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Old 06-17-2013, 05:28 AM #1
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Default Converting XY points to DAC values

I have an XY galvo and want to make a control card.

If I have values (0,0) (0,10) (10,10), (0,0) eg a square, how do I convert these XY values to voltages?

My understanding is that the angle the mirror rotate is supposed to be linear between -5v and +5v eg if I get it 0 volts then the mirror should rotate to 0 degrees, if I give it +5v it should go to say +20degrees so +2.5v=10degrees.

Playing with my galvo I see if I adjust the X galvo from -5v to +5v it will scan a straight line but if I scan the Y galvo the line is not vertical if the X galvo is not at 0v.

Anyone have the equations for the function (volts_A,volts_B)=function(x,y) ?


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Old 06-17-2013, 07:14 PM #2
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Default Re: Converting XY points to DAC values

It depends on what kind of DAC you are using.

I find that the Arduino DUE board is most easy one.

Code:
analogWrite(DAC1, valx );
analogWrite(DAC0, valy);
That's it!
And its biggest advantage is that both DACs are updated at the same time.


Or with MCP4725:

Code:
 Wire.beginTransmission(DACX);  
 Wire.send(64);                // cmd to update the DAC  
 Wire.send(valx >> 4);         // the 8 most significant bits...
 Wire.send((valx & 15) << 4);  // the 4 least significant bits...
 Wire.endTransmission();

 Wire.beginTransmission(DACY);  
 Wire.send(64);                // cmd to update the DAC  
 Wire.send(valy >> 4);         // the 8 most significant bits...
 Wire.send((valy & 15) << 4);  // the 4 least significant bits...
 Wire.endTransmission();
You need 2 separate DACs. You can not update them at the same time.
So no diagonally lines, only stair cases.


MCP4922 which is a dual DAC has latching capability but is is way to slow.

Have a look at this thread at LPF
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Last edited by camvo; 06-17-2013 at 07:17 PM.
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Old 06-17-2013, 07:20 PM #3
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Default Re: Converting XY points to DAC values

Im working with an SPI DAC, its ALOT faster than I2C once like MCP4725. Its easy to interface it if your reading the datasheet =)
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Old 06-17-2013, 08:59 PM #4
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Default Re: Converting XY points to DAC values

Quote:
Originally Posted by Sultanen View Post
Im working with an SPI DAC, its ALOT faster than I2C once like MCP4725. Its easy to interface it if your reading the datasheet =)
I set up a SPI DAC running at 8mhz clock and it tops out at about 700 points.
Any more points and the graphics starts to flicker.

The DAC / processor Camvo is using loads the DAC by writing to the DAC registers directly, so only takes a few clock cycles, therfore the limiting factor is the scanners not the SPI bandwidth.

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