If you’re ever in a posh car or on an expensive motorbike, you’ll sometimes notice that when you turn the ignition on, the speedo and rev counter dials do a quick self-calibration, moving their indicator needle all the way round the dial and back to zero again.
Instead of using a traditional meter mechanism (a simple coil and magnet), they use a tiny computer-controlled stepper motor. Here’s one removed from a dial:
The metal shaft sticking out used to have a little plastic indicator needle on the end. Inside, they’re more like a watch mechanism than a traditional stepper motor:
The tiny black cog in the middle is magnetic, and sits in the round gap in the metal frame just to its left.
Power up the two coils in the right sequence, and it drives the tiny cog round, in turn moving the other cogs which move the indicator needle.
These are more traditional stepper motors, though still very tiny:
I dug them out of a tiny camcorder. The shorter one controlled the focussing lens, while the longer one controlled the zoom. The little chip on the left is an Atmega168 – similar to the chip in an Arduino. With luck the chip’ll have enough power to drive the motors directly. Not sure yet what I’m gonna get the motors to do, exactly, but whatever it is it’ll be tiny and very cool. Yeah.
I tried some of these tiny steppers on an Arduino:
You can indeed drive them directly, I need to add some current limiting though. However I’ve heard a better method may be to use PWM.