Category Archives: Technology

Tips and test on technological product and components. Operating system, networks, hardware, security…
Astuces et tests autour de produits et composants technologiques, systèmes, réseaux, hardware, sécurité …

SigFox (LoRa) and antenna design

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antenaToday Sigfox is releasing a really good document about antenna design. This pretty document can be found following this link (available on July 7th). This document from TI also contains really well detailed information about the alchemy of antennas and the different kind of product you can find. From Silicon Labs you also have an interesting development kit for 868 antennas with performance published in this application note.

This is to say antenna is one of the most important part of a 868 object, as for Sigfox as for LoRa where the problem is basically the same. I discussed with different sigfox object designed and every-time the antenna was a big project issue. Some has payed about 10-15k€ to get a custom optimized design.

I never experiment a custom design but I made test with various antennas and the purpose of this post will be to give you my feedback on the different solutions.

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3d printing – resize an object with different factor on axes

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openscadTo tell you the full story, I was working on a 3d object I want to reproduce. The initial model is a 10cm object. I’ve got a 3D scan of this object and now I want to make a mold to reproduce it with a smaller size (3cm). All should be simple as even my printer software have a resize option.

The problem started when once resized the height of the object has became too small and the precision of the printer does not allow to have a good result. For my need it was not really important to preserve proportion on the Z axis. So I was looking for a tool able to resize an object with a different setting factor for each of the axis.

This tool exists and more over it is really useful for any STL manipulation (at least you need to be a coder) : its name is OpenSCAD. This tool is a programming language for 3D object allowing different object transformation and creation.

For my need to scale X & Y with a 0.4 factor and Z with a 0.6 factor, the following code was the solution :

scale([0.4, 0.4, 0.6]) import("Moule.stl", convexity=3);

You then just have to export as STL by clicking on STL icon and you have the result. Sounds nice, isn’t it ?!?

How it burns in my car

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Arduino Temperature SensorI make a post on measuring temperature with different sensors and an objective : watch the impact of designing a correct box for you IoT you want to put in a Car.

When sun is lighting your windshield it is not a surprise to get high temperature, but did you expect to get up to 90°C when the outside temperature is about 35°C ?

The packaging have a big impact on temperature as this post will detail it.

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LoRa Wan in a rural environment

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Lora-300x171After making LoRaWan test in a city environment, I make some test in a rural environment with the objective of evaluating the capability for being used in connected farming environment.

The result is really like what we have got in a city, eventually better in a way as the antenna position was on altitude. The following map makes with 6kbps communication shows the coverage. You can see that the coverage is really limited on the Eastern direction. This is due to higher mountains this way. Mountain are the main limiting elements and as you can see, even on short distance communication they are blocking any signal.

Read more to access the map.

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Measure and store multiple temperature with Arduino

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Arduino Temperature SensorFor a certain IoT design I had to understand how my box design impacts the temperature of the circuit and of my battery. To understand how it works in the real environment, I made a small circuit based on an Arduino Nano to get temperature with 6 different sensors and store it in a flash memory for later use.

This post describes the way to do this multi-temperature sensor platform. Code is under GPL.

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Let’s play with NiMh battery

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NiMh batteries

NiMh batteries

After writing a post about my experience with LiPo Batteries I’m now proposing a post about NiMh. LiPos are good batteries : not expensive with a good energy density, really easy to manage for charging. For these reason they are used in many electronic designs.

But in some applications they are not enough stable, this is as an example the case for an automotive use where the internal temperature of a car can reach higher temperature than 65°C. This is the limit for LiPos. In my experiences I had some having been destroyed due to warm temperature.

NiMh is not an optimal solution but you can find some batteries capable to support 85°C and resist to +130°C before being destroyed and have a fire risk. Varta V500HT is a good example of battery for a such use.

NiMh is less easy to use than LiPos, this post is detailing my experience.

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RN2483 downlink considerations

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Microchip RN2483 Lora

Microchip RN2483 Lora

Making downlink working correctly with RN2483 on LoRaWan is not a simple a quick thing to do if you do not have all the keys to do it. After spending some time to fix my code for this, here are the tips to consider and not forget !

 

 

 

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LoRa experience in a real city environment

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Lora-300x171I was looking for a real LoRaWan experimentation on the field, not only a given open field performance where the result do not match the reality.

For this reason, I installed a Kerlink gateway on a friend’s balcony living on a high part of my city. Then I moved a tracker reporting its GPS position on regular basis and day after day I built a map of the area covered by this antenna.

This post details the results of this expermientation

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