Sensebender/Dualoptiboot OTA HowTo in Mysensors

  • Hardware Contributor


    Here is an howto about OTA in Mysensors I made for jeedom french users when Mysensors 1.5 was released. So I translated it if it can be useful to you. Things should not have changed a lot I think. I have no time for the moment to check everything. So if you note differences, tell me here and I will update. I will update pics with latest revision of the software.

    OTA, or Over The Air, lets you upload your sketch without ftdi, it's done wirelessly. Can be useful if your nodes are not accessible or you need to make signing changes for instance. To get this nice feature, you need to burn a dedicated bootloader.

    In Mysensors, we can use two kind of OTA:

    • 1st option : MYSBootloader, created by Tekka from Mysensors Team.
    • 2nd option : Dualoptiboot or if you prefer Sensebender Bootloader (in Mysensors boards). But in this tutorial I will name it "Dualoptiboot". It comes from Lowpowerlab.

    Difference between these two methods (updated from Tekka post

    • MYSBootloader does not require external flash: OTA FW updates are transmitted offline, i.e. MYSBootloader communicates with the controller and receives new FW which is directly written to MCU, once FW is transmitted and CRC verified, MYSBootloader hands over to the new sketch/FW.
      Pro: recovery OTA possible, also with a faulty/buggy sketch (if sketch freezes, watchdog resets and MYSBootloader takes over), no external flash required
      Cons: Radio specific, i.e. different bootloader for RF24 and RFM69 radio (rfm69 work in progess) necessary, offline (no sensor data processing possible during ota).
    • Dualoptiboot requires external flash: OTA FW updates are transmitted online, i.e. while the node is active. Once all FW packets are transmitted and CRC verified, the node reboots, dualoptiboot copies FW from external flash to MCU and hands over to the new sketch/FW.
      That means too that you need to ftdi upload your node sketch the first time or ota won't work yet as it is handled in the sketch.
      Pro: Radio agnostic (no radio specific code in bootloader so can be used in different scheme/protocols..), online (while node processes sensor data)
      Cons: Faulty FW (e.g. freezing sketch due to bad coding) cannot be recovered OTA => recovery via serial port necessary, external flash required

    This tutorial is only for Dualoptiboot Bootloader, because I have not seen an howto for this option here yet. But some parts/pictures of this howto can be used for MYSBootloader upload.
    If you want to use MYSBootloader, howto is here:

    By default, Dualoptiboot bootloader is 8Mhz Internal + 1.8V BOD.

    What do you need:

    Burn Dualoptiboot in your node

    To keep things simple, or maybe not for others..imho it's so easy with a cheap usbasp (just few wire) than arduino as isp.

    What looks my usbasp (clone, USBASP 2.0 LC Technology) and connections to your arduino or node.

    Wiring on nano/micro/328p:

    MOSI : D11
    VTG : VCC 3.3V
    GND : GND
    SCK : D13
    MISO : D12

    Once it's wired, burn fuses with avrdudess. Here the conf:


    Note : even if my usbasp is a clone, I choose genuine usbasp in the listbox.

    Just click on Write in "Fuses&Lock bits" section. Then read it to check fuses are well burned.

    Now don't disconnect your usbasp.

    • Go to arduino ide, choose SensebenderMicro, Processeur Atmel328 8Mhz, serial COM port, and USBASP programmer.
    • Click Tools\Burn bootloader. You will get few SCK warning but that's not a problem, it's because I have an usbasp clone.
      Note: you could use avrdudess to burn the bootloader too.



    Yeah, our OTA bootloader is burnt 🙂

    In sketch

    To enable OTA in your sketch, you need to add


    or uncomment it in Myconfig.h

    OTA management is completely transparent. Everything is well handled in process() and wait() methods (when you do a gw.wait or mynode.wait for instance...)

