user13242: I'm looking to connect an old GPSlim236 device to my Arduino via serial comms. I have seen references online on how to connect the device but in the data sheet it says TTL level between 3V - 5V.  Does this mean that the GPS can automatically switch between logic level 5V -3V when needed? 
Here is the link to data sheet for the GPS - http://www.holux.com/JCore/UploadFile/3205400.pdf

user10794: The datasheet says:

Power Supply 
External Voltage: 5VDC +/- 10% 

So I take that to mean you supply 5V to it.

Later on it says:

Transmit Data. From organizer to peripheral. (Voltage Level is 3.3V ~ 5.0V)

I presume that means that it will supply (or accept) 3.3V to 5V as a high level, and less than 3.3V as a low level. This is perfectly normal for an Arduino.


Does this mean that the GPS can automatically switch between logic level 5v -3v when needed ? 

No I would not read it like that. If you read the datasheet for the Arduino processor chips it states things like an output high is a range of voltages, similar to what this device is saying. A "high" is not necessarily 5V exactly, it might be 4.7V, for example. However the Arduino input pins are similarly designed to take a range of voltages.


My confusion here is that the datasheet says 3-5v but what if I connect the device to a raspberry pi which (I think) only accepts 3v, would it still work?

Well, the datasheet says 5V +/- 10% for charging the internal battery. I'm not sure what your situation is if you are trying to run it from a Pi.

13242: <p>I'm looking to connect an old GPSlim236 device to my Arduino via serial comms. I have seen references online on how to connect the device but in the data sheet it says TTL level between 3V - 5V.  Does this mean that the GPS can automatically switch between logic level 5V -3V when needed? </p>

<p>Here is the link to data sheet for the GPS - <a href="http://www.holux.com/JCore/UploadFile/3205400.pdf" rel="nofollow">http://www.holux.com/JCore/UploadFile/3205400.pdf</a></p>
 10794: <p>The datasheet says:</p>

<blockquote>
  <p>Power Supply </p>
  
  <p>External Voltage: 5VDC +/- 10% </p>
</blockquote>

<p>So I take that to mean you supply 5V to it.</p>

<hr>

<p>Later on it says:</p>

<blockquote>
  <p>Transmit Data. From organizer to peripheral. (Voltage Level is 3.3V ~ 5.0V)</p>
</blockquote>

<p>I presume that means that it will supply (or accept) 3.3V to 5V as a high level, and less than 3.3V as a low level. This is perfectly normal for an Arduino.</p>

<hr>

<blockquote>
  <p>Does this mean that the GPS can automatically switch between logic level 5v -3v when needed ? </p>
</blockquote>

<p>No I would not read it like that. If you read the datasheet for the Arduino processor chips it states things like an output high is a range of voltages, similar to what this device is saying. A "high" is not necessarily 5V exactly, it might be 4.7V, for example. However the Arduino input pins are similarly designed to take a range of voltages.</p>

<hr>

<blockquote>
  <p>My confusion here is that the datasheet says 3-5v but what if I connect the device to a raspberry pi which (I think) only accepts 3v, would it still work?</p>
</blockquote>

<p>Well, the datasheet says 5V +/- 10% for charging the internal battery. I'm not sure what your situation is if you are trying to run it from a Pi.</p>
