Simple count up timer using a Adafruit Trinket M0 and an HT16K33 7 Segment display. The interrupt_timer.ino version is the most up to date and the only version that yields accurate time. It starts counting by seconds for the first 10 minutes and then switches to hours:minutes. This works good as a pit timer if the device is on batter backup and the driver remembers to reset the clock on pit-in.
This is just a simple implementation of a countup timer that starts at 0 and counts up, displaying hours and minutes since the device first powered on. It's set to start flashing the time at the 1 hour 50 minute mark as this was setup for a use case where there was a 2 hour limit on an activity.
The initial implementation was done with CircuitPython and is in the circuitpython directory.
Simply placing the contents of that directory on a Trinket M0 wired to a HT16K33 display should work
as expected. I noticed a little drift with the time, about 1 minute per hour, so I intend to build an
Arduino sketch for the device to see if I get different behavior.
There are two Arduino sketchs, first was a straight forward approach using the 'millis()' function and more or less replicating the circuitpython code. This exhibited the same clock drift as with circuitpython. The interrupt_timer.ino version uses an interupt on one of the devices timers to count seconds since startup. This approach appears to yield much better time accuracy, at least enough to have miminal error for the duration I'm trying to measure.