Getting started with the DigiX - Part 1 of 2

This is the first part of my project to integrate the Digistump DigiX board with the BeagleBone. In this post, I'll provide a review of the DigiX and some of the good and less good points about working with it. The next section will describe in more detail the software and process I used to build the project.

First, for your multimedia viewing pleasure,  here is a quick video tour of this fairly simple project:

Introducing the DigiX

The DigiX is produced by DigiStump which was founded in 2012 by Mr. Erik Kettenburg in the Seattle area. I first became aware of them when I backed his successful Kickstarter for the DigiSpark which is a super-small $9 Arduino development board  - I will include them in a later part of my monitoring system. A few months after the DigiSpark shipped, I saw the Kickstarter come up for the DigiX and decided to go for it.

The specs on the DigiX are, frankly over the top! This is the Monster Killer Arduino of all Time (at least for now) - check it out:

In form factor, it looks a bit similar to the Arduino Due, but it has a double row of IO pins down the one side whereas the Due only has a single row.

This is a beast!! As well it has BOTH on-board wifi and mesh networking via the popular, low-cost nRF24L01+ wireless module and and a micro SD card slot. All this for only $69.95 USD!

 That being said, given that the BeagleBone Black is only $44.95 and the RaspBerry Pi is only $39.95 (prices from SparkFun) and both of them run full up Linux. Is it worth the extra money to have the DigiX? Here are a few thoughts on pros and cons...

Pros

1. Rather than having to wrestle with the complexity of managing GPIO in the Linux environment, the DigiX supports the usual Arduino IDE and it's familiar interface. If you're used to stock Arduinos, then there is no ramp up.
2. The onboard wifi works as advertised and is a breeze to configure according to the DigiX Wiki article (check it out here).
3. There are more IO pins than any reasonable person could ever use and there is loads of program memory space (524,288 bytes).
4. There is a good range of sample programs that exercise the functionality of the board and they all seem to compile and work right away. I was amazed that I had a simple web server up and running in about 15 minutes!
5. I haven't tried the mesh networking yet, but I am assuming it works and it's awesome to have it on the same board.
6. This board is a 3.3 VDC board (like the other newer Arduinos), but Digistump sells a level shifting shield so you can reuse older 5 VDC shields, which is very useful if you're an old-timer like me.
7. There is a reasonable amount of documentation and active forums for help.

Cons


The main draw back is is it not quite a stock Arduino and a couple of compromises have been made to keep the board affordable. Let's look at two things I have found...

Wifi

The wifi module on the DigiX is not the same as on the Arduino Yun. The Yun uses the AR9331 while the DigiX uses an Atheros Silicon based embedded UART/WiFi module(source here). This means the DigiFi wifi library is mostly compatible with the Arduino Ethernet library, but not 100%.

Consequently, for the project I just completed, I wanted to use Socket.io or websockets to exchange information between my Beaglebone and the DigiX. I tried various sockets libraries and just could not find a way to make them work with the DigiX! I posted a thread to the DigiX forums, but, since they're somewhat less active than the Arduino boards, I so far haven't found a solution. You will see in my upcoming project that the solution I found works, but is definitely "suboptimal" from a design standpoint.

USB Serial and programming

Mr. Kettenburg provides a good technical description of what happens with USB serial on the DigiX and Due boards here. You can read the detailed explanation, but what it boils down to is that the Arduino Due has two USB ports - one for programming and one for native USB - while the DigiX has only one USB port which has to work for programming and USB. Unfortunately, on the DigiX it seems to sometimes be a coin toss as to which is going to be available when you boot up the board, which caused me some headaches at first.

When I was first using the board, it would do something like this when doing programming:

1. The Arduino IDE is set on COM16 and you hit the upload button in the IDE.
2. The program compiles and if there are no errors, then it goes to upload and says "The COM port isn't available".
3. Restart the DigiX and if you are lucky it comes up with COM15.
4. While on COM15, hit the upload button and it goes through and programs the board.
5. However when you go to the IDE to select the serial port for the serial monitor, it is back to COM16!

This could be a huge hassle sometimes requiring multiple restarts of the board and plugging and unplugging the USB until the right port came up. As well, the IDE serial monitor would sometimes not fire up and that required more restarts.

At the moment, I seem to have solved this and it is working smoothly. What I did was follow this advice from the DigiX wiki:

If the COM port isn't showing in the Arduino IDE - unplug and replug the board. If that doesn't work - while plugged in, hold down the erase button on the board for a moment and then unplug and replug - you may then have to select it from the com port menu as it may be on a different port - but it is a sure way to get it to respond even if your sketch crashed the USB stack. 

At the same time as doing this, I moved it to another USB port on my system and Windows reloaded the drivers. It works normally now, but it leaves me concerned it will stop working again in the future. I guess I shouldn't complain because it is a bit of an RTFM situation, but perhaps future versions of the board could have the two port solution like the Due or maybe a jumper block to put the USB port into one mode or the other to avoid this confusion?

Summary

Despite the minor hassles I would still say the DigiX is a great board and worth the money. It gives you loads of room to grow and build very sophisticated networked projects. If you just want something relatively simple to take some digital/analog inputs and then do some digital.analog outputs, then this board may be too much and you should look at some of the simpler Arduinos on the market.

As the "Internet of Things" movement develops, it will be de rigueur to be able to to hook your embedded project to the Internet and to other devices via either mesh or Bluetooth Low Energy. The DigiX has you covered with wifi and mesh on board and while it is more expensive than some boards, you save by having all the connectivity integrated and not having to get separate shields and so on.

Nest up, the software the drives this project!