Building a TTN gateway

Following a Things Network meeting in my hometown, I decided to try and move things forward by donating a Raspberry Pi / IMST 880A - based gateway to the guys from Zuid-West TV . They have access to a number of high locations in the area, and are currently building a nice metal cabinet with an internal power supply, which will then be installed on top of one of the highest buildings in Bergen op Zoom. More on that later!
However, in the meantime my original TTN gateway in Roosendaal had suddenly gone very quiet. As it turns out, the gateway range is suddenly limited to about 10 meters! Clearly something is amiss here? It seems that the internal RF receiver has given up, something that cannot be easily repaired and needs to be looked at by the Things Network team.
As there is no way to predict how long this will take, I've quickly built myself a new gateway, based on the proven Raspberry Pi and IMST IC880A board...

A quick 'n dirty gateway build!

So here's what you need to build yourself a multichannel gateway:

The main parts shown in the picture are a Raspberry Pi 2, the IMST IC880A concentrator board, an adapter board to connect the two, and a small housing to put the gateway into. Quite easy, no? Well, that depends on how fancy you want your gateway to be. I just needed it to be simple and reliable, so here's what I did:

1: Put the concentrator and adapter board together

I wanted my gateway to be as compact as possible, so I've soldered the concentrator directly onto the adapter board. I also cut off the original micro-usb connector from the adapter, because it would not fit in my compact housing. However, the adapter also comes with headers which can be used to plug in the concentrator so it is removable.

2: Connect the adapter to the Raspberry Pi

My housing has slots to hold a pcb board, so I've cut a blank board to size and mounted the gateway on it using 5mm plastic spacers. This way no screws are visible from the outside, which is a bonus :)

3: Slide the gateway assembly in the slots

4: Add power supply connections

 Although it is possible to connect the power supply directly, I much prefer to use a proper power connector. I also added an LED, and made a cutout for the network connector, which makes it look like this:

Wiring power to the board was done by connecting power directly to pins 21 (+VDD) and 22 (GND) of the concentrator board. The adapter will then also power the Raspberry Pi, keeping the number of wires to a minimum.

 5: Put it all together

The other end has the SMA connector, which connects to the IMST board. Removing this end will also allow access to the SD card:

The end result looks like this!

Installing software and registering the gateway

Now that the gateway is finished, you will need to install and configure the whole thing of course. Instead of describing this whole process, I'm going to be lazy and refer you to the excellent walk-through put together by the Things Network Zurich group:

From zero to LoRaWAN in a weekend

They've done a very good job in describing the whole installation, which will result in a fully functional gateway. Great work guys!

Parts list

IMST IC880A concentrator board
Raspberry Pi (preferably v2, but v3 will also work)
Adapter board (I used the one from Hackables.cc)
U.Fl to SMA pigtail
5V / 2A adapter (I used a Raspberry Pi adapter)
A suitable housing (mine is a Hammond 1455K1202)
Power connectors
Some nuts, bolts and spacers (depends on the housing used)

Building an outdoor TTN gateway GPA antenna

After playing around with a number of TTN nodes, we quickly discovered that having an indoor antenna on the gateway is not ideal. An outdoor antenna should yield far better results, especially because I do have access to my own rooftop which is about 11 meters high. Commercially available high quality antennas are quite expensive however, so it had to be something simple and DIY.

The DIY way

Luckily for me, several articles have been published already on building TTN antennas. The 868Mhz frequency also means that small and cheap antennas can be built without the need for special or exotic materials. The DIY GPA design described by Lex Bolkesteijn on The Things Network seemed like an excellent starting point, with clear instructions and a good amount of pictures:

Simple outdoor 868Mhz GPA antenna by Lex Bolkesteijn

So, after a visit to a couple of local parts shops I ended up with this:

The steps below describe the building process. As you can see, I tried to make this GPA antenna as weatherproof as possible, even though it is just an experiment. It will probably turn out to be the first of a long line of antenna experiments, but as long as it is on my roof it will need to be able to function in all kinds of weather so why not be thorough?

First, put together the GPA following the instructions in the original article:

 

Then, cut the antenna to the correct size and attach the N-type connector:

 

The result looks something like this:

Last step: put the new antenna up on the roof.

I opted for a wall-mounted bracket so the whole thing would be easily accessible. The DIY GPA now looks like this, about 12 meters high:

Results

So far, so good! The gateway sure seems to pick up a lot more traffic with the new outdoor antenna, although how much of this effect can actually be contributed to the GPA design remains a guess, as just putting the antenna outside will have had a positive effect also. Next step is of course to build a different design (probably a co-linear) and compare. Stay tuned!