    Important note :

    • Don't forget a sleeping node can't receive an OTA. You can wait after wakeup for instance to see if you have somethings coming or I have not tried it yet but it seems now in mysensors libs there is smartsleep() wich manage the wait() after wake up.
    • when you upload the new sketch, it is done during runtime, so you have to handle/optimize this in sketch. The best is if you detect an OTA msg, to pause process or sensors readings during the process or it will affect the speed of the OTA. I mean for instance if you read sensors, sometimes there are some delays in libs, all these things will delay ota or timeout it during main loop. Plus, if these optimization are not done and you run on battery, the longer time in TX/RX radio for the update, the more battery energy wasted. OTA can be fast 15-30sec if nothing slow it, or x minutes if not optimized 😮
      So it's up to you to manage this, use non blocking/asynchronous code. The rest of the process is again completely transparent. Great!

    How to upload a new sketch just with OTA

    For this I use MYSController. It's not an .ino file that you will upload but the .hex one. So to easily get this file:

    • In Arduino ide, go to File\Preferences, on bottom click on preferences.txt. It opens preferences.txt.


    • Keep this file opened and close arduino ide (otherwise your changes will be erased).
    • In preferences.txt, at the end, add this

    or another preferred path. It will be there you will find your .hex compiled sketch files.

    • Open arduino ide and compile/check your node project. You should now see your compiled files in the path you have set.
    • Copy the .hex to Firmware path of MYSController

    Launch your OTA update

    • Launch MYSController and in Config/Serial, check the right serial com port.
    • Click on "Refresh FW repo" so you can use your new .hex file.
      Note : When I tested this it didn't work for me so I needed to do this
      In Firmware folder, edit firmware_config.csv and manually add your .hex. Here an example where I added a Humidity .hex file for tests.
    10,Blink,1,Blink.hex,blinking example
    100,Sensebender Micro,1,SensebenderMicro.cpp.hex,Sensebender Micro
    110,Sensebender Blink,1,SensebenderBlink.cpp.hex,Sensebender Blink
    120,Sensebender HumidityTest,1,HumiditySensor.cpp.hex,HumidityTest
    • Now to wirelessly send your new sketch to your node, simply right click on the node you want to update. For sleeping battery node, choose "Battery powered Sleeping". So when your node will wake up, MYSController will resend the update. Awesome!
    • click on Assign FW,
    • choose the sketch

    and voilà! OTA should start, and then your node will reboot.


    I hope to have not missed something important. Please tell me, and I will add in this post.
    This howto was made some months ago, so I'm note sure if it's exactly still the same, but that should be almost ok. Try and test 😉 and tell me. I hope it will help at least, as it is something often asked..If all is ok, don't hesitate to put it on a better place (I'm not sure if it's the best place here)


  • Great tutorial. It is now more clear for me.
    I'll update you with my results within 2 weeks... i hope 🙂

  • Hardware Contributor

    @tekka I have updated the first part of this howto. Can you just tell me if it looks ok for you, less ambiguous, missing important notes, please ?? Thx in advance 🙂

  • @scalz

    Nice tutorial.
    I already bought and received your eval board. I ordered it more for ATSHA204A but OTA is interesting.
    Is OTA using eeprom possible with RFM69 ? I imagine that it's the case.


  • Hardware Contributor

    @carlierd: hi. thx 🙂 Yes you're right, you can use both nrf or rfm69 radio with this dualoptiboot ota (no radio code in bootloader).

  • Hardware Contributor

    @scalz Great tutorial thanks. I plan to give it a try this week end but I was wondering if you had any test sketch to check if the arduino can talk to the flash.

    Just a quick way to test, before flashing a new bootloader, if all pins are correctly soldered.

    So far I know that ATSHA204A is recognized as I can read the config but no luck finding anything similar for the eeprom.

  • Hardware Contributor

    you can use example sketch from spiflash lib 😉

  • Hardware Contributor

  • Hardware Contributor

    Start...Init FAIL!

