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A Homemade Acceleration meter

A Homemade Acceleration meter

Basically the AccelR8 is a device for measuring acceleration. It can measure +/- 2 g. As it contains a microprocessor, it an also measure time. This opens up some interesting possibilities. If we have the acceleration and the time, we can find speed (V), as V = a * t.
Also, we can find distance (D) as D = 0.5 * a * t * t. If we now the mass of the object we are moving, we can also find the force (F) applied, as F = m * a. 
And finally, from this we can find the power (P) from P = F * V.

So, after this Physics 101 refresher, what does all this mean ?

It means that you can just enter the weight of your car into the AccelR8, find a straight and level piece of road, go Bleifuss on the accelerator, and AcceR8 will tell you :

Acceleration 0-100 km/t (0-60 mph),Braking distance 100-0 (60-0), and Maximum Horsepower, as well as a number of other interesting things. If you’re not careful enough, a cop may tell you a number of unrelated uninteresting things ! 

The operation and mode is controlled by a single pushbutton on the front. Calibration and value settings are made by simply tilting the device and using earth-gravity to scroll the values.

The schematic show that the AccelR8 only uses 3 IC’s. An AVR 8515 microcontroller do the calculation work and controls the other circuits. An MAX603 controls voltage and power-on/power-off. And the chip that makes it all possible, the ADXL202 from Analog Devices measures the acceleration.

This chip is a small wonder. It uses a tiny micromachined polysilicon structure on the silicon wafer. The structure is part of a capacitor, so deflection of the structure (by acceleration) can be measured.
The ADXL202 can measure acceleration in two axes, and if you have a Microsoft Freestyle Gamepad, you already have an ADXL202 !

In this case, we only use one of the axes, and the ADXL202 outputs this data as a variable duty-cycle squarewave. The 8515 calculates the acceleration by measuring the pulsewidth/period relationship. The acceleration is then used in further calculations, and the resulting data is show on the display.

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