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Firstly, I'm a hobbyist and have a lot to learn.

I'm trying to get a 0-5V signal created by a microcontroller to +/-2V audio level.

I don't want to spend a lot and would like to keep the part count down, so I started experimenting using resistor dividers and I can get it into either the 0-2V or 0-4V range.

But I don't know how to make the signal go negative. What are some ways to do that?

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    \$\begingroup\$ You can't get negative voltage out of positive supply using resistors (unless considering different reference). \$\endgroup\$ – Eugene Sh. Jul 6 '15 at 16:50
  • \$\begingroup\$ I wondered if that was the case. I'm looking for other solutions. \$\endgroup\$ – Sam Washburn Jul 6 '15 at 16:51
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    \$\begingroup\$ No, you need the impedance of the next stage. Typical impedance for headphones is 32ohm. \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 6 '15 at 17:04
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    \$\begingroup\$ To cancel the effect of the load you can put an amplifier stage with designed input impedance. But it will get your circuit a way more complicated. \$\endgroup\$ – Eugene Sh. Jul 6 '15 at 17:06
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    \$\begingroup\$ Electrolytic capacitors are commonly used for this. Try to find a bipolar if you can though. \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 6 '15 at 17:23
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I'm going to make an assumption here because you didn't provide enough information.

Specifically, I assume that this is an analog signal that ranges from 0V through +5V.

The solution is simple. All you need to do is to capacitively-couple the signal from the controller output network into your destination device.

I'm going to make a couple more assumptions here:

1) The output impedance from the controller and its output network is fairly low.

2) The input impedance of the device that you are trying to feed is fairly high.

schematic

simulate this circuit – Schematic created using CircuitLab

I'm showing a polarized capacitor because that is the most common. The (+) side of the capacitor goes to the node with the most positive (highest) average DC voltage. That would be from your microcontroller: the average voltage is about 2.5 Vdc assuming that the signal swings all the way from 0V to 5V.

It's really that simple!

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  • \$\begingroup\$ What is the 10KΩ resistor for? \$\endgroup\$ – Sam Washburn Jul 7 '15 at 0:34
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    \$\begingroup\$ @SamWashburn: If your destination is say an opamp, you will need a resistor to have DC path for its input bias current. Otherwise funny problems can occur. Also the cap needs to discharge somehow when you pull the power or else it can give nasty pops when plug stuff in again if it's charged. A resistor is the simplest way to ensure that. \$\endgroup\$ – Fizz Sep 25 '15 at 8:05

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