Home > Espressif, Hardware, Linux, Testing > Upgrading Sonoff Stock Firmware to Sonoff-Tasmota – USB to Serial, and OTA Update Methods

Upgrading Sonoff Stock Firmware to Sonoff-Tasmota – USB to Serial, and OTA Update Methods

This post was initially supposed to be part 2 of Sonoff B1 light bulb review, where I would have explained how easy it was to use OTA mechanism to update to Sonoff-Tasmota open source firmware, and shortly show about its features and capabilities. However, it took me over 10 hours to make that work, mostly due to misunderstand in the documentation, and time spent to configure routers. I also failed the first time with Sonoff B1, so I used the serial console method, and instead managed to use SonOTA method with Sonoff POW switching from stock firmware to Sonoff-Tasmota without having to solder or tear down anything.

Updating software with a USB to Serial Board

Using a USB to serial board is the most common method to switch from stock firmware to open source firmware such as ESPurna or Sonoff-Tasmota in Sonoff devices or other ESP8266 based devices. It’s quite straightforward with Sonoff switches like Sonoff TH16.

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You just need to solder a 4-pin 2.54mm pitch header, connect the board, and use esptool to flash the image. One it’s done you can simply remove the wire, leave the header in place, and put the case back in place. But with Sonoff B1 light bulb, it’s quite as easy. First there are no through holes in the board, and you need to solder up to 6 wires on small solder pads.

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The GND, Tx, Rx, and 3.3V must be soldered and connected to the USB to serial board, while GPIO0 must be shorted to enter programming mode, so I also added two more wires for GPIO0, and an extra GND pin.

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Important warning: Never connect the serial board and AC/mains at the same time. Your equipment and life may be at risk.

Now we can download the latest version of the firmware, install esptool, connect the USB to serial board to your computer – which will also provide powered to the board -, and run esptool to flash the firmware:


That’s pretty straightforward, and the output should look as below if everything runs normally:


Most products on the market defaults to access point mode when they are first booted, but Sonoff-Tasmota’s developer have instead decided to provide pre-built image in client mode connecting to a default access point with SSID: indebuurt1 ; password: VnsqrtnrsddbrN. That’s a bit of a pain, as you need to configure another router with those credentials, before changing it to your home router. An alternative way is to build some source, and change the default AP settings, so the device can connect right away after flashing. Still, I’d wish an image that default to AP mode would be nice. It’s actually not a problem for most Sonoff devices, as you can switch to AP mode with the button (4 short presses), but Sonoff B1 does not have one.

Now imagine you have a dozen or more of Sonoff B1 light bulbs that need to be update to Sonoff-Tasmota. That would be a real pain to solder and unsolder the required wires for each bulbs. One solution is to create a jig with pogo pins for firmware update, as the one shown below specifically designed for AI Light. You just need to pop out the bulb, click the jig, flash over serial, remove the jib, refit the bulb, and you’re done.

I don’t know if one exists for Sonoff B1, but the jig above could certainly be customized to work with it.

SonOTA – Sonoff OTA Firmware Update Method

However, in an ideal world you’d prefer not to mess with the hardware at all. If only ITEAD Studio provided a way to upload custom firmware with their stock firmware that’d be ideal, but it’s not the case right now. Luckily, the OTA mechanism was reverse-engineered, and SonOTA is an (experimental) implementation that allow to flash alternative firmware to Sonoff devices without altering the hardware or needing special jigs.

The method on Sonoff-Tasmota wiki does not work on Sonoff B1 because there SSID is not advertised in pairing mode, but somebody in github had managed to update one light bulb using DNS spoofing. Since I used the first method with Sonoff B1, but only partially managed to make it work, I switched to Sonoff POW, and succesfully tested the DNS spoofing method.  Several items are required, so I’ve drawn a diagram showing how those interact.

  1. The Home Router is just the WiFi router you’d normally use to access the Internet
  2. The smartphone with eWelink is requirement to configure WiFI on the Sonoff device, and update it to the latest stock firmware version. It can also be used to easily check access points.
  3. The WiFi laptop runs SonOTA, and will act as ITEAD Studio firmware update server located at xx-disp.coolkit.cc (for example cn-disp.coolkit.cc, eu-disp.coolkit.cc, etc…)
  4. “Temporary” Router with DNS spoofing will make sure xx-disp.coolkit.cc redirect to your laptop/computer running SonOTA, so it takes over when Sonoff device tries to update the firmware. It still needs to be connected to the Internet.
  5. Sonoff device – The device we want to update

Potentially, you could combine the router, router with DNS spoofing, and WiFi laptop into one device, if you have a Debian based router, but I still separate all three in my case, since home router does not support DNS spoofing, and I failed to install SonOTA on the temporary router.

