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This is Week 2! At the end of March we'll have as many as 10 great podcasts, amazing guests, Live Google Hangouts, blog posts, Twitter Chats on Wednesdays, and a huge collection of links and projects for you to explore.
Please note that I'm learning. I'm sure some of you are fantastic experts, while others are working on Hello World. If you find errors, naïve or otherwise, in my code or solution, DO let me know in the comments and I'll update this post with notes and asides so we can all learn!
I wanted to learn a little about Arduino this week. It's an huge and enthusiastic community based around an open-source electronics platform. The hardware is small and relatively inexpensive, and it brings hardware hacking to folks (like myself) that may not feel up to doing really low level electronics work. There or stackable "shields" you can plug on top and easily add new features, screens, sensors, and more.
There's lots of different choices for Arduino development, including some more interesting versions like the Intel Edison with Arduino Breakout Board. The Intel Edison supports not just Arduino, but also can run a full version of Yocto Linux, and can run Python and node.js. I have an older Arduino Atmega328 which was like $12.99, but I wanted a more flexible option that included on board Wi-Fi. Getting Wi-Fi connectivity is kind of a hassle if it's not built in.
The Arduino Yún is a great choice, but I figured I'd spend more for the Edison and get a lot more options. I also got the "Seeed Studio Grove Starter Kit." This is a cool Arduino Shield that lets me (and the kids) attached sensors, buttons, screens, and lots of other stuff without soldering!
I download the Arduino software, but also found that Intel now has a complete Integrated IoT Windows 64 Installer that will get everything you need to get started with the Intel Edison. It makes it REALLY easy to start.
I tried a few small "Sketches" out, turning on a light with a button press, and such.
But I wanted to make something more interesting to me personally. I'm a Type 1 Diabetic, and I wear an insulin pump and Dexcom Continuous Glucose Meter. They are connected to the cloud via a project called Nightscout. Nightscout takes my sugar values and pushes them into Azure, where they are available via a JSON web service.
NOTE: I've put my Arduino Sketch on GitHub here. https://github.com/shanselman/NightscoutArduinoPlayground
Nightscout has a /pebble endpoint that is used to feed the Pebble Watch Face and show folks their blood sugar on their wrist. I thought it would be cool to hook up an Arduino to get my blood sugar from the cloud and display it on an LCD. It'll show the current value, change the background to green/yellow/red to display risk, and then a custom character to show trends (flat, up, down, etc).
The JSON the Nightscout service returns looks like this, but I just want the "sgv" value and the "direction."
{
status: [{
now: 1426017007130
}],
bgs: [{
sgv: "102",
bgdelta: 2,
trend: 4,
direction: "Flat",
datetime: 1426016912000,
filtered: 115232,
unfiltered: 118368,
noise: 1,
rssi: 191,
battery: "59"
}]
} I needed to bring in three libraries to achieve my goal. Remember I want to:
- Connect to my Wi-Fi network
- Download some JSON and parse it
- Display values on an LCD screen
So I needed:
- #include <WiFi.h> //The Intel Edison has Wi-Fi built in
- #include <aJSON.h> //JSON is hard to parse on small memory devices, so this aJSON library helps
- #include "rgb_lcd.h" //I'm using the Grove - LCD RGB Backlight
As with all problems when you're learning new things, you'll want to break them down one at a time.
I wanted to just display a string on the LCD, that was easy, there's lots of examples online in the Arduino community.
lcd.clear();
lcd.setCursor(0, 0);
lcd.print("Hello World");
Connecting to Wi-Fi was pretty easy also:
while (status != WL_CONNECTED) {
// Connect to WPA/WPA2 network. Change this line if using open or WEP network:
status = WiFi.begin(ssid, pass);
// wait 3 seconds for connection:
lcd.setCursor(0, 0);
lcd.print("Waiting...");
delay(3000);
} When doing an HTTP call (given the libraries I was learning about) it's pretty low level. Constrained memory Arduinos (not like the Edison) don't seem to have SSL support, nor do they have high-level HTTP libraries. I had to craft the HTTP headers manually:
lcd.print("Connecting...");
if (client.connect(server, 80)) {
lcd.clear();
lcd.print("Server connected");
// Make a HTTP request:
client.println("GET /pebble HTTP/1.1");
client.println("Host: hanselsugars");
client.println("Connection: close");
client.println();
} Then I spin through the HTTP Response looking for the start of the JSON, and store it away. At this point I'm wondering if I'm doing it wrong. It isn't very robust.
boolean jsonFound = false;
int bytes = 0;
while (client.available()) {
char c = client.read();
//look for first {, yes it could be in a cookie but I'm thinking positively.
if (c == '{') jsonFound = true;
if (!jsonFound) continue;
stringBuffer[bytes++] = c;
if (bytes >= MAXBUFFER) break; //that's all we have room for or we're done
}
Then once I've got the stringBuffer, I use the aJSON library to get the values I need. This isn't pretty, but it's how you use this library.
I also added a little bit to turn the color of the screen red/green/yellow.
if (root != NULL) {
aJsonObject* bgs = aJson.getObjectItem(root, "bgs");
if (bgs != NULL) {
aJsonObject* def = aJson.getArrayItem(bgs, 0);
if (def != NULL) {
aJsonObject* sgv = aJson.getObjectItem(def, "sgv");
String bg = sgv->valuestring;
int bgInt = bg.toInt();
if (bgInt > 180) lcd.setRGB(255, 0, 0);
if (bgInt > 150 && bgInt <= 180) lcd.setRGB(255, 255, 0);
if (bgInt <= 150) lcd.setRGB(0, 255, 0);
lcd.clear();
lcd.setCursor(0, 0);
lcd.print("Glucose (mg/dl)");
lcd.setCursor(0, 1);
lcd.print(bg);
} I also created some custom characters to show trends, based on a string (pretending to be an enum) that comes back from the JSON service. For example, an up arrow:
byte SingleUp[8] = {
B00000,
B00100,
B01110,
B10101,
B00100,
B00100,
B00100,
B00000
}; All the questionable code is up at https://github.com/shanselman/NightscoutArduinoPlayground
At this point I'm confused/learning about a few things:
- It runs for a while and then stops.
- I don't know what state it's in.
- I would like it to call out to the web service every 5 min and update the LCD. I suspect I am not managing Wi-Fi connection state correctly (as in, not at all).
- So the question is, how does one take a working prototype and turn it into a real appliance that can run forever?
- I'm reusing the stringBuffer which is a bad idea. I need to clear it out.
- Sometimes the Custom Characters are corrupted on the screen.
- No idea why. It works 8 out of 10 times. Perhaps it's an Edison bug or a SeeedStudio bug.
When I get it working reliably, I'd like to 3D Print a case and mount it somewhere. :)
Arduino for Visual Studio
One other thing I found out, there's a fantastic add-in for Visual Studio that will give you a great Arduino Development Environment inside of Visual Studio. It includes simple debugging, breakpoints, a nice serial monitor and more. I'm still finding debugging to be challenging as local watches and step over isn't supported, but it's vastly superior to the tiny Arduino IDE.
Arduino Emulator
Don't have an Arduino or a breadboard? Check out http://123d.circuits.io online. It's amazing. It's an Arduino Circuit Simulator online. Check this out!
You can setup boards, write code, and practice in software before you test it out on hardware.
Don't forget, visit http://marchisformakers.com, tell your friends and tweet us at #MarchIsForMakers!
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