SparkFun Forums

[Mobiuss]

Hi, the Sparkfun hookup instructions for the MCP4725 DAC show how to unsolder or cut the solder pads to get different addresses if you have more than 1 DAC stacked up, fine, but no clue as to what the addresses should be. So far whatever address I give each DAC, they all get the same signal. Also you can't have 3 arrays of 512 points, no enough memory.

[Mobiuss]

Thanks liaifat85, yes, but your link is for the chip alone, not on a Sparkfun board, so doesn't talk about the solder pads. Yes it has the device address and address bits in the first byte Figure 6.2, so how is this affected by the solder pads? Or, how do you change the address bits A0 A1 and A2?
So far I have a sine wave with 36 points, but the negative values don't go negative on my scope, they just go from max positive to zero and back up. So a negative looking half of sine wave is all above the time axis, not below.

[YellowDog]

Try putting a capacitor in line with the output and connect the scope past the cap.

[Mobiuss]

That makes the whole waveform centred about zero, but waveform has the same shape! Doesn't move the negative side of sine wave into negative voltage.

[YellowDog]

The MCP4725 has a single positive power supply so it can not generate negative voltage. (Just 0 to VCC)
You'll need to feed it's output into a opamp with positive and negative power rails to generate a negative voltage on the bottom half of the sine wave.

[Mobiuss]

Yes thanks YellowDog, that makes sense now. Actually I think I have sorted out this problem; I don't actually have to generate the negative side of sine wave after all, the 6x MOSFET switches will take care of it, after I've done a bit of soldering.
However the opamp option could be useful elsewhere, thanks.

[YellowDog]

Glad I could help!