Thomas Flummer's SAO Digital Multimeter Puts a Functional Piece of Test Equipment on Your Badge

Electronics engineer Thomas Flummer has designed a badge add-on that could really get you out of a jam — delivering, as it does, a functional digital multimeter in a Simple Add-On (SAO) format.

"This is a digital multimeter with an SAO connector on the back, mode selection knob and test lead connections on the front," Flummer explains of his creation, the sensibly-named SAO Digital Multimeter. "Designed mainly as an assistive device during badge development, but also as an exploration of multifaceted engineering, combining electronics and mechanical design to have a relatively compact end product, that also looks right."

The Simple Add-On standard delivers a connector that makes it easy to build accessories for electronic event badges — with most delivering something like an addressable display, speaker, or simple some shiny LEDs. The SAO Digital Multimeter is different: while it does indeed deliver a small OLED display, it's also a fully-functional piece of test equipment.

Hidden inside the 3D-printed housing is a Raspberry Pi RP2040 microcontroller, some flash memory, and a power supply circuit capable of flicking between USB and badge power. A rotary encoder on the front, above two 2mm banana sockets for external probes, allows the meter's various functions to be selected: badge SAO voltage, LED/diode testing, continuity testing, I2C testing, general-purpose input/output (GPIO) testing, and resistance measurement.

"This is of course not the most precise measurement tool," Flummer admits, "but should get the job done for the simple stuff, like testing LEDs or checking a GPIO pin on the SAO connector."

More information is available on Flummer's Hackaday.io project page; KiCad project files and 3D print files are available on the project's GitHub repository under the Creative Commons Attribution-ShareAlike 4.0 International License.