Sorry, I've read the thread properly now. You have a bit of a problem, most supercaps will be larger than a second coin cell. You could charge a capacitor through a p-channel mosfet and resistor, turn this off from the pic, and release the power in the capacitor onto your vibration motor from an n-channel mosfet. For a small system like this you should be able to use the body diode of the mosfet to remove back EMFs.
The challenge will be to charge the Cap, as fast as possible without browning out the coin cell, this shouldn't be too hard, it is the potential divider between the cell's internal resistance and the series resistor | P-channel 'on-resistance'. That will give you an idea of worst case voltage droop. Perhaps with some fiddling you could find a resonant frequency of the vibration motor and get the system to pulse repeatedly... anyone? I've seen something like this done in the Beam Photopopper [1] (circuit at[2]). By Philosophy, they aren't worried about brown outs, but they are running a pager motor off of a 4700uF capacitor at 0.5V, this makes me think that you *might* get away with something like this... Do some checking/calculations before you start laying out a board though. Maybe just charging a cap up to 2.7V, and shorting the terminals with the motor would tell you how big the cap has to be to get the motor moving experimentally. [1] http://www.solarbotics.com/products/k_pp (circuit diagram in the 'resources' tab) [2] http://www.solarbotics.com/assets/documentation/solarbotics_photopopper_kit_may032007.pdf N.B. All of this info is supplied without warranty, please remember all the usual safety stuff. I am assuming that you are a skilled professional capable of doing your own risk assessment. -- ╒═════════════════════════════════════════════╕ Andrew Whyte MEng CEng paramita ltd ╘═════════════════════════════════════════════╛ _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user