user693: I'm completely new with Arduino and microcontrollers in general.
I have several 5V sensors, and need 3.3V because that's the max for the Due. Is it possible to use a resistor to connect it to the Arduino? Do I have to measure the current from the sensor and calculate the needed resistor like this?
$$\frac{5.0 - 3.3}{\text{Measured current}}$$
(5.0 - 3.3)/(Measured current)


user84: Well if you're not sure of what you're doing, you can always go with level-converters for your sensors (that does not apply to shields though)
Level-converters (sometimes called level-shifters) come in different flavors:

breakout board (the easiest to work with)
IC
DIY circuits with a few components

Some are "one-way": they have pin-pairs with converters 3.3V -> 5V, and other pin-pairs with 5V -> 3.3V conversion; others are bi-directional, i.e. you can use the same pair of pins in 2 directions 3.3V <-> 5V.
There are plenty of these converters, and they are rather cheap; here are just a few examples:

one-way breakout usable with 4 pairs of pins
bi-directional breakout usable with 4 pairs of pins
74HC4050 IC discussed here


693: <p>I'm completely new with Arduino and microcontrollers in general.</p>

<p>I have several 5V sensors, and need 3.3V because that's the max for the Due. Is it possible to use a resistor to connect it to the Arduino? Do I have to measure the current from the sensor and calculate the needed resistor like this?</p>

<pre><code>$$\frac{5.0 - 3.3}{\text{Measured current}}$$
(5.0 - 3.3)/(Measured current)
</code></pre>
 84: <p>Well if you're not sure of what you're doing, you can always go with <strong>level-converters</strong> for your sensors (that does not apply to shields though)</p>

<p>Level-converters (sometimes called <strong>level-shifters</strong>) come in different flavors:</p>

<ul>
<li>breakout board (the easiest to work with)</li>
<li>IC</li>
<li>DIY circuits with a few components</li>
</ul>

<p>Some are "one-way": they have pin-pairs with converters 3.3V -> 5V, and other pin-pairs with 5V -> 3.3V conversion; others are bi-directional, i.e. you can use the same pair of pins in 2 directions 3.3V &lt;-> 5V.</p>

<p>There are plenty of these converters, and they are rather cheap; here are just a few examples:</p>

<ul>
<li><a href="https://www.sparkfun.com/products/11978" rel="nofollow">one-way breakout</a> usable with 4 pairs of pins</li>
<li><a href="https://www.sparkfun.com/products/12009" rel="nofollow">bi-directional breakout</a> usable with 4 pairs of pins</li>
<li>74HC4050 IC discussed <a href="http://forum.arduino.cc/index.php?topic=109493.0" rel="nofollow">here</a></li>
</ul>
