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How to flash LN882H with open source Tasmota/Esphome style firmware - backup procedure included

p.kaczmarek2 63507 297

TL;DR

  • LN882H modules can be flashed over UART with open-source Tasmota/Esphome-style firmware to free cloud-controlled devices and integrate them with Home Assistant.
  • Wire module TX, RX, GND, 3V3, and BOOT/GPIOA9 to ground, and keep GPIOA9 low throughout the entire flashing process.
  • Backup uses `python LN882H_Flash_Dumper.py COMx flashdump`, and the firmware flash command is `LN882H_CMD_Tool.exe COMx download flash 921000 0x0 flashimage.bin`.
  • After flashing, power-cycle the module, disconnect BOOT from ground, and open 192.168.4.1 to configure it like other OpenBeken/Tasmota-style devices.
  • A reliable external 3.3V supply is recommended because powering directly from the USB-to-UART adapter’s 3.3V pin may fail.
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  • #211 21072601
    divadiow
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    Very cool. I've been spying on your PR to see how it's going!
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  • #212 21072603
    p.kaczmarek2
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    My PR is very chaotic because I don't even have compiler setup locally and I am doing other things in the background but I finally managed to get stuff displayed.
    LED display showing digits 8.8.8.8 on a circuit board.
    To simplify things, I have a "shared TMGN driver" which supports multiple similiar display controllers like TM1637, TM1638, GN6932, etc.

    Added after 27 [minutes]:

    Ok it's working I guess:
    Screenshot of a command line tool for managing display drivers.
    Close-up of a circuit board with an LED display showing numbers 1.8.9.4.
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  • #213 21072807
    max4elektroda
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    p.kaczmarek2 wrote:
    >>21072408
    Guys, do you have B9 gpio working on your LN882Hs? For me, it's in high state all the time and OBK can't control it.

    That's probably, because B9 is Tx1 (so you will find your serial logs there on a physical port - at least this is where I get my logs from ;-))

    TX1 I/O UART_TX1 pin for log printing, corresponding to the GPIOB9 pin (pin 30) of the IC.
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  • #214 21072817
    divadiow
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    indeed, but why isn't it controllable? are RX/TX GPIOs always fixed high? The datasheet says FULLMUX, like other controllable GPIOs...
  • #215 21072820
    p.kaczmarek2
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    max4elektroda wrote:
    [
    That's probably, because B9 is Tx1 (so you will find your serial logs there on a physical port - at least this is where I get my logs from ;-))

    Wait, but my module has TX and RX on the other side... so there are two UART ports, like on Beken? Well, that makes sense...
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  • #216 21072827
    max4elektroda
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    Yes, there are two UARTS. On my WL2S module, the ports are on the back and labeled accordingly:

    https://obrazki.elektroda.pl/7439873600_1708165255.jpg

    So I think they are defined as UART somwhere, making any other setting useless.
    At least, I didn't even see glitches in serial log, if I change B09 in UI ...
  • #217 21072943
    p.kaczmarek2
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    Well, my module is different, you can see that I have B9 on the back and I was suprised that this B9 was not working:
    Electronic circuit board with connected logic analyzer and additional components. Image of an electronic module with B9 marking, with wires soldered to terminals. Close-up of an electronic module with visible pin labels: 3V3, GND, RX, TX, A1, A0.
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  • #218 21073113
    max4elektroda
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    That's why I pointed out, that I had the advantage of my module having the UART ports labeled not as gpio pin but as Rx/Tx.
    So I would call it: "works as designed" ;-)

    And I can only tell, that I like this feature: If you connect a 3.3V com port, you will be able to see the log with the unusual settings "921600 8N1".
    That's very useful e.g. to see if there are WiFi problems, which you obviously can't see in the JS apps Log section...
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  • #220 21073179
    max4elektroda
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    Piorun2002 wrote:
    >>21070551
    I turned off some test MQTT options (hass / tele discovery) and it seems to work well
    [...]
    after enabling the options:
    Code: text Expand Select all Copy to clipboard
    Flag 27 - [HASS] Invoke HomeAssistant discovery on change to ip address, configuration
Flag 30 - [MQTT] Enable Tasmota TELE etc publishes (for ioBroker etc)


    the problem started occurring again

    @Piorun2002 : Could you please try if this issue also occurs, if you use this functions with a release image (without LFS)?
  • #221 21073185
    p.kaczmarek2
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    As far as I know the MQTT instability is a well-known issue that spreads accross many SDKs and it's related to the multithreading in LWIP.

    @valeklubomir fixed it on BK7231N platform some time ago by updating LWIP:
    https://github.com/openshwprojects/OpenBK7231N/pulls?q=is%3Apr+is%3Aclosed
    https://github.com/openshwprojects/OpenBK7231N/pull/3
    Some things like LWIP_ASSERT_CORE_LOCKED were added and it increased the stability.

