# Accelerometer and gyroscope

trannh
Hi,

I am an engineering student that needs help using an accelerometer and a gyroscope. I'm not sure where to begin. How can I setup the sensors to output readable data to a computer. Do I use a microcontroller? Do I need to program anything? I am just in need of help. Anything would be greatly appreciated. Thank you

Homework Helper
Staff Emeritus
Depending on your application, you might well need to learn about filtering as well. Kalman filters are widely with navigation sensors. In fact, navigation, particular, getting humans to the Moon and back, was the motivating factor that led to the development of this technique.

So what exactly is your application?

=====

Yech. Accerometers do not sense gravity. Nothing can (directly).

Topher925
The first thing I do before I start anything is find all the necessary datasheets for the components I am working with. What accel and gyro are you using?

Yech. Accerometers do not sense gravity. Nothing can (directly).

Uh, why not? Every accelerometer I have used detects a gravitational field. I can directly detect gravity. I don't understand this statement.

Cyrus
The first thing I do before I start anything is find all the necessary datasheets for the components I am working with. What accel and gyro are you using?

Uh, why not? Every accelerometer I have used detects a gravitational field. I can directly detect gravity. I don't understand this statement.

Accelerometers measure forces, which get converted into accelerations.

Staff Emeritus
Uh, why not? Every accelerometer I have used detects a gravitational field. I can directly detect gravity. I don't understand this statement.
Accelerometers cannot, and nothing can, directly detect gravity.
• Accelerometers would be much less useful for ground-based applications if they could directly detect gravitation. An accelerometer sitting still on the ground measures 1g directed upward precisely because accelerometers cannot sense gravitation. If they sensed gravitation also, they would register 0.034 m/s^2 at the equator, less elsewhere, and this acceleration would point toward the Earth's rotation axis. Accelerometers don't work that way, fortunately. They sense the outward normal force but not the inward gravitational force.

• Spacecraft navigation would be much simpler if accelerometers could directly detect gravitation. Accelerometers on a spacecraft are sensitive to drag, thruster firings, acceleration due to spacecraft rotation, etc., but not gravitation. An accelerometer at the center of gravity of a non-firing, non-rotating spacecraft well outside Earth's atmosphere will register near-zero acceleration (all that's left is solar radiation pressure). Spacecraft navigation systems must instead compute the acceleration due to gravity. This means the onboard software needs to model of Earth's gravity field, and because Earth's gravity field is not spherical, the software need a model of Earth's rotation as well.

• Einstein's theory of general relativity would be false if accelerometers could directly detect gravitation. That they cannot is a direct consequence of the equivalence principle.

Topher925
Accelerometers cannot, and nothing can, directly detect gravity.

Ok, now I understand, had momentary brain lapse. Accelerometers (and nothing for that matter) can directly detect a gravitational field but only the forces that the field generates.

PS: Sorry for hijacking the thread.

trannh
I'm trying to make a system that will allow me to record the acceleration/velocity of the foot during walking, as well as the rotational velocity of the foot. I'm using the MMA7455 3-Axis Accelerometer Module and the LISY300 Gyroscope Module. I'm not sure how and where to connect these sensors to in order to get readable data on a computer. How do I connect the sensors (to a board? What kind?) Also, I'm thinking about using a microcontroller and a transmitter. Would that work?

Perfection
I'm not exactly sure why one would need a gyroscope and an accelerometer. What can you do with a gyro that you can't with an accelerometer?

But basically, you've got modules with SPI buses on them (one has I2C). You take your microcontroller of choice and wire 'em up like this: http://en.wikipedia.org/wiki/File:SPI_three_slaves.svg

Depending on what microcontroller system you're using you might have something with a transmitter on board. Alternatively, you could just wire it to the computer.

Of course, if you're willing to ditch those modules, you could just get yourself a ready made solution.

A fun possibility might be this EZ430-Chronos sports watch development kit put out by TI. It's got an Accelerometer, wireless tranciever, and a microcontroller all in a cute little package!

http://focus.ti.com/docs/toolsw/folders/print/ez430-chronos.html

Last edited:
trannh
So the accelerometer can give me rotational velocity of the foot during walking as well?

I'm still a beginner with wiring. Should I soder the sensor(s) to the board, then the microcontroller, then connect them? I'm just confused on the order of the connections. So i would just need the sensors, the microcontroller, the board, the battery, which would connect to the PC? Also how would I connect it to the computer. Would using the following work?

http://www.parallax.com/Store/Microcontrollers/BASICStampOEM/tabid/135/CategoryID/10/List/0/SortField/0/catpageindex/2/Level/a/ProductID/501/Default.aspx

It seems to have a connection that could connect to a PC.