The project I am working on requires a color indicator which shows the current state (either red, green, or yellow).
Ideally the indicator would have a large surface area so you can quickly glance at the device and determine the state. 2" x 2" would be nice.
The device is battery powered and would ideally be able to operate for months at a time without recharging.
What would be the best solution to use for this kind of application?
How often does the indicator need to change? If it's only occasionally, then you could place color swatches on a rotor or scroll mechanism and move it mechanically to different positions. The power consumption while not changing would be zero, but it'd be considerable while changing.
One option for the motor/mechanism would be to hack an inexpensive clock movement to be controlled by your project rather than the quartz oscillator it comes with, and stick a disc with your color swatches on in place of the second hand. You can often buy them in craft stores for about $5 US.
Most often found in arrays, flip-disk (or flip-dot) indicators only use power while changing. Finding single dot units may be difficult, though if you're just making a 1-off prototype, you may be able to fabricate your own.
Alternatively, you could use an LCD with a colored reflector you could have either black or the color showing (you may be able to have additional colors besides black). If you want more than two states, you could flash the LCD.
If you want red, green, yellow, and black, you could perhaps get a set of automotive door-lock actuators, and mount them at right angles to each other. Have a yellow square that's always visible, and have the actuators slide red and green filters to either cover or uncover the square (both filters uncovering the square would yield yellow; red and green both covering would yield black; one or the other alone would yield that color). Automotive door-lock actuators are designed to operate off twelve volts, but they would probably work acceptably at lower voltages; they would simply take longer to switch colors.
