of technological innovation. Complex electromechanical cash registers were in use up until the digital era when computerized cash registers quickly took over. Because that technology has pushed forward, it’s easy to find used cash registers for very little money. Fwacer repurposed one of those into a hotkey keypad.

In their tutorial, Fwacer explains that they had been planning to build a custom hotkey keypad for a while when they came across an old all-in-one cash register in a pile of free e-waste. An important feature for cash registers from this era was the use of keys with replaceable labels. If a McDonald’s fast food restaurant decided to discontinue the McRib rib and replace it with a Shamrock Shake, they only had to replace the label and reprogram that entry for employees to add it to orders. That’s also very handy for a hotkey keyboard, and it certainly doesn’t help that this particular cash register had nice mechanical key switches.

To utilize it, Fwacer first removed the keypad from the cash register. They then thoroughly cleaned the keys and panel. With a clean keyboard, they set out to reverse-engineer the keyboard matrix layout. That process is time consuming, but can be completed with methodical multimeter testing. The columns and rows of that matrix can then be connected to a development board. Fwacer used an Arduino Pro Micro, which is ideal because it can be configured to appear as a USB HID keyboard when it’s connected to a computer. Keypress combos can be configured in firmware, and shortcuts can be setup on the computer. The final step was the build the enclosure, which Fwacer constructed out of MDF cut by hand. With some paint and new key labels, Fwacer has a high-quality hotkey keypad with a plethora of keys for all kinds of productivity fun.

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