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Old 05-12-2013, 05:57 AM   #17 (permalink)
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I really like Old Tele man's pendulum accelerometer. It's so simple and easy I think you have to try it and see if it will do what you want.

You could also home build the fluid filled inclinometer. It would be a loop (to prevent spills - use an irrigation pipe joiner to form the loop) of clear plastic tube, part filled with water, fastened to a board using U staples with an angle scale marked on it. Food colouring in the water would make it easier to read.

Did you find Accelmeter and Clinometer iPhone apps. which amount to the same thing as the physical pendulum and inclinometer?

Maybe you can find a used first generation G-Tech cheaply.

Could you find a digital protractor/inclinometer cheaply. (New I think they start around $50.)

A problem with each of those is they don't separate vehicle acceleration from the change in acceleration due to the slope. That would be OK if you could hold a steady speed on the slopes. Maybe you could 'map' the slopes of roads you regularly travel on by stopping or ensuring that you were travelling at a steady speed when taking the measurement.

To use an Arduino:

Arduino - ADXL3xx

might get you started on how to measure the accelerations.

The adafruit ADXL335 3-axis board is U$15.

The display could be 2 or 3, 7-segment LED's, driven by a 4511 binary coded decimal to 7-segment driver and multiplexed. There's any number of tut's on how to do that. Three displays, the 4511, 3 transistors and the current limiting resistors would be ~U$15. (You might prefer to use a 16x2 LCD display instead if you intend to use the Arduino for other things as well.)

A prototype shield board for maybe $5 and some wire plus the Arduino @ ~$40. Under $100 for the whole thing and you will still be able to use the Arduino for the grill block as well. Too expensive?

You will have to do some 3D trig. in the code/sketch to convert the outputs from the sensor into something sensible to you on the display. You will also have to read the vehicle speed sensor (I'll assume that your car does have one - it should), convert the rate of change in that into a linear acceleration, and subtract or add that to the 3-axis sensor acceleration. That won't require extra hardware to do though.

It still doesn't address lateral acceleration. There are the gyro. sensors that might be used to remove that due to turning - the car will be yawing if there is lateral acceleration - but it gets more complex with it. A lateral slope will still be a problem.

If it helps, the maximum acceleration, slope plus change in vehicle speed, that I saw on a G-Tech when I was checking typical acceleration, some time ago, during 'normal' driving, was a little over 0.30g. That means you will probably need the 3 digits to get something meaningful in terms of slope i.e. to display the 'g' reading as something like (.)300(g). 7% (^) would read 070. The decimal point being implied.
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