Although most Arduino and compatible boards can generate varying signals using pulse-width modulation, they lack the ability to generate true output signals that vary in voltage - in other words a digital-to-analogue converter. One method to do this is with a dedicated DAC chip, however if you're short on time or funds, you can create such signals with a simple resistor and capacitor acting as a low-pass filter. This method has been documented and demonstrated by the folks at Jeelabs, and is quite successful:
Not only is that a useful function, there's also some interesting analogue theory as well. So head over to the tutorial for more information. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
When adding external circuitry such as the low-pass filter described above to your next Arduino project, and need to make it more permanent than using a solderless breadboard - consider our range of ProtoShields. From the tiny LeoStick to the Mega range, we offer a complete range for you to work with.