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What does the 74LVC1G125 do on the Arduino wireless sheild? Its just a buffer, but is it really necessary, or is it only necessary if you stack a lot of shields? (ie: collectively increasing input impedance)

Its this shield: http://arduino.cc/en/Main/ArduinoWirelessProtoShield

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    \$\begingroup\$ link to shield plz? \$\endgroup\$
    – NickHalden
    Oct 10, 2012 at 22:14
  • \$\begingroup\$ You need to provide a link to the specific shield you're talking about; you can't expect us to guess if you want anything other than a generic answer. \$\endgroup\$
    – Dave Tweed
    Oct 11, 2012 at 4:21
  • \$\begingroup\$ arduino.cc/en/Main/ArduinoWirelessProtoShield \$\endgroup\$
    – SpiRail
    Oct 11, 2012 at 8:31

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The input of the 74LVC1G125 is 5V-tolerant, while the DIN pin of the Xbee module may or may not be. The gate is there to provide level translation, as this is the only signal that flows from the Arduino to the Xbee module.

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It could be used for a number of reasons. One use can be a more powerful driver if you need more current. Another reason can be to protect a more expensive part from ESD damage or shorts which tends to happen to an exposed I/O. It's cheaper to replace a buffer than a processor! Another reason could be to keep return paths short, reducing loop area inductance (helps with signal integrity and EMI).

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  • \$\begingroup\$ That's a lot of speculation. The question as it stands can't be answered. \$\endgroup\$
    – stevenvh
    Oct 11, 2012 at 7:45
  • \$\begingroup\$ I put a reference to the shield (anyone who looks on the Arduino home page would find it there, so i never thought a link would be requred) the question can be answered... as it stands. Because someone put the buffer there for a reason. \$\endgroup\$
    – SpiRail
    Oct 11, 2012 at 8:34
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    \$\begingroup\$ @SpiRail - A lot of people, myself included, will use Google when searching for information. A search for "Arduino wireless shield" showed several different types of shield. There's no law that says I have to go to the Arduino site. Never assume others are looking at the same website as you are; adding a link has never hurt anyone (not as far as I know). \$\endgroup\$
    – stevenvh
    Oct 11, 2012 at 8:48
  • \$\begingroup\$ : D I made an assumption... It was a "bad assumption". None the less, the link is there now. I also asked on the Arduino forums and someone is suggesting that its because the xbee chips are a different voltage in some cases. But all the speculation from Analog Arsonist makes sense as well. \$\endgroup\$
    – SpiRail
    Oct 11, 2012 at 11:45
  • \$\begingroup\$ It's speculation but there are only a finite number of reasons to use a buffer and I named most of them. It could be level translation from 5V to 3.3V..the Arduino is 5V I/O right? \$\endgroup\$ Oct 11, 2012 at 14:02

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