First steps with LoRa Radio Node (Arduino)

The LoRa Radio Node is an AVR Arduino board with a RFM95 LoRa module. This all-in-one LoRa module allows to have a LoRaWan device for a reasonable price around 15€. You need to add a battery (like a LS14500 3,7V battery) on the battery holder for a 4€ extra cost to make it mobile. LiPo option are also available using the power connector. Even if the connectors are looking like grove, they are not compatible so you will have to make your own wiring to connect extensions.

This post is reviewing how to getting started with this board to fire your first LoRaWan frame over The Things Network.

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miniVNA Tiny Plus review

I’ve got my miniVNA Tiny+ this summer and start making test with it. A VNA is a Vector Network Analyzer. Behind this dark name, this is a tool able to analyze the radio response of your circuit and ensure your circuit is tuned to the right frequency. From the data measured by this tool you can find the right adaptation circuit to match your central frequency.

For more information about RF circuit matching, you can read this other post.

The miniVNA Tiny+ is a low cost VNA solution less than 300€ covering frequencies from 1MHz to 3Ghz. These frequencies are good for most of IoT need : LPWAN around 868MHz and Bluetooth at 2,4GHz. The steps are 10Hz for a large precision. With two ports you can measure S11 – power transmitted and received over the same port – and S21 – power transmitted from port 1 and received over port 2.

The miniVNA Tiny+ is an usb solution working with a computer connected to and a software running on the computer. The software is based on Java and may support different Operating Systems.

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Get start with the SigRPI Shield

Raspberry PI Shiel Hat standard

Raspberry PI Shiel Hat standard

The SigRPI shield is a HAT standard board providing SigFox connectivity to your Raspberry PI. As it is not certified for this network it can’t be used in production for this usage, but you can use it as a long range RF that does not need certification. I will later details this with a project related to this function.

By-the-way, the purpose of this board is to let you play easily with sigfox. The raspberry-pi offering a really efficient way to code and to make prototypes.

The shield comes with TD1204 (including accelerometer & GPS) of TD1208 (sigfox modem). You can use it with the standard firmware or upload your own one.

The shield can be ordered in the shop section : here

This posts details how to setup it and use it.

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Sigfox Rf test first experience

This morning, some colleagues helped me to test the rf performance of one of my sigfox tracker. I’m really not an RF expert, I try to improve but there still be a long way to go…

In this design I’m using a TD1204 and a Wurth smd 868 antenna ; I have a 100 ohm impedance net between both (sure it is bad) and LC circuit (that sound not to be the good one – btw).

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Design a 50 ohm impedance microstrip line for RF signals

For RF signal you must draw a 50 ohm net between chip and antenna to get the best performance.This post is the result of my web research on this topic …

There are two ways to design your emitter to antenna solution:

  • A microstrip line : basically you have a net on the top driving the signal and a ground plane on the PCB bottom

microstrip line

  • A coplanar wave guide : your signal is drive by a PCB net on top with two ground plane area on its left & right. If you also have a ground plane on the bottom it’s a grounded coplanar wave guide

The way to get a 50 ohm communication way is different depending on your choice.

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Do you know sigfox ?

SigFox is a French radio frequency technology allowing a really low cost data transfer from Machine to Machine. Compared to GSM, this solution have some great advantages : it costs only 10-16€ per year and the energy consumption is about 1000 time less. For sure there is some constraint and the main one is the quantity of information you can transmit. In fact you have a limit of 150 sent messages / days with a length of 12Bytes. It’s not big but is it enough for a lot of IoT and M2M applications.

This technology works as a modem you can connect to any platform like Arduino, RaspberryPi. The chips are provided by TelecomDesign from a cost about 15€. The starter kit is about 150€ here.

The great advantage of this technology, in a operator point of view is the low density of the architecture where you need only 1000 antennas to cover a territory like France. As a consequence, at this time, already 90% of the country is covered by this technology.