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mpthompson
Joined: 02 Jan 2006
Posts: 650
Location: San Carlos, CA
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 Posted: Wed May 16, 2007 4:18 pm Post subject: |
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I think this is something you'll have to experiment with. Since you don't have a human in the loop you may consider using a magnetic compass to correct for drift over time. I think a lot of this is your specific application and how tolerable it is to drift. For instance, do you want better than 1 degree accuracy of an sample, or are you looking just to maintain a general direction and your application can tolerate +/-15 degree accuracy for maintaining such a general heading.
Mike |
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HakBot
Joined: 31 Jul 2006
Posts: 14
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| Posted: Thu May 17, 2007 7:24 pm Post subject: |
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| within a few deg is fine |
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HakBot
Joined: 31 Jul 2006
Posts: 14
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| Posted: Mon May 21, 2007 9:21 pm Post subject: |
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Mike,
Question for you. I'm planning on using a pic18f4550 to get readings from my IDG-300 I just received. My question is, do I take the readings via the normal analog inputs. Im reading my accelerometer this way. Thanks! |
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mpthompson
Joined: 02 Jan 2006
Posts: 650
Location: San Carlos, CA
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| Posted: Mon May 21, 2007 9:38 pm Post subject: |
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Well, I'm using the regular ADC inputs on an AVR ATmega168 to read both the accelerometer and gyro data. I did run into some issues because I believe the outputs are higher impedence than desired by the AVR ADC circuitry (about 10K ohms). To get better readings I always take two readings in a row and throw out the first. I don't know if you'll have the same issues with the PIC, but it is at least something to be aware of.
-Mike |
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Cliff
Joined: 23 Jan 2007
Posts: 150
Location: Saratoga, CA
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| Posted: Tue May 22, 2007 11:53 am Post subject: |
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Hi Mike, HakBot
| Mike wrote: | | I did run into some issues because I believe the outputs are higher impedence than desired by the AVR ADC circuitry (about 10K ohms). |
You can effectively reduce the impedance of the 10K output by using a 100pF to 1000pF capacitor to ground, on the input to the ADC. When the ADC samples it is charging an internal sample capacitor, so having a high impedance source will result in an error caused by the RC time constant of the internal capacitor and the source resistance. By adding a capacitor to the ADC input (which will charge between ADC samples), the current needed to charge the internal sample capacitor is sourced by the added capacitor with a much lower effective resistance. Adding the input capacitor will, of course, filter the input signal, but even with 1000pF, the low pass filter time constant will be of the same order as the sample time - so I'm not sure this would be a problem.
The best solution would be to insert an Op-Amp, configured as a voltage follower. This would not be friendly to add to an existing processor board, but for a new design it should be considered.
Cliff |
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HakBot
Joined: 31 Jul 2006
Posts: 14
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| Posted: Wed May 23, 2007 2:21 pm Post subject: |
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Hey Mike,
How are you reducing (I can only assume your pic is running at 5V) the 5V down to the required 3.3V? I don't have a 3v regulator handy so I tried using a 242ohm and 470ohm resistors in a voltage divider but its dropping to 2v when the gyro is drawing current. Am I stuck with only using a voltage reg? |
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mpthompson
Joined: 02 Jan 2006
Posts: 650
Location: San Carlos, CA
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| Posted: Wed May 23, 2007 4:28 pm Post subject: |
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I'm using the TI LM317L adjustable voltage regulator. To drop the voltage to 3v I'm using R1=470ohms and R2=680ohms 1% resistors. Seems to work well.
-Mike |
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brandiex
Joined: 30 Dec 2009
Posts: 4
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| Posted: Sat Jan 02, 2010 11:35 am Post subject: |
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What kind of personality do you find endearing in a robot? If you can own a SPEAKING robot right now (so no R2-D2 types), what kind of a personality would you most like to have? A cynic like Hitchhiker's Marvin? A super-logical like Data? Something more human like David? Something cute? Something helpful? Something weird? Something else?
_____________________
market samurai ~ marketsamurai |
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