FYI, if you want to start a process to run on startup and continue running, then you can add it to /etc/rc.local, but that'll keep rc.local running until your process finishes (never, possibly)
Instead, you can use start-stop-daemon:
start-stop-daemon -S -b -x /root/project/project-script
You'll need to make sure your script is executable, too. The -b puts the process in the background so it won't hold up execution of the rest of rc.local.
Duh. Solved the problem... I had a script in /etc/init.d that wasn't backgrounding properly, so the system wasn't actually booted all the way; as a result, the button wasn't working. Fixed that script, and the button now works as expected.
Anyway, I confirmed the script in /etc/rc.button/reset does work, and you can replace the reboot line with whatever you want. I hope that helps someone.
I have a BME280 -- very similar; it includes temperature and humidity in the same package; they might actually be the same product, just with one part zapped -- and it's reporting fine without spikes. I'm doing the same kind of graphing job, I think.
I'm feeding the Expansion Dock with 5V from a good power supply with a barrel connector, rather than a USB charger. A power supply and a charger are quite different, though: chargers tend not to provide good power, especially third-party/no-names/knockoffs. I doubt the Expansion Dock will stabilize that well enough. I'd suggest getting hold of an authentic Apple USB charger temporarily just to see if it makes a difference, as I've found them to be of much better (smoother) electrical quality than others.
Hope that helps!
Re: Programming on-board reset button
I've identified the reset button logic is in /etc/rc.button/reset:
...
if [ "$SEEN" -lt 1 ]
then
echo "REBOOT" > /dev/console
sync
reboot
elif [ "$SEEN" -gt 5 ]
then
echo "FACTORY RESET" > /dev/console
jffs2reset -y && reboot &
fi
...
which Google tells me is run by procd. Customising this script would presumably alter the behaviour of the button, allowing it to be used in software, albeit probably not as a standard GPIO (as procd will still hold that port open)
cat /sys/kernel/debug/gpio also tells me that gpio-11 (reset) is an input, currently lo. If I press the button, this changes to hi, as expected.
However, on mine, it doesn't seem to lead to a reset, and I can't see a console message either. I wonder if this still works since I upgraded to firmware 0.1.4 (b330)... Any idea?
As I've invested some effort in getting this unit the way I want it, I'm loathe to try pressing it for more than five seconds to see if that works.