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VEX Cortex I2C NXT Cable HOWTO

As promised,here’s an easy to follow HOWTO for making your own VEX Cortex to NXT converter cable for I2C sensors. Please keep in mind a few things:

  • Do this at your own risk
  • This won’t work with sensors that require 9V to operate
  • This won’t work with analogue sensors
  • Do this at your own risk

You will need the following:

  • A soldering iron
  • Soldering tin
  • Something to hold the cables while you solder.  I like to use one of those Helping Hands soldering aids.
  • Electrical tape
  • Small knife to strip wires
  • Wire cutter
  • 2 VEX sensor cables.  I used ones snipped from broken sensors
  • NXT sensor cable cut in half
Step 1

Split the individual wires of one of the VEX sensor cables and cut the red and black ones back, you won’t need them. Strip about 2-3mm off the top of the white wire.

Write SDA on this cable’s connector or label it in some other manner.

Step 2

CIMG0314Split the individual wires of the other VEX sensor cable. Strip about 2-3mm off the top of each wire.

Write SCL on this cable’s connector or label it in some other manner.

Step 3

Strip 1 cm of the NXT cable’s black cover, split the individual wires and strip about 2-3mm off the top of each wire’s cover. Snip off the white wire, you won’t need it. When stripping the black cover from the NXT cable, take care not to nick the wires in it, it’s very easy to do and can result in short circuits later.

Step 4

Tin all of the exposed wire tips, this will make soldering them together later much easier.

Step 5

Solder all the wires together as follows:

  • NXT green to VEX red (+4.3V)
  • NXT black and red to VEX black (GND)
  • NXT yellow to VEX white with SCL label
  • NXT blue to VEX white with SDA label
Step 6

Wrap each soldered joint in the electrical tape. This is a real pain but will stop short circuits, so make sure you take care doing this properly.

Step 7

Wrap all of the individual wires in tape, make sure the ends are really stuck. I usually wrap some extra around the ends.

Step 8

You’re done!

I will publish the I2C master code very shortly so you can start playing with it yourself.

About Xander

Xander Soldaat is a Software Engineer and former Infrastructure Architect. He loves building and programming robots. He recently had the opportunity to turn his robotics hobby into his profession and has started working for Robomatter, the makers of ROBOTC and Robot Virtual Words.