Re: gEDA-user: CR2032 with supercap, was Re: [SOT] suggestion for a SMT switch

[Jason <geda@xxxxxxxxxxxxxx>]

andrew whyte wrote:
>  I know that this isn't very sporting, but I honestly can't remember...
> 
>   Rather than spending a long time on worrying about supercaps why not
> stack two coin cells in series and have a little LDO from 6V to 3V3,
> the LDO wouldn't be efficient when your running 100mA, but for 1s that
> wouldn't be much of a problem, the rest of the time your PIC could run
> efficiently.  Better still, you could run the motor straight off the
> batteries (with PWM) so that they droop, but the LDO & PIC isn't
> affected.  Run the LDO at the lowest possible voltage (2.7V) to
> minimise the chance of brown out.
> 
>   There are plenty of tiny LDOs in SOT23-5 footprints etc. if space is
> a problem.  You should really still have bulk capacitance (or at very
> least put the footprints down for it)
> 

I tried stacking coin cells when I first started this whole she-bang. 
The problem I ran into were the physical constraints.  I only have 
enough height above board for a single 2032, or two 2016's.  The 
increase in voltage was good, but the drop in capacity killed me (220mAh 
down to 70 mAh).

thx,

Jason.



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