Log data with SDI-12 USB adapter
June 26, 2016 Leave a comment
On my last post, I showed a couple of videos of how to connect an SDI-12 sensor to the SDI-12 USB adapter. Here is a video of how to configure an SDI-12 sensor and log data with the adapter:
Sorry there was some noise in the background that I couldn’t get rid off with the authoring software. Here is the transcript in case you need it. I will explain how to send data to sparkfun’s data server in my next post.
Let’s plug in the SDI-12 USB adapter. Windows will automatically install its driver and create a COM port, in this case, COM18. If this is your first time installing a COM port on your computer, you will need to be patient.
What we are looking at are two windows. The window on the left is the python shell. It shows you the input and output of python scripts. The window on the right side is the SDI-12 configuration script version 1.1. We run this script to set up the sensor’s SDI-12 address.
On the left window, you can see the messages printed by the configuration script in blue. This script runs on windows, mac, linux, and raspberry pi.
The script has discovered a number of COM ports and listed them all on the left window. The first one, item zero, is our SDI-12 USB adapter, i.e. COM18. Type zero and enter. Ignore the rest. If you are unsure about the COM port number, run this script with the adapter disconnected and then run it again with the adapter connected. This way you can see which port belongs to the adapter.
After a short moment, the script has detected the SDI-12 sensor at address 1. The information printed out indicates sensor address 1, compliant with SDI-12 standard version 1.3, and the manufacturer is Decagon. The sensor is a spectral reflectance sensor and its serial number is also printed out.
What this script does is to detect the one-character SDI-12 sensor address, print out the sensor information, and allows you to change its SDI-12 sensor address. Valid address includes 0-9, A-Z, and a-z.
Let’s set the sensor address to 2. To check that this has taken effect, we run the script again.
Now it has detected the new address. The address is saved on the sensor until it is changed again.
Now let’s look at the data logger script.
What this script does is: it logs data to two places, a file on the computer, and it also sends the same data to a server at sparkfun electronics. Everyone that runs this sample data logging script shares the same storage on the server and can see results from everyone else. You can also create your own storage or stream on sparkfun so you can keep the data to yourself.
Here I have python shell and sdi_12_logger script version 1.1. Let’s run the script with F5. This time there is a longer printout and it does say it runs on Mac OSX.
Next we see a list of serial ports. We select zero for COM18, like before.
Then we are required to enter the total number of data points. Let’s try 5. You can enter any large number of data points and stop the data acquisition anytime with Ctrl-C. Data saved on your computer and sent to the server will not be lost if you stop the script.
Delay between data points is specified in seconds. We’ll use 10 seconds. Then we decide whether to store each data point with local or universal time. Enter 1 to pick local time.
Enter the SDI-12 sensor address, 2.
Here is the first data point. Date and time, then two spectral reflectance values, and then 2.0 for facing upward.
The curl command that appears on the next line will only appear if you have curl installed, which is a tool to send HTTP requests. So besides a local copy of your data, you also have an online copy on sparkfun electronics server.
OK now we finished collecting 5 data points and the python shell prompt has returned.
We will take a look at the data file and the server data next.