Now, I KNOW this is bouncing around their heads already.
Combine an Analog ADXL330, the new Ivensense gyro and (unless Invensense has another gyro, love that noise rating) a 300 deg/s Analog gyro. Add a pad option would be a “high G” pad ( or enough for 1-3 axes, but only Freescale makes a high G Z) for those who like their IMU’s in rockets :). Now, there will need to be 5V interfacing for the Analog gyro, but they’ve done it before with the Freescale accelerometer.
For those who haven’t grasped this idea yet, this would be a single board IMU without ANY riser boards. None at all. Going with one riser board would allow another Invesense gyro to be used for 3 axis 500 deg/s and low noise, but it loses the core elegence. While I know Sparkfun will toss on Bluetooth, my personal wants mean that I’m going to be building my own, basing it around a CAN equipped PIC or dsPIC.
I do figure this will be around $200 (dunno if that price includes Bluetooth). If this is too fast, it should be simple for Sparkfun to swap in a IDG-1000 with a lower max rate.
Now, back to designing the low cost accelerometer-only IMU (may not be exactly accurate, though!)
analog devices will be coming out with a tri axial gyro at some point, it is still in developement now, the Invensense has very low noise though, I wonder if that’s a true spec. One thing I don’t like about the Invensense gyros, they have no build in temperature sensor, all these gyros are very temperature sensitive and having a temperature sensor directly on the die is the best way to go (like the analog devices parts)
I don’t know. Unless they have an integrated temperature compensation function, I’ll have to order one eventually. The datasheet is rather sparse currently.
it definitely doesn’t have any internal temperature compensation, looking at the datasheet it’s output sensitivity is 2mV/deg/s, the datasheet also indicates the zero rate output over temperature is -300 mV to + 300mV, meaning that when this gyro is just sitting on a table (not moving) it’s output will indicate erroneous rates anywhere between -150deg/sec to + 150 deg/sec rates!
But this is typical of other mems gyros, in other words mems gyros are generally worthless unless you temperature compensate them. You could put a temperature sensor near the gyro, but the senor may heat up at a different rate then the gyro, having the sensor right on the die is what you want, it’s strange they don’t have one, unless I am missing something obvious.
Given that these were originally targeted at camera stabilization, I’d guess they might high pass the sucker and just look at the rate of change instead. If you’re tracking a target with your camera, you don’t care how fast you turn, you care how jerky it is. Explains a bit that way, doesn’t it.
SOI_Sentinel:
Given that these were originally targeted at camera stabilization, I’d guess they might high pass the sucker and just look at the rate of change instead. If you’re tracking a target with your camera, you don’t care how fast you turn, you care how jerky it is. Explains a bit that way, doesn’t it.
Ok, that probably explains it, I emailed the applicaton engineer about this and he was kinda surpised I needed to do this, I guess most applications look only at rate of change as you said.
JC: Question:If I use three single axis gyros, could I use the temp reading from only one gyro, or should I use each gyro’s own temp reading???
As mentioned above, it sounds as though the temp of interest is the device’s internal temp.
Jeff
Yes you want the temperature of the die, ideally, you should use all three, the temperature of a pc board varies quite a bit along the board, if you have one sensor on the main board and another mounted 90 degrees from it, they will heat up/cool down at different rates. But it depends on the application, if you have an IMU in a rocket, for instance, and it power ups, runs for a few minutes and powers down, everything is going to be at the same temperature, so it really doesn’t matter.