The very first step is to pair the Sonoff device with eWelink app, connect it to your home router, and update the firmware to the latest version, in my case 2.0.4.

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Now you can configure your temporary router to use DNS spoofing. I did not have any spare router with such feature, so I instead used VS-RK3399 board with Debian, and configured it as a router with hostapd, and isc-dhcp-server using those instructions. This part will heavily depend on your router, and whether you use Debian, or other Linux distributions. For reference, here are some of the main configuration files I used:

  • /etc/hostapd/hostapd.conf

  • /etc/network/interfaces

  • /etc/dhcp/dhcpd.conf


The next step was to configure DNS spoofing. I first went with dnsmasq, and I could successfully confirm it worked with dig, but for whatever reason Sonoff B1/POW would still connect the ITEAD server. Finally I tried with dnsspoof, and it worked OK.  Installation in Debian:


/etc/dnsspoof.conf configuration file to redirect traffic to ITEAD / eWelink update servers to my WiFi laptop:


You can run it as follows:


DNS spoofing took me the most time, as beside restarting service in the router itself, you have to restart the devices connected to it to reflects the changes. I also messed with /etc/hosts file in the router and laptop, but it should not be necessary, as the important is to fool the Sonoff device.

Let’s switch the WiFi laptop configuration. It should work with both Linux and Windows, but mine is running Ubuntu 16.04, so that’s what I used. Let’s create a working directory, get SonOTA code, and install all required libraries and tools.


Now we’re ready for the update. Launch SonOTA script in legacy and no provision modes:


This will first ask you to select the WiFi interface, and enter your SSID and password, and start probing for the Sonoff device:


Delete your Sonoff device in eWelink app, and restart pairing, this time connecting it to your temporary router with DNS spoofing enabled, and shortly after the SonOTA script should start to transfer the image to the device:


Now you should be able to use your smartphone or the laptop to connect to FinalStage access point, start a browser to access http://192.168.4.2. You should see the interface below, click on scan for Wifi network, and select the one you want to replace indebuurt1 SSID, in order to connect to your “home router”.

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Click on the button Save on the bottom of that page, and after a while you should be able to access Sonoff web interface into your home network

Output log of SonOTA.py script for that last step:

Success! Finally… Now you can configure Sonoff-Tasmota to use your actual device – in my case Sonoff POW – instead of Sonoff Basic. I’ll show a bit more about that while testing Sonoff B1 with Sonoff-Tasmota in an upcoming post. Whether you choose between the serial or OTA method will depend on the number of devices you have to update, and/or whether you prefer soldering or messing around with network settings. If you are after maximum efficiency for a large number of Sonoff B1 light bulbs, then a jig with pogo pins should be by far the fastest way to reflash them all.

  1. Gaetano
    October 4th, 2017 at 21:44 | #1

    Great news! Please tell us when this will also work with your Sonoff POW! 🙂 Tks!

  2. tmunzer
    October 4th, 2017 at 22:03 | #2

    May be i’m utterly stupid, but using something like an orangepi PC+armbian+pi-hole(as dns server) + Sonota ; linked by ethernet with Router could have been and easier setup ? Did I miss something ?

  3. willmore
    October 5th, 2017 at 06:35 | #3

    You just need to pop out the bulb, click the jig, flash over serial, remove the jib, refit the bulb, and you’re done.

    Yar! Ye be late for International Talk Like a Pirate Day, there, matey!

  4. Karl Johnson
    October 6th, 2017 at 03:16 | #4

    I found upgrading firmware once tasmoto is installed is 2 step when i tried. Had to do a minimal upgrade then upgrade to final.

  5. October 6th, 2017 at 09:11 | #5

    @Gaetano
    I used it with the Sonoff POW in the article, as it failed with Sonoff B1 with my first attempt. But the method i used will also work for Sonoff B1.

  6. October 6th, 2017 at 09:16 | #6

    @tmunzer
    It’s a long article, so maybe you missed the part where I explain you could combine the router, temporary router and laptop into one.

    IMHO, the easiest & cheapest way if you’re going to use the OTA method and already have a laptop, is to get an openWrt router and enable DNS spoofing.

  7. October 6th, 2017 at 09:17 | #7

    @Karl Johnson
    Those are the instructions for Stock to Sonoff-Tasmota. Once it’s already installed it’s much easier.

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