This is a fun project. Unfortunately, it takes some time to develop the code, so this is a work in progress and here i’ll just present the project so far.
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
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 AcceR8 in it’s cage.
AccelR8 innards. Click to see large image.
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.
Schematic is available for download below. Unfortunatly the source code is not available yet.
Copyright 2006 [url=http://www.myplace.nu/avr/]Jesper Hansen[/url]