Useful Smart Phone App

Me neighbor works for the county occasionally building bridges and stuff. He showed me this smart phne app that let's you use your phone as a level. You can you use it any which way: lay it down flat, on edge, or standing up, and it will show you just how flat or level or plumb things are. I was doubly shocked when I saw this. One, because it was something useful you can do with a smart phone, and two, I had been looking for something like this a long time ago and couldn't figure out how to do it.

Back when I used to ride my bicycle I thought it would be cool if there was some kind of gadget that could tell you how steep, or flat, the road you were riding on was. Sometimes you are sailing along and you think the road is flat, which makes you think that you are pretty tough, but what if it is actually an imperceptible downgrade? That would take some starch out of your sails. Or you are grinding along on some road that looks flat, but geez, this is a lot of work. Maybe you are actually going uphill. And how about when you come to an actual hill? Something like this could tell you just how steep it is. Anyway, I thought a gadget that could tell you this would be pretty cool, but I could never figure out how it could be done.

I was talking to Jack about this and our conclusion is that this is an outgrowth of the freefall sensors that go into laptop computers to protect the hard drive in case you drop it. Freefall sensors are actually 3-D accelerometers. When your laptop is sitting on the table, it is subject to the force of gravity, which as we all know (don't we?) is indistinguishable from acceleration, which is really weird when you think about it. Basically we have a lever sticking out horizontally and supported at one end. The force of gravity is pulling on our lever, and since one end is unsupported, it is causing it to bend. A strain gauge measures how much it is bending.

When you drop your laptop, the force of gravity is no longer bending the lever, the strain gauge registers the absense of strain, which tells the laptop's little computer brain that we are falling (or we are in orbit). This prompts the computer to retract the heads on the hard disk so that when we hit floor the heads are held securely and away from the disk surface so they don't collide and get all eff-ed up. All this takes milliseconds, a fraction of the time it takes the laptop to fall to the floor. Well, if you drop it from a table. If you drop it from a lower height, like a couple of inches, you might be able to defeat this protection mechanism and screw up your hard disk.

Anyway, some whiz kids came up with the accelerometers, and somebody thought it would be a good idea to include it in a smart phone. It's just one more component, it probably costs less than a buck, it might turn out to be handy, and who knows? Maybe there will be hard drives in smart phones one of these days. And presto, here we are with a really useful little engine.

The device at the bottom left with the C-shaped wings is an accelerometer

This is the only picture I found of an accelerometer, and I don't even know whether it is typical or not.

Update January 2020 replaced missing image.