While this project was designed with aquaponics in mind, it does not require an aquaponics system, making it useful in any application that wants graph data online in real-time. The included application, therefore, is bare-bones to make it easier to integrate into your own project.
You can find a background tutorial on the light-dependent-resistor here.
I can think of a multitude of reasons you would want to graph data from an Arduino sensor, but the idea of retrieving the SD card from whatever environment your Arduino is in, hooking it up to a computer, downloading the most recent data and finally loading the data into your favourite visualizer, well that gets old fast. Instead, lets hook the Arduino up to the internet and graph the data in real-time.
This project focuses on collecting the light level from an aquaponics greenhouse using a light dependent resistor (LDR) and sending it to Google App Engine to be graphed using Google Chart Tools. The cycle is as follows: the Arduino attempts to connect to the webapp and waits ten seconds before parsing the response. If the response is 'Ok', a good connection was made and a bicolor LED is set to green. If it could not connect, the LED is set to red. If a good connection was made, the Arduino will read from analog pin zero (A0) and create a GET request to App Engine with the LDR reading. App Engine will save the LDR reading and update the current environment property.
On startup, the client will request the server to query the datastore for the light data and receives a JSON array of the current day's data. The array is parsed and an AJAX request is made to create a table using Chart Tools. Finally, the client sets an interval for a function that requests the last data entry as another JSON array, parses the response, compares it to the last data in the table and adds the data if they are not the same reading, creating a dynamically updated display.
1. Arduino IDE: Arduino-1.0.3
2. App Engine SDK: Python, Linux, 1.7.4
3. Python: Python2.7
4. Ubuntu 12.04
1 x Arduino Uno R3
1 x Arduino Ethernet Shield R3
1 x Arduino Power Cord (optional, but gets better power than just the USB)
1 x Bicolor LED (Red/Green)
1 x 1/4W 470 ohm resistor
1 x 1/4W 10k ohm resistor
1 x Light Dependent Resistor
Breadboard jumper wires
Step 1 - Create a new App on App Engine
Since all of our internet based projects use App Engine, we've created an independent tutorial to explain how to create a new app.
- Create a new app.
Step 2 - GAE Project Code
- Download the project code here.
- Extract the tar file in your home directory. It will be labelled IAquaponics_LDR. Inside you will find the App Engine directory called myapsystem and the Arduino folder arduino.
- The name of the GAE code is irrelevant, but you can rename it if you wish. The rest of the instructions in this tutorial will use the original name. If you choose to amend the directions accordingly.
- Inside myapsystem you will find app.yaml. Open that in your favourite text editor and edit the first line to the project name you created in Step 1; see Figure 1.
|Fig 1. Edit the highlighted text.|
- Take note of the bottom. The main page of our webapp is listed last because it will catch all url requests not listed above it. In fact, this webapp only has two pages: adacs and main. The former is used by the Arduino and the latter is the visible interface you will see with the web browser (client).
- Finally, under main.app, you will see login: admin. This app uses Google Accounts as you saw in Step 1, but we are restricting application to the webapp to just you.
Step 3 - Launch the AppEngine SDK with Your Project
- Open a terminal and launch the AppEngine SDK and your project.
python2.7 AppEngine/dev_appserver.py IAquaponics_LDR/myapsystem
- If you were successful, the terminal will tell you the project is located at
- So fire up a web browser and point it to that url. Because we have restricted access to admin, you will need to login as admin. The login name is irrelevant, but you will need to stay consistent in the login name you choose. Beneath the email input box you need to check the box that says "Sign in as Administrator" - see Figure 2. Then login.
|Fig 2. Login as Administrator.|
- At this point you should see Figure 3.
|Fig 3. Main screen.|
- There are two important things to note. First, the chart was built with a piece of data. If you hover around the point (Now, 750), you will highlight the data. If you wait 20 seconds, that will disappear.
