Accelerometer Sensor

[Pesticida]

Hi Skimask,

The Mnimum Value I have is 130 and the Max Value is 167 .
= 3,173 Volt - 2,5 V = 0,673 V ~ +-2g

What You mean what is the Best way to found the Speed and the ~ Distance?

Thanks

Regards Pesti

[skimask]

Hi Skimask,
The Mnimum Value I have is 130 and the Max Value is 167 .
= 3,173 Volt - 2,5 V = 0,673 V ~ +-2g
What You mean what is the Best way to found the Speed and the ~ Distance?
Thanks
Regards Pesti

So you get 130 when?
and you get 167 when?

673mV for 2g worth of acceleration is not a lot to measure or play with.
If you're trying to make a speed/distance sensor, I hope you're reading the part as fast as you possibly can and not just a few times a second.

And in your first post, the math is all wrong...

5 Volt Ref,50 Hz Bandwith with 0.1uF.

At 3v, the output is 174mV/g. At 5v, you should have 290mV/g, with ZERO g at 2.5v
So, first off, you have to set the thing so it's sitting level, sensing nothing, right at 2.5v, and/or trim the output to read 2.5v using an external means.
Turn it 90 degrees one way in the axis you are measuring, the output should drop 290mV (1g), turn it 90 degrees the other way from the original 'idle' position, the output should rise 290mV (1g).

-0.061g*10 Seconds = Speed -0.61 Meters in 10 Seconds
-0.61 * 10 Seconds = Distance 6.1 Meters

All wrong...
1g acceleration = an acceleration of 9.8 meters per second each second
If you measure 1g of acceleration continuously for one second, at the end of that second, your accelerometer will be traveling at 9.8 meters per second, but will have covered only 4.9 meters (assuming a constant rate of acceleration).

Therefore, .061g of acceleration = .5978 meters per second - per second.
At the end of 10 seconds, the speed will be 5.978 meters per second (assuming a constant rate of acceleration), and the object will have moved 2.989 meters (again, assuming a constant rate of acceleration)...

I don't want to say that it's basic math, but if you're playing with PICs, math like this should come easy once you know what to look for.
http://en.wikipedia.org/wiki/Acceleration

[sayzer]

I think our friend Pesti missed an important point that Ski made.

Accelerometer "does not" give you usable data while it is moving at a constant speed.

It gives you usable data while its speed is increasing or decreasing.

[skimask]

I think it might be easier to think of it this way...

You are an accelerometer. You are blind folded sitting in a car. It's completely quite. The car isn't moving.

How can you tell if the car starts moving? You get pushed back in the seat a little bit for little awhile.
How can you tell if the car is speeding up? You get pushed back in the seat for a bit for a little while.
How can you tell if the car is slowing down? You get 'pulled' forward out of the seat a little bit for a little while.
If you don't get pushed back in the seat or 'pulled' forward out of the seat, did the car change speed?

[Pesticida]

HI :-)

Thanks People,

Skimask the Car don't change the Speed.

Thats mean that a Elevator for a little bit is accelerating and then have a costant Speed for a time T.
When is slowing down the acceleration is going in the other direction and the speed is decreasing.

Thats mean that I need a faster Bandwith,I use ADCIN and after that Hserout on my Microcontroller every 50 mS

Is that correct?

[skimask]

For the most part, yes.
Read the ADC as fast as you can, compute the data later if you can, otherwise it'll take away from the time that could be used to capture another sample.

[Pesticida]

Skimask what bandwith should I use ,between 1Hz to 2Khz ?

I use this for the moment:

Main:

ADCIN 0, adval[0]
Pause 1
ADCIN 1, adval[1]
pause 1
hserout ["A",DEC3 Adval[0],"B",DEC3 Adval[1],13,10]
Pause 50
Goto Main

Maybe I can use this

Main:

ADCIN 0, adval[0]
ADCIN 1, adval[1]

hserout ["A",DEC3 Adval[0],"B",DEC3 Adval[1],13,10]
Pause 30
Goto Main

Regards Pesti