Toby Chui's 4x5Macro-Numpad Is a Fully-Featured Arduino-Compatible Macropad for Just $8

University student Toby Chui has put together a swish-looking macropad design, based on an Arduino-compatible WCH CH552G microcontroller — and coming in at just $8 in parts.

"A few months ago, I developed and open source the 4xMacropad, a $3 macropad made using [the] CH552G," Chui explains. "After seeing much of the feedback from the internet, I notice I can better utilize this chip to make a keyboard with more keys. That is why I am trying to make a numpad in order to use 100% [of the] potential of this particular chip."

Chui's original bargain-basement $3 4xMacropad was, as the name suggests, limited to just four keys. While its $8 successor may come in at a little over twice the price, it offers much more than double the functionality: the gadget uses a 4×5 layout with 20 keys — or 17, if you'd rather build it as a number pad with three elongated keys including Enter.

"There are lots of good looking mechanical numpad[s] out there with cool designs," Chui says. "But most of them falls into the 40-50 USD range (for DIY kits). That is why when I am deciding [for] this numpad, my goal is to make it as cheap as possible, while maintain[ing] the good features from the previous builds: Arduino programmable; cheap and easy to make; little to no change in BOM [Bill of Materials] list [from the 4xMacropad."

The resulting design is, as before, built around the WCH CH552G, an eight-bit microcontroller with a single enhanced E8051 processor core running at up to 24MHz. The reason for its popularity in projects like this, aside from its low cost: an integrated USB peripheral, making it a one-chip solution for USB accessories — plus the switches, LEDs, and a few capacitors and resistors, of course.

The design files and source code for what Chui has named the 4x5Macro-Numpad are available on GitHub under the permissive MIT license, with full build instructions published to Instructables.