user23487: This is my very first Arduino project. I want to learn about GPS navigation by exploring the NMEA protocol!
Therefore, I bought a WeeBee GPS module. After reading the datasheet, I have two questions:

The official Arduino website states 

Note: if you are using an Arduino Uno, keep in mind that you can't use the GPS module at the same time as your computer is connected on the USB port.

But I you go to the end of his tutorial, you will see he can transmit the GPS data to his computer. I don't understand why it would not be possible...
The GPS module datasheet (download link here) states that the maximum voltage is 5V. But it also states 


serial connections are 3.3V CMOS Logic Levels

and 

Suitable decoupling must be provided by external decoupling circuitry.

So, does it mean I need a logic level converter to prevent damage to the GPS module?

user11763: 
The article on the Arduino website means that you can't upload sketches from your PC to the Arduino or receive any sort of data, through the serial monitor or otherwise, from your PC, while the GPS module uses the RX pin. Any attempt to send data from PC to Uno in this condition would cause the Arduino to receive only corrupted data, since 2 devices (GPS module and PC) would be trying to send data at the same time, with the same line. This limitation is easily resolved by connecting the GPS module to a SoftwareSerial port instead; this keeps the HardwareSerial port (pins 0 & 1) free for bidirectional PC-Arduino communication.
The datasheet says that the maximum power supply voltage is 5 V. However, the serial connections are 3.3 V logic, so yes, you will need logic level shifters. A simple voltage divider will serve. However, 'external decoupling' refers to circuitry used in decoupling/smoothing out any spikes or dips that may occur in the supply voltage. An untamed spike could damage the device, while a dip (perhaps from large current draw) could cause the device to stop working, if the voltage falls low enough to be considered under-voltage. A 10uF electrolytic capacitor, connected from Vcc to GND close to the GPS module, should be okay.


23487: <p>This is my very first Arduino project. I want to learn about GPS navigation by exploring the <a href="https://en.wikipedia.org/wiki/NMEA_0183" rel="nofollow noreferrer">NMEA protocol</a>!</p>

<p>Therefore, I bought a WeeBee GPS module. After reading the datasheet, I have two questions:</p>

<ol>
<li><p>The <a href="http://playground.arduino.cc/Tutorials/GPS" rel="nofollow noreferrer">official Arduino website</a> states </p>

<blockquote>
  <p>Note: if you are using an Arduino Uno, keep in mind that you can't use the GPS module at the same time as your computer is connected on the USB port.</p>
</blockquote>

<p>But I you go to the end of his tutorial, you will see he can transmit the GPS data to his computer. I don't understand why it would not be possible...</p></li>
<li><p>The GPS module datasheet (<a href="http://pan.baidu.com/s/1hsrWhoC#path=%252FWeBee%252FGP-001" rel="nofollow noreferrer">download link here</a>) states that the maximum voltage is 5V. But it also states </p></li>
</ol>

<blockquote>
  <p>serial connections are 3.3V CMOS Logic Levels</p>
</blockquote>

<p>and </p>

<blockquote>
  <p>Suitable decoupling must be provided by external decoupling circuitry.</p>
</blockquote>

<p>So, does it mean I need a logic level converter to prevent damage to the GPS module?</p>
 11763: <ul>
<li>The article on the Arduino website means that you can't upload sketches from your PC to the Arduino or receive any sort of data, through the serial monitor or otherwise, from your PC, while the GPS module uses the RX pin. Any attempt to send data from PC to Uno in this condition would cause the Arduino to receive only corrupted data, since 2 devices (GPS module and PC) would be trying to send data <em>at the same time</em>, <em>with the same line</em>. This limitation is easily resolved by connecting the GPS module to a <code>SoftwareSerial</code> port instead; this keeps the <code>HardwareSerial</code> port (pins 0 &amp; 1) free for bidirectional PC-Arduino communication.</li>
<li>The datasheet says that the maximum power supply voltage is 5 V. However, the serial connections are 3.3 V logic, so yes, you will need logic level shifters. A simple voltage divider will serve. However, 'external decoupling' refers to circuitry used in decoupling/smoothing out any spikes or dips that may occur in the supply voltage. An untamed spike could damage the device, while a dip (perhaps from large current draw) could cause the device to stop working, if the voltage falls low enough to be considered under-voltage. A 10uF electrolytic capacitor, connected from Vcc to GND close to the GPS module, should be okay.</li>
</ul>
