ADXL202 how to convert gravities to mph?

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1

Anybody know how to convert gravites from the ADXL202 in MPH. Code would help!

Thanks in advance…

2

Well there’s some inherent problems with your question:

The ADXL output ‘gravities’ - or more accurately accelerations. You are wanting miles per hour - or velocity. To get velocity from acceleration, whip out your old physics books. You’ll have to integrate accel once to velocity. Integrate again and you’ll have distance.

Integrating (roughly speaking) with a PIC is not too difficult. You’ll need to check the ADXL reading multiple times a second (100hz should do) and record the gravity reading (units are m/s^2 right?).

1G = 9.81m/s^2

so for every reading you take multiply by the slice of time. For example, let’s say the ADXL is reporting .01G at a specific point in time:

.01G * 100Hz = .01 * (9.81m/s^2) * 1s/100 (this is 100 hz)

delta v (change in velocity) = 0.000981m/s

This is your change in velocity. You’ve just increased speed a bit. Add this number to an overall velocity variable over time.

There are tons of problems associated with using 8-bit micros to do floating point math and big ugly numbers that I won’t go into but it can be done. Also, the ADXL has a tendancy to have reading shifts due to temperature changes. These small changes get magnified by integration.

It’s a sticky situation,

-Nathan

3

Thanks for the infor about how to convert accelerations. I looked at the Firmware v2.1 source code and was wondering if the source for Delay.c and soft232.c are available for download?

Thanks for all your help…

4

Most likely not, as they are probably libraries for the C compiler they used for the project, and hence belong to the compiler company, not Sparkfun

5

I too am looking for soft232.c and delay.c so that I can further develop the SerAccel v3.

What compiler do these come with?

Cheers,

Steve