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JUST DO IoT

BBC Micro:Bit connected to LoRaWAN network

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This project is a proof of concept for some exciting new opportunities to combine the disruptive developments of both the BBC Micro:Bit and The Things Network(TTN). The BBC Micro:Bit puts a programmable IOT device into the hands of over a million new innovators. TTN is an openly usable and deploy-able IOT network supporting low power devices over a range of several kilometers based on LoRaWAN technology. While LoRaWAN has limited bandwidth; the low power, low cost, open access, and a strong support community allows hackers and makers to create working solutions with communicating devices today.

The BBC Micro:Bit is an IOT microprocessor board based on the Nordic Semiconductor NRF51822 chip with an ARM Cortex M0 processor and bluetooth. For this project it was decided to program the board using the micropython development environment.

The LoRaWAN radio module used to connect to the TTN is the RN2483 from Microchip. This module connects to the Micro:Bit over a serial interface. A microcontroller integral to the RN2483 take care of all the processing for the radio and supports the LoRaWAN protocol layers. In this build the RN2483 module is mounted on a breakout board from Azzy's Electronics Store on Tindie.

The Radio module is powered from the Micro:Bit using either USB or battery. Three data lines between the Micro:Bit and radio module carry a hardware reset line and serial transmit and receive data.

The Micro:Bit only has a single serial port and this is redirected to the I/O pins of the board. This means that the python console is no longer available, but does not interfere with the ability to program the Micro:Bit. Unfortunately the bluetooth interface on the Micro:Bit is not available when using python.

The python code initializes the radio over the serial connection and sends data packets over the radio channel. The antenna for the 868 MHz radio in this case is a short piece of wire of the correct length (82mm).

The Things Network (TTN) comprises a number of internet connected LoRaWAN gateways deployed by enthusiastic supporters in a growing number of areas around the world. If you don't already have local coverage, then you can deploy your own gateway and connect it to TTN. While gateways are expensive at around $500 each, many local funding opportunities exist, and exploiting these makes the IOT opportunities more visible and pertinent to the local community.

This project was developed at rLab (Reading Hackspace), where we installed a gateway as part of the Reading TTN network. Our objective was to avoid the corporate competition to define and own the IOT arena, and enable a wider resource of innovators. Reading TTN fit in with our Hackspace "Just Do It" philosophy, hence "JUST DO IoT"

justdoiot.py

Micro:Bit Python Code for RN2483 LoRaWAN module

plain - 1.51 kB - 06/09/2016 at 14:25

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  • LoRaWAN for BBC Micro:Bit Motherboard

    richard.ibbotson08/04/2016 at 10:23 0 comments

    At last I have a LoRaWAN Micro:Bit device which meets my design goals and allows us to move on to investigate and develop uses and applications.Ten prototypes have now been built using PCBs from PCBWay, and are being deployed in useful tasks

    The device is built as a small motherboard for the Micro:Bit.

    The edge connector on the Micro:Bit is rather odd, and I do need more connections than the previous screw connections allowed. Besides the original use of power, serial data and reset, I now want to provide I/O connectors for sensors, and access the I2C bus on the Micro:Bit. Choosing which pins for the I/O connectors is important, and I made a mistake on my first prototype board using pins which provide LED Col drives, because these are sometimes used by the LED array.

    While described as a 22 wayedge connector, it is actually a 40 way double sided 1.27mm pitch edge connector. These are now available at reasonable cost on eBay in both horizontal and vertical mounting.

    The motherboard carries the Microchip RN2483 LoRaWAN radio which still connects to the seraia port of the Micro;Bit. I added an on-board 868MHz antenna which seems to work just as well as the stub antenna I was using before. I used the 0868AT43A0020 ceramic antenna from Johanson Technology.

    For power control I chose to add a separate Real Time Clock (RTC) chip, this gives low power while sleeping and fairly accurate timing. I choose the MCP7940N from Microchip as the RTC because it had an alarm function which I could use for the wakeup.Datasheet

    The RTC connects to the I2C bus of the Micro:Bit. The I2C bus is also used on the Micro:Bit to interface the magnetometer and accelerometer, it is also brought out to a grove connector on the motherboard to allow connection of external I2C sensors.

    A battery pack with two AA size Alkaline Cells was added to the motherboard giving around 2000mAh at a nominal 3V output. The battery power is controlled with a MOSFET circuit which can power off the entire board electronics with the exception of providing backup to the RTC. The board is powered on by a push button, or when the RTC alarm is triggered.

