Based on the new requirements, I think that a microcontroller is justifiable. I have no doubt that this could still be done without one, but I like microcontrollers, and that's where my experience lies. I plan to use one of the small AVR uCs which are under $1 in quantity.
The device will now have to have both a bi-color LED and a single button. This single button will have to both toggle the state of the LED and allow for dimming. I think that this calls for a UI prototype to see how well this works.
As a side note, I'd much prefer a lit button, but all that I can find are prohibitively expensive.
This is how the button and LED should interact:
- While in the normal (voltage good) state, pushing the button should toggle the green LED on and off.
- While in the low voltage state, pushing the button should toggle between flashing orange and solid orange.
- In any state, holding the button down for a few seconds should start dimming the LED. When the button in released, the LED will maintain this brightness.
- If a low voltage state occurs, the LED should always go to the flashing orange mode (as opposed to solid orange) in order to catch the attention of the operator.
LVW UI Prototype from James Wilkins on Vimeo.
Sorry for the poor video quality. My camera just died on me today, so I had to resort to a web cam for recording the video. It was either that or a cell phone, and the cell phone would have been worse.
I think that this will work. Of course, I'll have to run it past some actual users to see if it proves too confusing.