Let’s play with NiMh battery

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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LoRaWAN is coming !

Lora-300x171Last week, Objenious (a bouygues Telecom company) has announced the availability of its LoRaWAN network in France. With already 32 cities covered, about 50% of people can access to the low power network. More over they have announced the deployment of 4000 antennas by end of the year to cover the whole country.

I had the opportunity to test the network and as far as now, I can say it works well, the backend is nice even if it sounds a bit not intuitive yet but for sure they will fix it soon. The good news was a communication about price, with a range of 12€ to 1€ depending on volume, the pricing is really near Sigfox one in a first look. The volume scale will be really important to see the difference as the technical offer (message limit, bandwidth, downlink limit if we have some or not).

In my point of view, Orange is the one loosing most with this announce as they are supposed to start soon with 11 cities in France and they did not yet communicate on the scaling. So now, we are waiting for Orange response and offer in this competition.

The surprising thing in the Objenious announced was the roaming capability with USA as the LoRa frequencies are not compatible between Europe and USA. As most of the device are not yet dual band and the question of detecting the location before emitting still an issue for such use-case, I do not really see how it can have a short term positive impact on project. By-the-way, I was also not aware the LoRaWAN specification for roaming was published. Is it ?

So welcome to Objenious in LPWAN french market, competition is always a good think, and what you announced sounds good and useful for object maker like me.

 

RN2483 downlink considerations

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

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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Devoxx 2016 – IoT talk about

During last Devoxx in Paris, I made a talk about IoT and Sigfox with my friend Daniel. Here is the talk (in french).

 

Make your IoT design on Sigfox or LoRa ?

LoravsSigfoxOnce you have found the great idea of the year and you want to start implementing your first prototype it is time to choose the right technology. Some would say you should not choose at this step and implement both at end but in my point of view it looks like and economical mistake to do this way. Prototype is to demonstrate and final product. It can request another technology, for sure. But in my point of view the best is to take the right one at the beginning. For most LoRa and Sigfox are both equivalent or for some others one is over the other one, best depends who you ask. In my point of view, if I consider my 2-3 years sigfox experience and my starting experience on LoRa with 1 year background research on it, there is no magic answer. Context of your idea is the keypoint then you have some technical elements to take into account to finalize your decision.

This post will try to illustrate where each of the technology is the best and give you some decision keypoints.

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Cheap TFT / LCD touch screen for RaspberryPi with Jessy

TFT screen on a raspberryPi

TFT screen on a raspberryPi

This week I had to play with some TFT screen for RapberryPi for making a prototype for a local company. You can find many TFT screen on Internet but most of them are not coming with a nice fresh documentation for being use and it is kickly a mess to get it start with them. I ordered different one having the same 3.2” size matching my need and got 2 of them for starting tests.

This post details how to use a such screen for displaying a picture on it from a console line.

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Measure waveform duration with EFM32 / TD1208

tim10Measuring a pulse duration in a pulse train was my last week headache with the TD1208 and the not so well documented EFM32. Basically, my objective was to activate a timer on a pulse train to measure the duration of the pulse. This duration was measured about 100uS and occurred at 1 Hz.

My choice was to rise an interrupt on each signal front (raising and falling) and measure the duration between the two first interrupt call. Some reset function ensure we are measuring the low state duration (100uS) not the high state duration (1s). This part will not be described here.  The purpose of this post is to describe the main hole I fallen in.

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