Bill of materials

Building a TTN node

Identifying the components

Our bill of materials (set available at TinyTronics)

• RFM Module RFM95W (868 Mhz)

• Pro Mini 3.3V 8Mhz (5V will NOT work!!)

• FT232RL-3.3v-5v-TTL-USB-Serial-Port-Adapter (has to have a 3.3V option!)

• USB cable for FTDI

• 1x Led 3mm red

• 1x resistor 1k (brown-black-red)

• Header 6p female (Arduino programming)

• Header 40p divided in: 2x 4p, 1x 6p, 1x 3p and 1x 2p

• PCB ‘DougLarue’

• Sensor BMP280 (Temperature and air pressure)

• Battery holder 2x AA

• 2 AA batteries

• optional: 2x female headers 2p (battery and led connection)

Low Power the Arduino?

There is an option to ‘low power’ the Arduino. BUT this requires some precise soldering! The setup will work without removing the components. So if you are a novice solderer, skip the first part! It requires a sharp knife to remove the power converter, and to cut the connections for the two on board leds. If you want to battery power your node for a longer time (weeks or more) this is the option for you. Current in sleep mode will be reduced to <100uA. Look at the instructions at the end of this manual

Soldering the module

Setting up the peripherals

Starting up the Arduino Environment

https://www.arduino.cc/en/Guide/HomePage

Install the Arduino IDE on your favourite platform (Mac, Linux or Windows). These examples work only with the latest Arduino IDE (tested on 1.6.9)!

https://www.arduino.cc/en/Guide/ArduinoProMini

Use the FTDI, ensure that the jumper is on the ‘3V’ side. Battery power turned off (check the switch)

Connect the FTDI and the Pro Mini so that the components are both facing up.

• Start the Arduino IDE

• Select the board: ‘Arduino Pro or Pro mini’

• Select the Processor ‘ATmega328 (3.3V, 8Mhz)

• Select the COM port given

Select the default ‘BLINK’ example, change the LED pin from 13 to 2, in the newest blink example you may change ‘LED_BUILTIN’ to 2.

Load the code with CTRL-U to the Pro Mini. After compilation and uploading the led on the board should blink at 1 Hz. Great: we have a working programming environment!

Testing the sensors

1. Add the BMP280 library: Sketch-> include library -> manage libraries:

2. Search for BMP280:

1. Install the library ‘I2C-Sensor-Lib’

2. Connect the BMP280 sensor:

1. Load the  the i2c_BMP280  example (File->Examples->I2C-Sensor-Lib->i2c_BMP280). By opening the Serial Monitor (115200 bps) you will see the height, pressure and temperature of the sensor. Put your finger on the sensor (the small metal unit) and see the temperature rise. The sensor’s height is relative and this library has a ‘fixed’ sea level pressure. (Beyond the scope of this workshop, we do not use the height, but if you want to experiment with it): To change this you have to change the i2c_bmp280.h file. In line 306, 102025 is the actual pressure:

        meter = 44330.0*(1-pow(float(iPascal)/102025.0,1.0/5.255));

The Serial Monitor should display something like this:

Great! Our sensor is working! If it is not: check the I2C bus (SDA <-> SCL) and the two inner pins of the Pro Mini (A4 and A5) these two are the I2C bus! If you forgot to solder these, you can put a piece of wire through the holes and solder it at both sides.

Getting things started on ‘The Things Network’

Download the LMIC library from Github:

1. Goto https://github.com/matthijskooijman/arduino-lmic

2. Choose ‘Clone or download’

3. Download ZIP

4. Mark the location

5. Go to Arduino IDE

6. Select ‘Sketch->Include Library->Add .ZIP Library’

7. Select the downloaded Arduino-lmic-master.zip file from your download location

8. Goto https://github.com/rocketscream/Low-Power

9. Choose ‘Clone or Download’

10. Download ZIP

11. Mark the location

12. Go to Arduino IDE

13. Select ‘Sketch->Include Library->Add .ZIP Library’

14. Select the downloaded low-power-master.zip file from your download location

To help joining OTAA faster (seconds in stat of 7 minutes) you may alter the LMIC library. You can find LMIC.C file in <My Documents>\Arduino\Libraries\Arduino-lmic-master\src\lmic

1. Open the file in your favorite source code browser (or use WordPad)

2. Go to line 684 (or find ‘setDrJoin’ to find the line below)

3. Change     setDrJoin(DRCHG_SET, DR_SF7);  to:     setDrJoin(DRCHG_SET, DR_SF9);

4. Save LMIC.C

The Things Network Dashboard

Your applications and devices can be managed by The Things Network Dashboard.

Create an Account

To use the dashboard, you need a The Things Network account. You can create an account here:

https://account.thethingsnetwork.org/users/login .

After registering and validating your email address, you will be able to log in to The Things Network Dashboard.

Create an Application

https://console.thethingsnetwork.org/applications

Choose ‘add application’

Give your Application a unique ID. You can use ONLY lowercase! You can add an unique number to get uniqueness over the ttn network (this is a global ID)

Your description can be any description you like.

First download the code for ttn_bmp280i.ino from https://github.com/galagaking/ttn_nodeworkshop

You can download the ZIP and unzip the file to get the examples:

1. Goto https://github.com/galagaking/ttn_nodeworkshop

2. Choose ‘Clone or download’

3. Download ZIP

4. Open the ZIP in explorer

5. Open the example ttn_bmp280.ino

6. Create the sketch folder for the application

Register the device

Now register your device.  We will use OTAA in this example. This is ‘Over the Air Authentication’. You have to define an address for yourself. This is a kind of MAC address, but because there is no registration yet of these, define some RANDOM 8 byte value, using your postcode and some values in between.

