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?

up vote 3 down vote accepted

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.

  • Thats a really great idea Theran. The status would change 4 times a day (maximum). I would worry about the reliability of the mechanism though. Im new to electronics are there specific low power motors that you had in mind? – aaronfarr Feb 20 '11 at 4:31
  • what a neat e-ink like idea! – Dave Feb 20 '11 at 5:41
  • @Dave that's a nice idea. Similar to what's in this device eink.com/customer_showcase_jumpdrive.html and here's the source eink.com/display_products_surf.html – kenny Feb 21 '11 at 22:48
  • Using a with a somewhat off-balance color wheel might work, but getting it to function reliably may be difficult. The idea would be to have the wheel (attached to the second hand) enough off-balance that when it is in a certain position, short pulses will be unable to drive it, but longer pulses will still work. The indicator couldn't update very fast (perhaps a minute if you want to run to the 'sticking' point and then run 270 degrees past it) but you might be able to get workable open-loop operation. – supercat Apr 25 '11 at 14:46
  • The best motor would be a stepper motor. You can move it in "steps." Each step is equivalent to a certain number of degrees, so you can accurately set it to a certain position without a sensor. A low power one like you would need would be cheap to buy and have a cheap driver circuit. Many tutorials online. And to save money you can turn off the motor completely on certain drivers to save energy, but you can manually turn it though. Maybe some plexiglass or glass? This is the kind of motor that turns the speedometer needle on the car... but I don't think it turns off except when car off. – Anonymous Penguin Aug 12 '13 at 0:05

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.

  • Thank you so much for mentioning these, as I was aware they might exist. I actually found a supplier called AlphaZeta that specializes in them, and they sell them individually and fabricate boards of them. I'm working on a sensor which spends most of its time in idle mode and wakes up only to run tests/transmit. Turning on a low-battery indicator like these is absolutely perfect, as the indicator will remain after it dies. – Aaron3468 Jul 6 '16 at 8:22

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.

  • This is a good idea as well. The challenge is the size as well. The device is about 8mm in height. Any other types of micro-actuators you can think of? – aaronfarr Apr 26 '11 at 19:40

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