Parts list

Antenna:
2mm copper wire (50cm is enough)
crimp-type eyelets (4x)
PVC end caps and tubing (available at the local DIY shop)
3mm x16 screws and nuts (4x)
4mm x13 screws (4x)
N-connector chassis mount
N-connector for Aircell-7 cable
SMA-connector for Aircell-7 cable
Aircell-7 cable (keep this as short as possible!)

Installation:
Wall mount (I used a satellite dish mount)
Clamps (2x)
Galvanized pipe (I used 28mm central heating pipe)
8mm Screws and plugs (4x)

I was able to build the entire antenna for around 65 Euros. Keep in mind however that the installation materials, cable and connectors were much more expensive than the actual antenna...

The STM32 LoRa Discovery kit: adding sensors

(Playing with the X-NUCLEO-IKS01A2)

So, now that the STM32 board is up and running, it's time to start doing something with it. Luckily for me, the friendly folks at the STMicro stand also put a sensor expansion board in my hands. This X-NUCLEO-IKS01A2 board (what's in a name) carries a number of sensors, as well as extension connectors and such:

Key Features (taken from the STMicro website)

• LSM6DSL MEMS 3D accelerometer (±2/±4/±8/±16 g) and 3D gyroscope (±125/±245/±500/±1000/±2000 dps)
• LSM303AGR MEMS 3D accelerometer (±2/±4/±8/±16 g) and MEMS3D magnetometer (±50 gauss)
• LPS22HB MEMS pressure sensor, 260-1260 hPa absolute digital output barometer
• HTS221: capacitive digital relative humidity and temperature
• DIL24 socket for additional MEMS adapters and other sensors
• Free comprehensive development firmware library and example for all sensors compatible with STM32Cube firmware
• I²C sensor hub features on LSM6DSL available
• Compatible with STM32 Nucleo boards
• Equipped with Arduino UNO R3 connector
• RoHS compliant 

The board communicates through I2C and libraries can of course be downloaded from the website.

Let's send some data!

 As with the LRWAN1 board, it really pays off to read at least part of the documentation included in the library. After setting up I2C and configuring the library to use the correct addresses, it is pretty easy to create a compact payload for LoRa transmission:

BSP_sensor_Read( &sensor_data );

temperature  = ( int16_t )( sensor_data.temperature * 100 );
pressure     = ( uint16_t )( sensor_data.pressure * 100 / 10 );
humidity     = ( uint8_t )( sensor_data.humidity );
batteryLevel = ( uint8_t )(HW_GetBatteryLevelInMilliVolts( ) / 100);
lightLevel   = ( uint8_t )(HW_GetLightLevelRaw( ));
soundLevel   = ( uint8_t )(HW_GetSoundLevelRaw( ));

(Full source code available on request)

The lightLevel and soundLevel values are not taken from the included sensors. Because the NUCLEO boards include Arduino-style headers, I decided to stick an Arduino breadboard on top, and included (analog) sensors for sound and light, which are read by two ADC channels. So now the whole contraption looks like this:

Now to find a use for the remaining accelerometer sensors... Any ideas? Please let me know!

Getting started with the STM32 LoRa Discovery Kit

After having done a number of embedded projects using the Microchip processors and development stack, I figured it was about time to try something else for a change. Fortunately I was able to attend the first TheThingsNetwork developer conference in the Netherlands, where I was given an ST Microelectronics B-L072Z-LRWAN1 Discovery board. This board contains everything you need to get started in the world of LoraWAN. The STMicro site lists the following specs:

