Accelerometer Sensor

[CocaColaKid]

An accelerometer will just measure the time is takes to go from one speed to another speed, not the distance. It has no way of knowing how far it has traveled unless it is constantly accelerating and decelerating.

[sayzer]

Actually, there are ways of calculating the distance using accelerometer data.

The only important point is that you should not turn the device ON/OFF while it is moving.

1. The user must make sure that the device is first powered up when its speed is zero.
2. Then, you can log the data until it tells you that the device is no longer speeding up.
3. Then you know the formula to calculate the speed with the last data you received. Start a timer here.
a. If the subject hits somewhere, and stops suddenly you should time its speed to understand that it hit something and stopped.
4. Stop the timer when the device tells you that device speed is decelerating.
5. When the device tells you that device is no longer decelerating then
a. the subject is either stopped or
b. the subject speed is constant.

You can use basic math to distinguish between a and b.


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[Acetronics2]

An accelerometer will just measure the time is takes to go from one speed to another speed, not the distance. It has no way of knowing how far it has traveled unless it is constantly accelerating and decelerating.

Hi, KKKid

Not really true ...

if you integrate accel*time, starting from zero ... you will be stopped for integrated result = 0 ...

But, as in real life, there are always calc. roundings and little sensor errors ... you never get a true detection.

The Proof : Model planes Heading Lock Gyros ... Yess !!! The Heading is good ( or considered good ) for a Zero integration sum ...

Alain

[CocaColaKid]

Ok, I stand corrected. You could use one to do the calculations but it would have to work perfect. I talked to an aviation engineer about this and he laughed. It is possible, but the calculations would be nasty. For example, what happens when the elevator is going up or down and some kid jumps in the elevator? Unless the math is done precisely and the event cancels itself out then you'll end up with and error in you distance.

[Acetronics2]

For example, what happens when the elevator is going up or down and some kid jumps in the elevator? Unless the math is done precisely and the event cancels itself out then you'll end up with and error in you distance.

Héhé ... no error due to children nor !

integrating their movements give a precise 0 Sum : they do not fly or pass through the floor !!!

Alain

PS: take care to aviation engineers ... they perfectly know their manuals ... but I already had some surprises about their flight mechanics knowledge ...
Especially for balancing models ... they didn't learn the stab lift effect could be from down to up !!!

Dangerous for a big liner ( can become unstable at low speeds )... but widely used for gliders in contests !!!


re-PS: Talk of inertial guiding to your engineer ... will he still laugh ???

[CocaColaKid]

That is what I meant. Every movement will have to have an opposite in order to zero it out. The problem I see would be making sure that always happens in the math. Making that many readings and trying to get them to zero out in such a short period of time I would imagine would be very difficult.

[Boris]

Hi, I'm developing a localizator with the accelerometer MMA7455L, but it don't works.
Someone used this sensor?
I'm using a PIC16F88.
I'm connected the pin 1,6,7 to 3,6 VDC; the pin 2,5 to GND, the pin 14 to micro's SCL and the pin 13 to micro's SDA. SDA and SCL have two 4,7K pull up resistors. I try to read some register without answer. I try to connect pin 4 to GND, but without effect. Is the device address $1D?
Have you some software example for read and write the registers with I2C Bus? Can you help me?

This is a piece of code:

IND1 CON $1D '%00011101

PAUSE 2000

MAIN:

ADDRESS=$1A
I2CREAD SDA,SCL,IND1,ADDRESS,[TMP]
DEBUG "MODE1 ",BIN8 TMP,13,10
PAUSE 1000

goto main

thank you