Adding Wireless Serial Communication


For this expansion, I recommend the following products from Pololu.

Although the m3pi expansion kit comes with other components, we will only be using the following.

  • 1 m3pi expansion PCB
  • 1 2x7 extended male header
  • 2 1x2 extended male headers
  • 3 1x2 male headers
  • 3 shorting blocks
  • 1 push button
  • 1 1x11 female header
  • 1 1x12 female header
  • 1 1x2 female header
  • 2 1x2 female headers (for the 3pi)
  • 1 2x7 female header (for the 3pi)

Please note the following before beginning.

  • If you have purchased the 3pi (not the m3pi) expansion board, you will need to solder in voltage dividers to avoid frying your Wixel. The m3pi expansion PCB comes with these components already soldered in. You can find more information in the Wixel User's Guide on this topic, and the m3pi User's Guide on this topic.
  • You should only solder on the Wixel headers (1x11 and 1x12 female headers) if you are certain you do not want to install an XBee controller, since the installation of the Wixel headers prevents the use of an XBee, due to the height of the headers. You can find more information on this here.
  • Also note that you don't need to do what I did, which is solder the unneeded USB connector onto the wrong side of the m3pi board, and then spend the next hour desoldering it (which was a pain in the ass). In short, be careful to solder the components onto the correct side of the expansion board!

The next sections describe the complete process of installing the m3pi expansion PCB for the purposes of wireless serial communication using a Wixel. However, feel free to view Pololu's m3pi expansion kit's assembly instructions and connection instructions.

Installation of components onto m3pi PCB

The image below of the PCB's underside shows where to solder the components onto the PCB. When soldering the extended male headers, ensure that you solder the shortest ends, and that the longer ends of all extended male headers point downwards, so they can connect into the female headers we will solder onto the 3pi. Be very careful to ensure that the extended male headers are soldered in straight, otherwise you'll have a tough time getting them into the female headers of the 3pi. All other components are soldered facing upwards. Since it can be tough to work around the extended male headers, solder these in last. Also, remember to attach the 3 shorting blocks to the 3 1x2 male headers when you are done.

Installation of components onto the 3pi

The image below of the 3pi's underside shows where to solder the components onto the 3pi. This can be tricky because of all the other components already present. Even if you have (unbelievably!) unsteady hands like myself, you should be fine if you are careful.

Assembly and wireless setup

Use the 4 screws, spacers and bolts to attach the expansion PCB to the 3pi. Doing so will make it difficult to replace the batteries, so you can use the 1x2 female header on the expansion PCB to charge the batteries (if you are using rechargeable ones). Make sure that your extended male headers all fit correctly into their corresponding female headers before you do this.

The last step is to flash the appropriate serial-forwarding app onto each Wixel. Instructions on how to do this are available in the Pololu Wixel user's guide.