Key Features

• CMWX1ZZABZ-091 LoRa^® module (Murata)
  • Embedded ultra-low-power STM32L072CZ Series MCUs, based on ARM^® Cortex^® -M0+ core, with 192 Kbytes of Flash memory, 20 Kbytes of RAM, 20 Kbytes of EEPROM
  • USB 2.0 FS
  • 4-channel,12-bit ADC, 2xDAC
  • 6-bit timers, LP-UART, I² C and SPI
  • Embedded SX1276 transceiver
  • LoRa^® , FSK, GFSK, MSK, GMSK and OOK modulations
  • +14 dBm or +20 dBm selectable output power
  • 157 dB maximum link budget
  • Programmable bit rate up to 300 Kbit/s
  • High sensitivity: down to -137 dBm
  • Bullet-proof front end: IIP3 = -12.5 dBm
  • 89 dB blocking immunity
  • Low RX current of 10 mA, 200 nA register retention
  • Fully integrated synthesizer with a resolution of 61 Hz
  • Built-in bit synchronizer for clock recovery
  • Sync word recognition
  • Preamble detection
  • 127 dB+ dynamic range RSSI
• SMA and U.FL RF interface connectors
• Including 50 Ohm SMA RF antenna
• On-board ST-LINK/V2-1 supporting USB re-enumeration capability
• USB ST-LINK functions:
• Board power supply:
  • Through USB bus or external V_IN /3.3 V supply voltage or batteries
• 3xAAA-type-battery holder for standalone operation
• 7 LEDs:
  • 4 general-purpose LEDs
  • A 5 V-power LED
  • An ST-LINK-communication LED
  • A fault-power LED
• 2 push-buttons (user and reset)
• Arduino^™ Uno V3 connectors
• ARM^® mbed^™ (see http://mbed.org

 Nice! Sounds like the perfect opportunity to start in the world of STMicro ARM processors (More info can be found on the STMicro website).

So now: how to get it to work? Although there were several workshops on this subject during the conference, there weren't many people that actually got the board to work and connect. The instructors did their best, but the STMicro development stack just isn't as straightforward to install and set up as Arduino's. Each workshop left us struggling with a multitude of drivers to install, accounts to set up and a confusing number of choices on Development tools. A quick Google search revealed that we were not alone in this; countless discussions on forums are describing the same experience. Once home, I decided to take some time to find out what actually needs to be done to get the board to work and do a small tutorial, so here it is!

Prerequisites

 

For this writeup I am going to assume that you already have a TheThingsNetwork account, and are familiar with LoraWAN. If not, please go to the TheThingsNetwork website and create an account (it's free), and read up on LoraWAN and TTN (This link is a good start).
Before downloading from the links below, you will also need to create an STMicro account (Click here). You will need it to access the downloads on their website.

What to get?

 

STLink driver
The Discovery board comes with a built-in ST-LINK programmer / debugger, for which you will need a driver. This can be downloaded here. Please install this FIRST, before plugging in the Discovery board.

I-CUBE-LRWAN (LoRaWAN software expansion for STM32Cube)
This package contains all libraries and demo projects. It can be downloaded here.

KEIL MDK
In this tutorial I've decided to use the Keil MDK IDE. You can download it here. Please take the time to create an account and register your version of MDK (it's free for STM32F0 and STM32L0 series processors). You will need to have a license in place to be able to successfully build the demo application.

Putting it all together

 

Set up communications
Once the driver is installed, you should be able to start communicating with the Discovery board. The board comes pre-loaded with firmware which will send the DevEUI, AppEUI andAppKey over a serial connection. So, let's make this happen!
First, Connect the board and then open your Device Manager. Your board should be listed in the ports list:

On my system the board COM port is COM5. Open a serial monitor program (I used the serial monitor in the Arduino IDE) and select COM5. Now press the Reset button on the board and something like this will appear:

Register your device

Now go to console.thethingsnetwork.org and register your device on the TTN. Never done this before? Not to worry; TheThingsNetwork has an excellent tutorial right here.

The DEVEui will need to be entered during registration; the AppEui and AppKey will be generated during device registration. These we will need to enter in our project.

Enter the keys in your Project
Now it's time to open the demo Project in Keil MDK. Start the program and open the demo project (Project -> Open Project...) located in the I-CUBE package you have downloaded. There is a separate demo project for each Discovery board and tools stack, which leads to a quite complicated directory structure. This is what it should look like:

ICUBEDIR\Projects\Multi\Applications\LoRa\End_Node\MDK-ARM\B-L072Z-LRWAN1

Load the project file and build it to make sure that all components are OK.
Now it's time to enter the keys. This needs to be done in the file commissioning.h, which is located in the directory Lora\End_Node_inc:

Open the file in MDK and enter the AppEui and AppKey. Do not alter the DevEui; this is not used in OTAA activation. Save the file.

Build the Project and update the Discovery board
Now Rebuild the Project. If the build is successful, you will be able to load the generated firmware into the Discovery board. Use menu Flash -> Download to update the firmware in your device and then press the Reset button on the board.

Done!
The serial monitor should now list something like this:

That's it! Your device is now joined and will start sending data to the TTN network. You can of course monitor this in the TTN console.

Next steps?

 

Getting the device to work is only the first step of course. You will now need to take it further by adding sensors and modifying the code to make it do what you have in mind. Good luck, and please leave feedback below if you found this tutorial useful!