    There is also a smaller stability fix possible for LWIP MQTT:
    https://github.com/openshwprojects/OpenBL602/commit/c73dcaab7e73ab68b29bd20a3b5d4c0992902c1d
    ... but from I can see, it's already applied to LN882H:
    https://github.com/openshwprojects/OpenLN882H/commit/15fde0f403e408eab6ffa31d0e5711e97c37afe2

    Of course, I am not saying that I am certain that this is the cause of the instability, but I know it was for BK7231N..
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  • #222 21083012
    vovatvset
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    Hi! How do I reset password web ui? the original firmware does not reset the password web ui(
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  • #223 21083723
    max4elektroda
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    The OpenLN882H firmware usually has no password...
    So, did you configure Web authentication here or do you mean how to reset a password in the original firmware?
  • #224 21083773
    p.kaczmarek2
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    I think he has set password for OBK web ui and now tries to remove it. Well, that could be problematic! Flashing original firmware may not overwrite the config partition. He may need a custom OBK build that will let him to remove the password or change it to something else...
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  • #225 21083917
    max4elektroda
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    Shouldn't it just be "remove the check in OBK GUI" and the password is no longer used?? Web authentication configuration interface with an empty password field.

    Added after 19 [minutes]:

    Or is the question: how to remove an unknown password?
  • #226 21083958
    p.kaczmarek2
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    I think he forgot his password and now he is trying to hack into his own device. That can be problematic.
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  • #227 21084157
    max4elektroda
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    I see. We might be able to provide a quick solution in changing this code to always ignore auth in safe mode

    https://github.com/openshwprojects/OpenBK7231...lob/main/src/httpserver/http_basic_auth.c#L12

    But this has the drawback, that the config is revealed.
    A better idea would be, only to allow a "full reset" of all settings and password in one.

    So what about something like it's done on Fritzbox: during the first x minutes, you can initiate a reset if password is wrong?

    Of course, it could also be something like a special clear config image, which will erase "all" settings and then starts in safe mode to allow OTA for a regular image. This would mean that there is no change in "regular" releases
  • #229 21084206
    p.kaczmarek2
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    This file is responsible for auth:
    https://github.com/openshwprojects/OpenBK7231T_App/blob/main/src/httpserver/http_basic_auth.c
    There is a define for that:
    Screenshot of the source code in the http_basic_auth.c file on GitHub.
    If you compile without ALLOW_WEB_PASSWORD defined, any connection will be accepted.
    You can also just manually edit code to accept any password. Then flash via UART.

    Here is a guide showing how you can compile OBK online, without any setup on your PC:
    https://www.elektroda.pl/rtvforum/topic4033833.html#20946719
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  • #230 21084699
    max4elektroda
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    I tried to implement a "general" possibility to reset the configuration, if "http auth" fails more than x times during the first minutes after startup.
    If you have a git account, you can download the "artifacts" there, containing an image for LN882H, too.
    https://github.com/openshwprojects/OpenBK7231T_App/pull/1240

    If you reset the device and give a wrong password more than 5 times, you will be asked if you like to reset the configuration of the device....



    Device configuration reset dialog box in the browser.
  • #231 21085363
    vovatvset
    Level 4  
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    I'm new and I don't know how to build the firmware. Here, no matter who, can I build a firmware without a web password for ln882h

    Added after 1 [hours] 45 [minutes]:

    >>21084699
    Thanks, I'll check this method.
  • #232 21085618
    max4elektroda
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    If you dont have a git account, here the two images (OTA and UART) for LN882H
    Attachments:
    • OpenBK7231T_App_1240_merge_3e934fccc8ca.zip (734.98 KB) You must be logged in to download this attachment.
  • #233 21085644
    Piorun2002
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    max4elektroda wrote:
    If you reset the device and give a wrong password more than 5 times, you will be asked if you like to reset the configuration of the device....

    I think that, for security reasons, there should be a flag to enable/disable this functionality in the configuration
  • #234 21085669
    p.kaczmarek2
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    vovatvset wrote:
    I'm new and I don't know how to build the firmware. Here, no matter who, can I build a firmware without a web password for ln882h

    This is why have guides for beginners here: https://www.elektroda.com/rtvforum/topic4033833.html#20946719

    max4elektroda wrote:

    https://github.com/openshwprojects/OpenBK7231T_App/pull/1240
    |
    While this looks good and sounds useful, it's still a potential security breach. Can you encapsulate your code into something like #ifdef ENABLE_OBK_AUTH_RECOVERY ? Then I will happily merge your changes.
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  • #235 21085703
    max4elektroda
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    This is discussable, one could argue, you usually don't know in advance, whether you will loose your password ;-) - just kidding.

    I tried to make a proposal with a decent measure of a calculated risk:
    You will need (kind of) physical access to the device to restart it: the mechanism will only work the first x seconds after a restart (in PR: 180 seconds) .
    If this is implemented, the time should be a compromise:
    - need for this procedure (lost password) will usually mean you have to repower it
    - it might take some time from the device to your browser to configure it.