    Two grove sensor connector are mounted on the motherboard, One on the I2C bus, and one providing two general purpose Analog or Digital I/O

    The PCB was designed in Eagle and the files are on my GitHub here: LoRaWAN_MicroBit

    Micropython files have been updated to support the new pin allocations, and the inclusion of functions to control the RTC.

  • Been Doing Iot, but not sharing it, Sorry Folks!

    richard.ibbotson07/31/2016 at 15:32 0 comments

    Ouch, I really didn't think it was so long since my last project log entry. I have been Just IoTing, Just not sharing with people what is happening. So to say sorry, and catch up:

    First, the world has changed a bit. The BBC Micro:Bit is now available from UK distributors. bbc-microbit . Updates to MicroPython include a radio function, which is not Bluetooth, but uses the 2.4GHz radio in the NRF51822 for networking MicroPython Docs.. This might offer opportunities to network over a small area with 2.4GHz, then connect over LoRaWAN for longer distance. It does suggest however, that we will not be getting Bluetooth under MicroPython. I have not investigated opportunities to use C++, or Touch Develop.

    My LoRaWAN network connection is to the Things Network, and that has had an update too Things Network Backend. A new staging back-end has been implemented with a more logical and open structure. Device nodes now use Over the Air Activation (OTAA) to get device addresses, so the network join process has changed. Also the Things network now provides no message storage, so applications need to collect messages from the Things Network using MQTT subscription or node.js, as they occur.

    We held a LoRaWAN workshop at rLab(Reading Hackspace) on July 2nd 2015. This was really valuable to help us understand the changes in the Things Network, and better prepare end to end IoT solutions from device through to application. We updated the Multitech LoRaWAN Gateways, and sucessfully installed an additional LinkLabs Gateway based on the Raspberry Pi.

    So to progress on the Micro:Bit LoRaWAN device node. Following the work to measure power consumption, I built a prototype PCB which contained not only the RN2483, but also an electronic power switch, and a Real Time Clock(RTC) Timer IC. This allowed the whole board except the RTC to be turned off between transmissions. Sleeping power consumption has dropped from 4mA to 1.1uA, meaning devices transmitting infrequently can have now have battery life of over a year. I made some mistakes and poor design choices on the prototype, so made a second run of the PCB with some fixes and improvements.

    The pictures above are of the first prototype, I will do separate log for the new board

  • Reducing Power Consumption

    richard.ibbotson06/16/2016 at 00:02 0 comments

    Power consumption is clearly a major factor for IoT devices. The expectations of battery life for this device is for at least one month (750 hours+) of operation. The battery pack which came with the Micro:Bits is rated at 3V and 1000mAh. This means we have to get current consumption below 1 mA on average.

    The consumers of the power are the Micro:Bit and the RN2483 radio. Initial measurements on the Micro:Bit are immediately not encouraging. Just sleeping, with no LED on has a current consumption of 1.75mA, and turning the LEDs on adds another 9mA. So even with the LED's off and doing nothing, we would drain the batteries in well undre our target of one month. So why is this ? The NRF51822 has great low power operating capability, but there is nothing in Micropython (Yet!) to take advantage of this. We could move to programming in C++ under MBed to get direct control of the NRF51822's power management, but that messes with our "Just do IoT" philosophy for using the basic toolchains provided. The circuit schematic of the Micro:Bit is not published, and it is also not clear how the second ARM M0 processor which does the USB interface is powered. It may be we can fix the NRF51822, but the USB chip while unused on battery power still sucks the juice. Maybe we bit the dirt on this project, or do we need a good hack!

    Let's look at the radio anyways. The specification is a bit more clear here, with quoted values of 2.8mA at idle, 14.2mA on receive, 10uA on sleep, and 38mA on transmit. Some big numbers and a small one. However, the duty cycle of LoRaWAN is 1%, so it appears that the RN2483 could be power managed to meet our target of one month operation.

    I did some measurements of current consumption of the whole Prototype system and on the RN2483 alone, while running the LoRaWAN Micropython program, which confirmed the figures above. The whole system took around 8.5mA at idle, which would maybe drop to around 8mA with the few LED's of the tick turned off. When transmitting the current jumped to around 50mA, but only for around 100mS. When receiving there is a smaller current jump to around 24mA as expected from the specification.

