This Low-Cost Compact Carrier Board Turns a Seeed XIAO SAMD21 Into an 18V Six-Channel Voltmeter
Using voltage dividers to boost the input range, this clever carrier board makes for a handy multi-channel diagnostic tool.
Pseudonymous maker "gokux" has designed a carrier board that turns a Seeed Studio XIAO SAMD21 board into a six-channel 0-18V voltmeter with onboard OLED display — powered from a USB Type-C connector.
"Some special applications often have to measure the voltage from several parts at the same time," gokux explains of the reason for a multi-channel device for reading differing voltages. "For example electronics repair, scientific, and experimental purposes. If you're building a battery pack it can also show the voltage of each cell simultaneously."
Rather than picking something up off-the-shelf, though, gokux decided to build a voltmeter of their own — taking, as its base, the compact Seeed Studio XIAO SAMD21 development board. To this, gokux added a 0.91" 128×32 OLED, a handful of resistors, and headers for ease of connecting to the device on test, all mounted in a custom-designed carrier board.
"[The] XIAO only can measure the voltage up to 3.3V," gokux explains of the resistors' purpose. "More than that will damage the MCU [Microcontroller Unit], so we need to use a voltage divider for that. As the name suggests, a voltage divider will help us to divide higher voltage into smaller voltage which can be measured using [the] XIAO. We are using 100k and 22k resistors to build our voltage divider; with this we can measure [from] 0V to 18V. More than this limit will fry your MCU."
The full project write-up is on Hackster, with schematics and Gerbers for those who want to build their own.