Originally Posted by
dwoloz
Well thats an interesting note. I briefly considered this as a possibility but never tested it! I will give it a try. If thats true then this whole thing is much simpler than I imagined
The unit memorizes last selected mode just as long as there is some voltage left. Usually there is a capacitor in the unit so this really works but you have to use a diode in the power line to keep the capacitor from discharging.
To make it 100% reliable it would be better to use one AAA cell as a back-up. If you replaced the second cell by a 1N4148 diode, the voltage would be under 1V and no current would be drawn from the cell. Then the last selected mode will be memorized forever, at least I hope it should work this way.
It's a good idea to power it by a DC-DC converter. The cheapest IC I know for that use is the good old MC34063 used in car CL adaptors for cell-phones. It's very suitable. You can even use the 12V CL adaptor as it is only with some output voltage adjustment done.
With a 3-pin regulator you woud have wasted 3/4 of the input power. Instead of that you could use 4 Superflashes in series with the some power consumption!