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Anybody interested in a cheap IMU?


#1

Terrorgen and I were going to make a few IMUs roughly based on the Sparkfun 9DoF Stick: http://www.sparkfun.com/products/10321

Our board would be close to the same as the Sparkfun board, except that we are planning to replace the old HMC5843 for the far less expensive, higher resolution, smaller HMC5883L.

We are also replacing the 0402 passive components in the reference design for 0603 for ease of assembly.

As it is set, Terrorgen will do the board assembly, but we might do something different depending on how many people want in.

We estimate each IMU will be between $30 and $40.

Anybody else want to get in on this?

This is a cross post from: http://forums.netduino.com/index.php?/topic/1277-anybody-interested-in-a-cheap-imu/


#2

This IMU really has a lot of potential. Since it is not tied to any microcontrollers (like other 6-9DoFs found in Sparkfun) users are not forced to program in the specific microcontroller that it comes with. Grab a random microcontroller in your parts bin and program it as you wish! (As long as it has i2c pins)

The only thing I am not happy with it is, it is wayyyy overpriced.

Furthermore I wrote the driver for this IMU and posted it on Fezzers. So if you want to interface this IMU in .NET it is ready for you.


#3

I will also be making a full netmf library for cross compensation, DCM, etc.


#4

$24 gyro
$5 accelerometer
$20 magnometer
$1 regulator

$50 in parts

So how is this going to be done for $30? or $40?

Board $10 (you are doing 10 boards, right?)
Assembly will cost about $50 each for low volume! Hand soldering on these lead-less chips may not be a good option.

Unless you are making hundreds/thousands, a $100 to sparkfun may not be a bad idea :frowning:


#5

I’m inclined to agree with Gus here. This does seem to be a rather ambitious price point.

$10/board seems optimistic with tooling fees included…

You’d need at the very least for hand assembly a stencil and placement jig - another $50+ and still may get a 10-20% failure rate. Without a placement jig (basically another pcb or laser cut perspex with apertures for the components to be dropped into) you’d be looking at 20-40% failure rate and 5-10 mins assembly per board. This assumes you already have solder paste, which could be another $50-60 for a tub.

LQFP/QFN are pretty painful to deal with, especially with the smaller (12-20pin) packages. These are very very tiny and need to be exactly positioned. Hot air reflow is difficult on these parts because they are so small you need almost no airflow so as not to move them before they float. If they do move slightly, the 0.3-0.5mm pitch pins can be shorted at even a 2 degrees of rotation or 0.2mm of movement laterally.

Sorry, but i’ve done a lot of these for prototypes and know that you can throw away half the boards when using just a stencil and hand placement - or 1/5-1/3rd of the boards when doing jigged placement.
By all means, go ahead and do it - but first make up a spreadsheet with all the costs factored it so you don’t cut yourself short.


#6

“Board $10 (you are doing 10 boards, right?)”

Who is doing PCBs for 10 bucks a board? tia


#7

Anyone use this type of three-axis accelerometer (see link). X,Y,Z outputs are just centered at half the voltage of the 3v3 source.

If you just need accelerometer, such as a segway type thing, it seems a lot easier to read voltage levels then a bunch of I2C. Was wondering if some have used.


#8

For my own board (Panda Motors, PCB size the same as Panda), I got a $20 price per board for 100 boards assembled and fully functionnal, ENIG finish. Without all taxes, of course. If I add taxes (customs, shipping, and so on), each board is near $25 excluding VAT.

But it was made with cheap components : the more expensive being the DRV8821 near $5. You have “expensive” parts on your board.

Also, don’t forget to include shipping/handling in your price :wink:

But, like MarkH said, go for it ! If it doesn’t cost you much money, then it’s a very exciting project ! :hand:


#9

i underestimated the cost… maybe i shall mark up to about $60 - $70.