There are three values you should copy into your Arduino Code. Dev EUI (the device identifier), App EUI (The application identifier) and the App key.

Dev EUI

With the <> sign you can select different ‘views’. We need the ‘LSB’ view, also called little Endian or Least Significant Byte First.
NOTE: For the App Key we need MSB, not LSB.

Both Dev EUI and App EUI will be used in LSB or little Endian format.

First copy the Dev EUI with the clip board sign on the right. Paste the string into your code at the static const u1_t DEVEUI. Remember to respect the semicolon at the end of the line.

APP EUI

Next copy APP EUI, select LSB for this one as well. Copy to APPEUI in your code.

APP KEY

The last key is a secret hash, so this one just shows when you click the ‘EYE’ icon. After that you can copy this to the clipboard. This one can be copied in MSB format.

Copy the 16 bytes APPKEY after static const u1_t APPKEY[16] = .

If things are not working, in most cases LSB and MSB are mixed up. So follow again above instructions and take care of LSB and MSB!!

• The BMP280 sensor should be connected!
• Upload your code to the Arduino.
• The LED will blink during the JOIN process. The Arduino gets his keys from TTN, thereby all information sent will be encrypted with these keys.
  

Payload Function

After a few seconds, the LED will stop blinking. You will see the information coming in into the dashboard. This is coded information, because some algorithm is used to put temperature and humidity in two bytes.

To get the right display format, we can create a decoder in our application. Select your application and open the ‘Payload Functions’:

Enter the function below, overwriting the standard function

function Decoder(bytes, port) {

var mbar = 970+((bytes[1] >> 2) & 0x3F);

var temperature = -2400+6.25*(((bytes[1] & 0x03) << 8) | bytes[0]);

return {

mbar: mbar,

celcius: temperature / 100.0

};

}

First test the function with two dummy bytes CE D0, And then Save the function.

Return to your data and look what happens:

This way you can put several values into a byte string. Sending in clear ASCII is possible but due to bandwidth limitations not preferable in production environments. To make this even more scalable take a look at https://github.com/thesolarnomad/lora-serialization .

DOWNLINK

To send bytes to our node we can use the ‘Downlink’ section: in the console, click on your device and scroll down in the Overview page . Enter one byte (two hex digits, 05 for example) and click Send.

The information will be send to the node after the next time the node contacts the gateway. With a sample rate of approx. 60 seconds, that is the maximum time this data will be received. The Led will blink this amount of times, with a maximum of 10 (0x0A).

Using Activation by Personalization (ABP)

ABP

Activation by Personalization (ABP) is a method where the security keys are stored in the device. Not as safe as the OTAA method, but for experiments it works OK. There is no join procedure, nodes will work right away.

Register the device.

Now edit the settings of the device and choose ABP (OTAA will be selected by default)

Select ‘save’. Now some values are system generated and we have to copy them to our code. We use the ttn_bmp280_abp.ino example here.

• Copy the Device Address as a HEX value to DEVADDR in the example, so 26 01 1A 32 will be 0x26011A32.

• Copy the Network Session Key as MSB to NWSKEY.

• Copy the App Session Key as MSB to APPSKEY.

Compile and upload the code. Check in the dashboard the working.

You might want to uncheck the frame counter check

If the frame counter is checked, you must respect the sequence number, and probably copied packages are refused on the network. Though restarting you node, and thereby resetting the frame counter, will disable your node. So to get this working, you have to disable this check by unchecking this box. You can integrate the code of ttn_bmp280 in the abp example.

Low Power the ProMini (Optional - experienced users only)

These steps require precise soldering and cutting. Experienced users only, you may destroy your ProMini!

Remove the Regulator

The easiest way to remove the regulator and not damage the board is to use a very sharp scalpel to cut through the regulator leads at the point they join the regulator body.

Remove the LEDs

There are two LEDs on the Pro Mini board. The two LEDs are marked with a red square in the following picture. The power LED is marked with an arrow. If you are not sure where the power LED is on your board, then you can just power it and you will see the LED.

When you found the power LED, then try to locate at least one trace that leads to the LED. In the second picture below, I marked the traces on my board. A high-resolution picture with a lot of light helps to find the traces.

When you found a trace to the power LED, then you take a knife and break the trace, so that it will not conduct any more. You can see my result in the third picture below.

Removing the LEDs can be tricky, so it’s easier to remove the series resistors for the LEDs instead. This version of Pro Mini also has a resistor feedback network for the regulator across VCC, these consume power so should be removed. Just push the resistors aside with a soldering iron. The picture shows the Pro Mini with unwanted parts removed, locations of the removed components are circled in red.

More on this subject you may find at: https://andreasrohner.at/posts/Electronics/How-to-modify-an-Arduino-Pro-Mini-clone-for-low-power-consumption/

LMIC PIN mapping

LMIC Pin Mapping

If you are using other ‘LMIC’ or TTN examples, there is ONE part to take care of, the pin setting of the RFM95 module. Most times you have to adjust this to the pinout of the board:

And even more…

• You can add professional Antenna’s on the PCB by using the appropriate connector.

• Support: https://www.thethingsnetwork.org/forum/

Bits and values - Serialization of the data

Using the example code