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[Reply #15 on:]

By using mains power adapters.

[Reply #16 on:]

Is that a negative voltage, or just ground (0V)?

[Reply #17 on:]

No it is a negative voltage.

Voltages are a relative measure, they are always measured with reference to some other potential. If you connect the positive end of a supply to ground the other end is a negative voltage (with respect to ground)

[Reply #18 on:]

Really!?!?!?! So arduino 5V+Wall wart 6V can make +5V to -6V?

[Reply #19 on:]

No that's not what I said.

[Reply #20 on:]

Okay, then some help. I have arduino's +5V and a 6V wall wart.

[Reply #21 on:]

Okay, so find a mating connector for the 6V wallwart and wire the +6 to the arduino ground and the wallwart 6V return  becomes -6V. (or cut the end off and solder on pins so you can stick them in a breadboard).
Then find an op amp that is happy running from +/- supplies, like a TL072, TL074.
Take the Arduino DAC output, run it thru a cap in to the op amp set up as a voltage follower or very low gain inverting amplifier.
http://focus.ti.com/lit/ds/symlink/tl071b.pdf
I am using 0.47uF caps (ran out of 1uF caps) into a MOSFET to make an audio amp to play a Tone melody quite loudly in a fencing club to signal when a touch is made.

What are you trying to do?

[Reply #22 on:]

I'm trying to make a sine wave. would the LM358 work? it has two op amps so I can make a sine wave. the DAC is for making tones.

[Reply #23 on:]

Data sheet says its good for +/- supplies.

[Reply #24 on:]

Perhaps you don't even need a negative voltage.

IF I understood correctly, you're trying to generate a bipolar signal (sine wave) using the Arduino, and a Unipolar DAC.  You cannot produce DC negative voltages with this hardware.  But you CAN produce AC audio signals regardless, and WITHOUT using bipolar supplies.  

You have the Arduino which cannot output anything negative.  You have your DAC (which by description is Unipolar).  Research Bipolar DACs to understand the difference.

Either way, you cannot produce negative voltages directly BUT...  suppose you want to produce a Sine Wave, and you decide that your resolution is +/- 127, meaning 7 bits with sign.  Write your CODE such that in calculating Amplitude of the SINE, comes up with a 7 bit result (0-127, negative or positive) which is then simply ADDED to 128...  Feed that to the DAC.

Follow me here.  Your result +/- 127 is added to 128, producing a result which is between 1 and 255.  This is in the range of the 8 bit DAC, representing a +/- excursion which is atypical of a bipolar output, but is otherwise a positive voltage.  

Now AC couple this DAC output voltage to your audio amplifier.  Capacitive coupling if you will.  This is the answer without resorting to bipolar solutions; if you don't know what this means, do some research in AC coupling.

HTH, DHM

[Reply #25 on:]

So I'm basically generating a sine wave with an offset of about 2.5 volts.
And now some more help.
How can I send the data over the Wire library? I don't exactly understand how to do it.

[Reply #26 on:]

ICL7660

http://www.intersil.com/data/fn/fn3072.pdf

This chip can generate -5V from a +5V source.

[Reply #27 on:]

Yay! and pins:
1 No connection
2 Capacitor? What value?
3 0V
4 Cap negative pole from pin 2
5 negative voltage
6 What's This?
7 And this?
8 5V in

[Reply #28 on:]

How about this one:
http://www.sparkfun.com/products/316
It has two converters inside, but seems quite similar otherwise.

[Reply #29 on:]

I think you need to slow down and try to understand the magic of what a simple series capacitor can do for you to pass audio information from one device to another. Maybe if you could just draw a crude block diagram of what all is involved in your project, as in:

Arduino>>>D/A module>>>audio device??? With a short description of what you think each device needs to accomplish for your end goal?

It's that last device that needs to be explained better to us, to stand a better chance to get useful recommendations or suggestions on how to accomplish your goals.

Lefty