test high speed I2C mode

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Re: test high speed I2C mode

Postby gloomyandy » Sat Jun 25, 2011 10:40 pm

Hi Aswin,
I've just placed an order for blinkm. So once that arrives i should be able to try and get that working. It will be interesting to see what the problem is... The blinkm looks like an interesting device...

Andy
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Re: test high speed I2C mode

Postby Aswin » Sat Jun 25, 2011 11:40 pm

The BlinkM is great for debugging mobile robots. The colored led can give you all kinds of information in situations where you can't read the screen. I'll supply a java class for it.
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Re: test high speed I2C mode

Postby Aswin » Sun Jun 26, 2011 10:37 am

Hi Andy and others,

I got my sensor working in HIGH_SPEED mode (125K).

You might remember I had three sensors on one sensor port, a gyro and accelerometer that are both part of an IMU sensor and a BlinkM all color LED.
This was a design error in the first place. Because within the limits of a single port you can query only one sensor at a time. The IMU needs to be as fast as possible to get valuable information. This means that every message to the BlinkM slows down the IMU. For this reason I decided to remove the BlinkM from my sensor and guess what, the IMU runs at high speed I2C without any problem.

It now takes about 2.6 ms to query both sensors ( 2 * 6 bytes) and to process the raw signal for calibration and unit conversion. I am really glad with this, this is about 4 times faster as I could get with robotC. My investment learning java and Lejos has paid of. Next step will be to recreate my nonlinear complementary filter to fuse rate and acceleration info.

I'll make a different sensor altogether from the BlinkM. I want a housing that can be daisy chained so that I can have more than one on the same sensor port (Oh no, I'm making the same mistake again!).

Thanks for all the help.
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Re: test high speed I2C mode

Postby bullestock » Sun Jun 26, 2011 1:04 pm

Aswin wrote:[...] within the limits of a single port you can query only one sensor at a time. The IMU needs to be as fast as possible to get valuable information. This means that every message to the BlinkM slows down the IMU. For this reason I decided to remove the BlinkM from my sensor and guess what, the IMU runs at high speed I2C without any problem.

Could you not just ignore the blinkM device (i.e. not query it)?
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Re: test high speed I2C mode

Postby gloomyandy » Sun Jun 26, 2011 1:43 pm

Hi bullestock,
My understanding is that just having the blinkm atached to the same port was stopping one of the other sensors from working. So even if it was not being used it still caused problems. So it makes sense to move it to another port...

Aswin, great news that you have the main sensors working. Looking forward to seeing what you are going to do with it....

Andy
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