teensy-clock | A digital clock based on Teensy 3.2 and Rust

Here are the parts I ended up using:.
A Teensy 3.2 microcontroller
A USB power supply and micro-USB cable from an old phone
A SparkFun DeadOn RTC (breakout board for DS3234 chip).
A CR1220 coin-cell battery to keep the RTC (“real-time clock”) running when USB power is off.
An Adafruit 0.56" 7-Segment LED Backpack. It deals with multiplexing and providing constant current (not voltage) to…
A red (not blue) 4-digit 7-segment LED display that came with its controller “backpack”.
A couple 4.7 kΩ resistors because for some reason the Teensy’s internal pull-up resistors don’t work for I²C.
A bit of foam for insulation, cut from the packaging of a computer GPU. (GPU not required for this clock.)
“Jumper lead” wires. They’re designed for use with a breadboard, but are still very convenient for this: the come insulated, in various lengths, with pre-stripped ends, and with solid (not stranded) core so that they keep their shape after bending. Once soldered they provide fairly good mechanical connection, which means this project doesn’t need a “main” board since the whole thing is rather light.