This thread of Nick Gammon has me thinking about capacitors, specifically supercaps although the one in his example is a normal one I think.
A 1F supercap like this is less than 20mm diameter.
Could that play a part in your solution?
This thread of Nick Gammon has me thinking about capacitors, specifically supercaps although the one in his example is a normal one I think.
A 1F supercap like this is less than 20mm diameter.
Could that play a part in your solution?