    Looking at the RN2483 alone confirms the datasheet figures with 2.5mA at idle, and 40mA when transmitting. I sent the command to the RN2483 to enter deep sleep mode, and the current plummeted to around 2 uA, until the RN2483 awoke after the set sleep time.

    So where from here ? I really hope the software developers for the Micro:Bit look to a power management strategy, but that will not help me short term. My decision is to add a circuit to turn power off to the device between transmission events.. This will be awoken by the deep sleep mode of the RN2483, or by an external Real Time Clock IC, which can power down the Micro:Bit between transmissions. This also gives the opportunity to make a PCB to hold the RN2483 and an edge connector for the Micro:Bit.

  • Project Log and To Do List

    richard.ibbotson06/09/2016 at 13:21 0 comments

    09/06/16 Start project log here to show progress. Hardware proof of concept complete. Python program written to initialize radio and send data to TTN. Data received and identified from TTN api.

    To Do:

    Work on measuring and managing power consumption

    Create a back end networ solution to process data and responses

    Send meaningful data from switches, accelerometer or magnetometer

View all 4 project logs

  • 1
    Step 1

    The build we adopted is pretty simple. I promised to return the Micro:Bit board unharmed if possible, so adopted bolts and nuts to make the connections rather than solder. Edge connectors and breakout boards are now coming available too for your own projects

    The design required 5 connections to the Micro:Bit, so the 5 bolt holes on the board satisfied both the minimum requirement and an obsessive need for symmetry and completeness.

    Female Dupont headers had one end cut off and were soldered to M3 solder tags to connect to the RN2483 breakout board.

    The RN2483 radio module was soldered to the breakout board. A 10uf capacitor and 8 way header were also added. The optional voltage regulator on the breakout board is not required.

    The connections are then:

    Micro:Bit PinRN2483 Breakout Pin
    GNDGnd
    3V3V3
    0RST
    1Rx
    2Tx

    The following python code needs to be added to the python editor and downloaded:

    # RN2483 LoRaWAN
    from microbit import *
    
    def RN2483_Reset(): # Reset RN2483
        uart.init(57600,tx=pin1,rx=pin2 )
        pin0.write_digital(1)
        pin0.write_digital(0)
        pin0.write_digital(1)
        RN2483_CheckResponse()
        
    def RN2483_SendCommand(command):
        uart.write(command)
        RN2483_CheckResponse()
        
    def RN2483_CheckResponse():
        
        for i in range(100):
            sleep(100)
            if uart.any():
                break
        response_string = uart.readline()    
        
    def RN2483_SendData(data):
        uart.write("mac tx uncnf 1 ")
        for char in data:
            nibble = char >> 4
            if nibble > 9:
                nibble = nibble + 0x37
            else:
                nibble = nibble + 0x30
            uart.write(chr(nibble))
            nibble = char & 0x0f
            if nibble > 9:
                nibble = nibble + 0x37
            else:
                nibble = nibble + 0x30
            uart.write(chr(nibble))
        uart.write("\r\n")
        RN2483_CheckResponse()
        RN2483_CheckResponse()
    
    display.show(Image.NO)
    
    RN2483_Reset()
    #RN2483_SendCommand("sys factoryRESET\r\n")
    RN2483_SendCommand("mac set devaddr 02011E16\r\n")
    RN2483_SendCommand("mac set appskey 2B7E151628AED2A6ABF7158809CF4F3C\r\n")
    RN2483_SendCommand("mac set nwkskey 2B7E151628AED2A6ABF7158809CF4F3C\r\n")
    RN2483_SendCommand("mac set adr off\r\n")
    RN2483_SendCommand("mac set rx2 3 869525000\r\n")
    RN2483_SendCommand("mac join abp\r\n")
    
    display.show(Image.YES)
    
    while True:
        RN2483_SendData(b"BBC Micro:Bit Data")
        sleep(60000)
        
    

  • 2
    Step 2

    The Microbit will initially display an "X", then a tick.

    The setup should then be working and can be seen via the TTN API for the given device address

    The device address in the following line is specific to this device. Other implementer must get a unique device address from the TTN network and change the line to reflect it.

    RN2483_SendCommand("mac set devaddr 02011E16\r\n"
  • 3
    Step 3

    Need to add the TTN and back-end steps here

View all 3 instructions

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