9dof imu

i am starting a new topic because i am really unsure of some of the details of using this device and wanted some feedback from some of the more experienced experts before i waste a bunch of time trying ideas that just wont work.

i bought the 9dof IMU board from sparkfun.com ($124):

if you arent sure what this device can do watch this video from youtube:
[url]Sparkfun IMU Razor 9DOF AHRS code - YouTube

anyways i started with the usb breakout board so that i could attach it to a computer and look at the data is was showing. wiring into the breakout board is very straight forward and using it is simple as opening teraterm and setting it on the right com port (and setting it on english, its a little gotcha). in teraterm it give you the choice of which data you want to see (accel, compass, gyro, etc) and then displays that stream in teraterm.

my question to the experts is what would be the best way to wire this into the fez domino? do i just need the power (3.3v and gnd) and then the tx and rx wired to pins that are set as UART tx and rx pins? is there a better way? i am only guessing here. my electronics skills arent as good as my programming skills, ha. any help is certainly appreciated.

here is how i wired the 9DOF IMU to the breakout board for those who feel like trying this out:

That is an expensive board! If it is serial then you just connect it to one of the serial ports. It should be TTL so direct wires would work fine.

Chris has a forum post and drivers for it. It in this thread some where http://www.tinyclr.com/forum/1/505/

Tx to Rx
Rx to Tx

i dont want to use the breakout board, i want to just want to connect the IMU directly to the domino and was looking for advice on the best way to do it. can i just wire the tx and rx on the IMU to the com in and com out on the domino? if i did that could i just use the simple UART for each way (ie. to send the “1” in the same way that i do over teraterm)?

Exactly as Gus said. Tx to RX and RX to TX, GND to GND, 3.3V to 3.3V. See the above link for my drivers.

Also I see that you have an FTDI USB to serial attached to your board. If you like tou can connect it directly as it is to FEZ Domino’s USB Host.

FEZ Domino supports a driver for USB FTDI. :wink:

Yeah, you can do as Joe said, too.

I’d recommend just connecting it straight to the FEZ over serial.

I’d connect it straight to serial - desolder those jumpers,solder in some headers and then move on. Right now you’ve eliminated any flexibility with hardwiring it.

out of curiousity as i am currently working on a imu unit design, what is the benefit of having the triple axis magnometer in the system. i understand the need for complimenting triple axis accelerometers with gyros, to give a 6 axis imu, and i can maybe see the benefit of adding a single axis magnometer with tilt compensation for absolute heading, but triple axis magnometers i just dont get it.

i`ll be making a project page real soon for this project :smiley: ,my current thinking is uzbizi144, tripleaxis gyro, triple axis accelerometer, baromic sensor [all on i2c bus], gps[ttl uart], plus wireless link, currently undecided on magnometers thou. all mounted on a custom pcb which will eventually mount on my … :smiley: :smiley: :smiley: :smiley: :smiley: tba later :o

You need a triple axis compass to solve for an orientation dependent heading.

NUBIARN: i liked the potential of the additional sensors, but didnt need it, it is overkill but i am still doing research into what i will be using.

Chris: can you send me more of a direct link to your drivers? i am having a little trouble finding it in the 37 pages of comments on that post, ha

i will be removing the additional FTDI, i just had that on to do testing on the board itself. i am still kind of a noob when it comes to wiring of electronics and i knew having the FTDI would mean i could test the board without figuring how to connect it to the FEZ first (since i couldnt find docs on that).

so i should be able to just wire the tx to com in and the rx to com out (with 3.3 and gnd of course) and open a UART for each direction?

See: http://files.chrisseto.com/4xa

Chris: thanks again for that driver file but i have some questions:

  1. in teraterm i am connecting at 38400 and in your driver file you are connecting at 57600, why is there a difference?
  2. in teraterm you must make a selection to which data (accel, gyro, mag) you want to be reading by sending 1-3, how are you escaping having to do this?
  3. (maybe noob question) what are the pde files for in your link?

NUBIARN: i think you need at least a 2-axis magnetometer to give you heading because heading in degrees is something like arctangent(x/y) where x and y are the values from 2 of your magnetometers (at right angles from each other), i think the 3rd magnetometer gives you tilt compensation? someone please correct me if i am wrong, but that was my understanding

that would make sense, true magnetic heading irrespective of attitude vector, umm guess i`ll be adding one then

Yes the 3rd axis gives allows you to partially compensate for tilt.