Joey Castillo Goes Straight Edge, with an Oddly Specific Ruler Powered by a Microchip SAM L22

Joey Castillo, of Oddly Specific Objects fame, has completed a "rite of passage" in the world of electronics: building a functional PCB ruler, the software for which is planned to include unit conversion, financial calculations, an "electrical cheat sheet," and more.

"It feels like a rite of passage to make a PCB ruler, but I wonder if this is actually a product," Castillo writes of his latest creation. "This ruler has a [Microchip] SAM L22 [microcontroller] just like Sensor Watch, with a 16-button touch matrix and an Oddly Specific LCD that can display five digits and some indicators. Plus five GPIOs [General Purpose Input/Outputs] and I2C pins exposed on an edge connector. I made this to throw in my soldering go-bag, but I think it could have broader appeal, depending on the software I write for it…"

Castillo's latest object is, of course, a functional ruler: inches are measured out along one side, with centimeters along the other. It's also a fully-functional standalone microcontroller board, featuring USB power and data to one end of the board and the "Straight Edge Connector" to the other breaking out three analog inputs and two digital inputs/outputs, an I2C bus with on-board 3.3k pull-up resistors, 3.3V regulated power and unregulated 4-5V from USB or an optional battery.

The display, meanwhile, is culled from excess stock of a custom LCD panel Castillo designed and had manufactured in quantity for earlier projects, based on those you would find in an alarm clock and with support for five numerical digits and a selection of indicator icons. This will be driven, Castillo explains, by as-yet unfinalized software.

"My thoughts right now are unit conversions, financial calculations (margin/markup), hex/decimal conversion, an electrical cheat sheet (Ohm's Law, RC calculations) and of course time and date stuff (probably with an RTC on the accessory board connector)," Castillo writes of said software. "I bet I could also do an add-on with an LED and phototransistor like the Beancounter [device for counting taped surface-mount components], to do parts inventory on the go."

More information on the project is available on Castillo's Mastodon post; no decision has been made as to whether the prototype will progress to a production run of an Oddly Specific Object for sale in the maker's store.