- More importantly you will see a text box to input your timezone offset from UTC. To get accurate timestamps of your readings from the Arduino, you'll need your timezone before you hook up the Arduino. In Iowa, we are six (6) hours behind, so we would submit
- Australia is eight hours ahead of UTC, so they input
- Next, we are going to replicate a call the Arduino will make to the server. In the browser's url bar, type
- You'll be presented with a page that says 'Ok'. Now go back using the Back button and you'll see a seemingly blank chart, like Figure 4.
|Fig 4. First data.|
- It's actually not blank. You can see the timestamp on the bottom of the chart and you can hover above (timestamp, 800) and see your data input.
Step 4 - Go Live: Upload Your Project to App Engine
- If everything has worked for you so far, it's time to upload the webapp to the live server. In a terminal, from your home directory, type
./appcfg.py update ~/IAquaponics_LDR/myapsystem
- You will be prompted to input your Google email and password you used to create the project from Step 1.
- When the update is complete, go to your webapp.
- If you are not already logged into your Google account, you'll be prompted to. Note the login is consistent for all of Google's products.
- Once you are logged in, you should see the same screen from the SDK. Again, input your time zone offset.
- To test the live webapp, replicate the Arduino call just as you did in Step 3.
Step 5 - Arduino
- Wire up your breadboard using the Fritzing diagram in Figure 5. The Arduino is not shown, but obviously it resides under the Ethernet Shield. The 470 ohm resistor is used for the bicolor LED and the 10k resistor is used for the LDR.
|Fig 5. Fritzing Diagram.|
- You can find the Arduino file, LDR.ino inside the arduino folder. Upload that to your IDE.
- There are three places the Arduino code needs to be altered, Figs 6, 7 and 8. Replace the highlighted code with the project name you developed in Step 1.
|Fig 6. First location.|
|Fig 7. Second location.|
|Fig 8. Third and final location.|
- Select the correct Arduino Board from the menu list and make sure to select the proper Serial Port. Save and upload your code to your Uno, then open a serial monitor.
- When the Arduino connects, the bicolor LED will turn green. If there is a connection issue, the Serial output will tell you and the LED will turn red (see Note 1).
- Once the Arduino connects and sends data, go back to your web browser look at your app home page. You should see the graph update itself as it receives data from the datastore. Figure 9 shows the our graph over a very short period of time. The large dip at 19:23:34 was due to our hand blocking the LDR from the light source.
|Fig 9. Real-time data graph.|
- And that's it.
- Since working with AppEngine and Arduino Ethernet we have encountered one consistent error. The Arduino will report that it failed to make the third request. The first two are fine. Every request after the third connects and works, but for some reason the third one will fail, every time and we don't know if it is due to App Engine or the Arduino.
- For troubleshooting and development mode, Serial output is on. Specifically, there are two counters provided, which need to be commented out (using double slashes at the beginning of the line: //). If you don't, the counter can grow very, very large.
You are free to modify the code as you see fit, but I have one suggestion. Google App Engine allows for daily free quotas, if you exceed the free quotas and don't pay a monthly fee ($9), your app will be shut down. Two free quotas you should be aware of are instance hours and read/write/small operations on the datastore. You get 28 free instance hours, reset daily. The Arduino should not be set to send requests to AppEngine too often, or new instances of your app may spawn. Similarly, the browser is set to refresh every 20 seconds. If you combine the Arduino requests with the client requests, and make them too frequently, you may again spawn new instances. In fact, your app is hosted on a server with other applications. Depending on the load on the other applications, your app may spawn new instances elsewhere. Better safe than sorry.
Read/write operations are set to 50K each and AppEngine is a little funny about how they count these, but needless to say, making a request every ten seconds, all day from both the browser and Arduino will run up a lot of operations. Try not to go below twenty seconds on both the client and Arduino and enjoy the free quota.
If you have trouble, hit up the comments below. And if you include this in one of your own projects, send us a screenshot, we'd love to see it.
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