In order to test the reception range of a Lora module, we decide to sent a stratospheric balloon. For the occasion, an arduino card with a Lora chip from IMST was created.
The launch was on November 4, 2017 in Payerne, Switzerland with a cloudy weather. This experience was possible in the context of my work at BCD microtechnique SA
We created a board with an Atmel MEGA 328p processor and a LoRa iM880B-L chip from IMST. We added temperature probes and a GPS to retrieve the balloon. The Lora was configured with 16dbm power.
Unfortunately the GPS did not work properly. From 500m relative altitude, he lost the signal. We have no answer for the moment why he lost the signal. One hypothesis is that the antenna was not sensitive enough and that at altitude it is disturbed. However, we tested it using a drone mounted at 500m and everything worked properly. For the next flight, we will change GPS with a bigger one.
We mounted the module in a box made with 3D printing. A second traditional module operating on the amateur radio waves was put to follow up. Finally a wide angle camera with a sunscreen was installed. Everything was put in a capsule in sagex.
Throughout the flight, the Lora module was received by several gateways of the TTN community. It is possible to see them on the map running on my server
If a gateway owner recognizes its location, do not hesitate to share it in the forum.
The predictions given by Meteo Switzerland gave a landing near Zurich.
The ball finally finished its race a little above Zurich in the middle of a grove at the top of a tree at 30m ... With the drone, we can better see the ball at the top of his tree.
Catch the balloon
On the day of the launch, I moved on the spot for the recovered, but as it was hanging at the top of the tree I could not do anything. During two weeks, we looked for several solutions to get it without having to cut the tree. My parents in the area took the opportunity to see if the ball had not come down alone with the help of strong winds that occurred during the two weeks. Luckily, this was the case. They were able to bring it back to me and I was able to recover the material as well as the video.
At 30km we really have a beautiful view.
Let's talk about the results. As said before, the GPS did not function but we still communicated continuously during the flight. The balloon communicated with part of Europe and to the Netherlands about 600km.
Shortly before throwing the ball, a team from Germany performed a similar experiment and got a better result. They managed to communicate more than 700km.
I was a little disappointed when I read their article shortly before sending my balloon. I thought I would be the first to send a lora module into the stratosphere.
With the capsule, we put temperature sensors that we can see below. At the highest height, the capsule was lowered to about -50 ° C. The yellow curve represents the temperature inside the capsule and the red on the outside.
The code behind
Of course, I use the network "The Things Netowk" to receive LoRa messages. These are transferred to my server via HTTP.
My server is a virtual machine running Debian with Node-Red in the clouds. From this interface, I save the messages in a MySQL database. I record every message and gateway I receive in the JSON message. I have a little logic not to register gateways double which requires me to have 3 tables for registration. The first contains the message with the linked data. The second table lists the gateways. The last one records a list that links each message to each gatway by saving the linked data. (RSSI, SNR)
The page presenting the gateways that have captured will directly search the information in the database via Ajax commands. For viewing, I use the Google Maps API which is really easy to use.
I do not really have a published code, node-red does a lot of the work. If however, you have questions, do not hesitate to post them in the forum. I would take the time to develop some of it even more in detail.
In the near future, a next launch will be made with a new GPS and other more accurate sensor. Now that we know that communication works well we can put a little more sensors.
If you have questions do not hesitate to write on the forum or to contact me.