Accelerometers

Sometimes our biases and perceptions tend to lead us astray. For example, the common association for 'acceleration' is the feeling of being pressed back into your seat as the plane takes off from the ground, or when you stomp on the gas pedal. As a result, when we consider applying technology to solve a particular problem, we almost automatically relegate accelerometers to problems that require the need to measure dynamic acceleration. The idea that they might be useful in tackling other challenges doesn't naturally occur to us. It's obvious that an accelerometer could be put to practical use as a part of an airplane autopilot, or a race car. It's not so obvious that it could provide any useful benefit to something like a cell phone.

But... How about a cell phone digital camera display that senses when you rotate it from vertical to horizontal, and automatically rotates the picture? Something like this-

That's exactly what the engineers at Mitsubishi figured out and built into the V401D cell phone for Vodafone. Rotate the camera and the photo turns to match so that it is always displayed in the right orientation. They used a thermal accelerometer, which at first pass sounds like a non-intuitive approach. After all, what does temperature have to do with acceleration and spatial orientation?

The link between temperature, acceleration, and spatial orientation that eventually lead to the V401D design is based on the Memsic dual axis accelerometer. The inside of the Memsic device contains a liquid with a small bubble in suspension. The bubble is heated and thermopiles around the bubble measure its temperature. When the device moves the bubble moves and the thermopiles pick up the change in temperature. Of course there's a lot of conversion that takes place within the device, like converting the temperature change into a corresponding acceleration value, and temperature compensation.

For hobby robot experimentation, Parallax has packaged one of the Memsic accelerometers and has quite a bit of useful information on how to apply it. They also have detailed application writeup in PDF format that was done for the Nuts and Volts series.

The V401D design really opened my eyes to the fact that they can be applied to more static applications, like tilt angles for a walking robot, or perhaps a Legway clone. Steve Hassenplug, the Legway designer, seemed to think that a Legway couldn't be designed using an accelerometer, but after playing around with a V401D for a while, I'm not convinced that he is right.

It's also fun to contemplate what other neat goodies could be hacked together using this technology. How about a robot Weeble, as in "Weebles wobble, but they don't fall down."? Or a mystery box that always manages to right itself no matter how you set it down, Or ....

If I have the chance, I'm going to pick up one of the Memsic devices and do some experimentation.

You might also enjoy:

  1. Getting My Robot Under Control
  2. Which Way Do We Go, Which Way Do We Go…
  3. Getting My Robot Under Control – Part 2
  4. Somethings Never Change – 555 Timer IC
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