    Well I guess something is wrong

  • Hardware Contributor

    depending on the eeprom you're using, you may need to change the corresponding jedec code in the sketch (I don't remember well). you can find the eeprom jedec code in datasheet if not the same. but in mysensors it should work. or you have a bad wiring perhaps..

  • Hardware Contributor

    Got it, thanks @scalz !

    I had indeed to remove the ID from

    SPIFlash flash(FLASH_SS, 0xEF30);

    and leave it blank (or use 0x1F65 for the AT25DF512C):

    SPIFlash flash(FLASH_SS);

    Next step OTA flashing... but tomorrow.

  • Hardware Contributor


  • I have AT25512N-SH-T SOIC-8 ->
    I so have a different bootloader - I think I can use it with the flash as it does have 8 pins socket.

    However, I am a complete noob when it comes to the OTA. Is this the way to do it:

    1. Burn Optiboot onto the Sensebender
    2. Why do you have external eeprom board? I think the Sensebender has 64kb SPI flash / e2prom onboard.

    Thanks for an excellent tutorial.

  • Hardware Contributor

    i don't know for your eeprom, i don't have time right now, but that need to check datasheet, same pin footprint is not enough.

    1. you need to burn DualOptiboot, it's not optiboot. Optiboot does not handle ota.
    2. The board is an eval board for ota/auth. that's all. it could be used in some diy projects but i integrate the eeprom on my pcbs of course.

  • @scalz Thanks! The sensebender had already the eeprom IC right? So no need to do anything external

  • Hardware Contributor

    @alexsh1 yes, no need. thx for feedback. I will modify my howto and add a link to the post relating eeprom compatibility too.

  • @scalz only the bootloader change to Dualoptiboot on a node is required with some change of code, right? Does eeprom IC have to be programed as well or it is fully changed by Dualoptiboot + sketch?

  • Contest Winner

    Thanks for this incredible tutorial. 👍
    I've found almost all answers here and now I want only confirmation of my thoughts 🙂
    I am prepearing my Wall Socket insertable node for production so I am making latest changes on the board. I decided to add SPI flash to implement OTA ability (see picture - U5). I plan to use dualboot.
    alt text
    As I understand the sketch works during loading firmware over the air, so it doesn't matter how much time it takes because my sketch can send heartbeat impulses to external watchdog during updating. Is it correct?
    Second, I didn't want to add spi flash to Wall switch insertable node, but now I am having doubts. If I understand correctly there is no problem to update sleeping node because it will get update messages when it wakes up. Is it true? 🙂

  • Hardware Contributor

    @koresh thx i'm glad if it helped you.

    1. not sure what you mean with "how much time... because external wdt". I was referring about the time it could take for battery powered device. because some sensors lib can have delays for instance, and keeping the readings process during ota could slow ota reception. but I have not checked the behaviour in the new lib yet.
    2. I think so, depending of the controller used.

  • Plugin Developer


    Make sure you wait for a little bit (~300 ms) before going back to sleep in the sketch, to give the controller time to send the reboot command to the node. The firmware config request is sent from the node in the begin method.

    When I implemented firmware updates in the pymysensors library I made sure to only send the reboot command after receiving a set command from a node. That way the node should be awake to receive the reboot command if it waits a bit before going back to sleep. I'm not sure how the other controllers that support ota firmware updates have solved this.

  • Any sample optimised sketch for the OTA enabled sketch?

  • @scalz A useful addition could be that the controller only runs on Windows. I bumped into this limitation after quite a few succesful steps. Is there a Linux or Java alternative?

  • Hardware Contributor

    will think about it 🙂 afaik there isn't any simpler linux or java alternative yet. I'm windows user and MYSController is very handy.
    that said you can take a look here for controllers supporting FOTA , maybe ..

  • @scalz Mycontroller works fine, I just tested it with Dualoptiboot and last package version (ask in the forum).

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