    You can't reset the web password (and so expose the settings) but only do a full reset of all settings.

    My idea behind this proposal: a person who has physical access to restart the device can usually do whatever he/she wants with the device.
    So resetting it was not so much of an additional risk (I thought) ...

    Added after 2 [minutes]:

    p.kaczmarek2 wrote:
    Can you encapsulate your code into something like #ifdef ENABLE_OBK_AUTH_RECOVERY ? Then I will happily merge your changes.

    Sure, no problem.

    Added after 4 [minutes]:

    As an additional point: I first thought of "you need to press the button during the procedure".
    But since we don't handle some fixed devices with known properties (a single module might even have none) I thought of this alternative.
  • #237 21085784
    Piorun2002
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    max4elektroda wrote:
    As an additional point: I first thought of "you need to press the button during the procedure".

    now is an option: "Enable web authentication"
    so you can add the "Disable password reset" extension
    when setting a password, you decide whether you want to disable this option
    that would be very intuitive
  • #238 21085902
    max4elektroda
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    Piorun2002 wrote:
    so you can add the "Disable password reset" extension
    when setting a password, you decide whether you want to disable this option
    that would be very intuitive

    Yes, indeed, very good point to decide here!
    I'll try make this possible, another flag would probably the best for this.
  • #239 21085906
    p.kaczmarek2
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    I can agree for a flag, but would that flag be on or off by default?
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  • #240 21085933
    max4elektroda
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    I would vote for the reset be possible in default (so on/off depends on if it's "enable possible config reset" or "disable possible config reset").

    But there are arguments for both:

    If there haven't been too many questions about lost passwords, it doesn't seem a big issue
    It's a possible security breach

    As stated above: everyone with physical access can do more harm than resetting the configuration
    It's only possible for a very short period of time
    We are talking about web auth with plain HTTP, so everyone in the network can read the credentials (they are only encoded but not encrypted)

    It should work as a simple way to overcome a possible lost password, so in my opinion, if disabled by default it won't be a help).
    At least at the moment I think most users are willing to flash a precompiled image but not to compile one themselves. If that was the case I would vote for completely disable it and every user with a forgotten password could easily compile a recovery image.

    I will accept all decisions and code it as you like ;-)

    All in all it was not too much of work, so even if it doesn't at all make it's way to the image, it's not a big deal.
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Topic summary

✨ The discussion focuses on flashing LN882H modules with open-source firmware similar to Tasmota/Esphome, enabling cloud-free operation and integration with Home Assistant. Flashing requires a USB to UART converter with reliable 3.3V power supply, connecting module TX to UART RX, RX to TX, GND to GND, and 3.3V to 3.3V. Users report challenges including access to the BOOT pin, interference from board components on RX/TX lines, and the necessity of short wiring to ensure stable flashing. Various USB to UART converters (CH340, FT232RL, PL2303, CP2101) have differing success rates; CH340 and CP2101 are recommended over some FTDI and PL2303 adapters. Correct baud rate (115200) and running the flashing tool from non-system drives (e.g., D:) improve success. The LN882H_CMD_Tool is used for flashing and dumping firmware; flashing requires power cycling and keeping BOOT grounded during operations. Users successfully dumped firmware but often encountered "Fail. Error downloading file" during flashing, resolved by adjusting baud rate, shortening cables, and using compatible USB-UART adapters.

Power-saving features are under active development; enabling PowerSave mode reduces power consumption and device temperature but may cause WiFi connection issues in some firmware versions. PowerSave commands can be set via startup commands or command tool, with better effect when applied directly via command tool. Temperature monitoring shows LN882H devices run hot (up to 74°C) without load, improved by PowerSave mode. Integration with energy metering (BL0937) is affected by PowerSave due to interrupt handling. Static IP assignment is currently unimplemented in firmware. DHT sensor support is partially implemented; drivers require manual start commands, and pin mapping must be correct. NTP client requires manual driver start and supports server IP configuration via commands. Safe mode can be triggered by power cycling to reset device settings. Firmware and tools are evolving with ongoing commits addressing power management, filesystem (LittleFS), and device stability.

Overall, flashing LN882H modules demands careful hardware setup, compatible USB-UART adapters, correct flashing parameters, and power cycling. Firmware features like power saving, sensor support, and network configuration are improving but still have limitations. Community contributions and testing continue to enhance LN882H open-source firmware usability and integration.
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FAQ

TL;DR: 70 °C internal temperature was logged on stock settings, but drops to 32 °C after PowerSave 2; “LN882H flashing is very similar to ESP8266 flashing” [Elektroda, p.kaczmarek2, post #20923772] Use 115 200 baud and keep BOOT (A9) low for reliable uploads [Elektroda, voodoopt, post #20958664]

Why it matters: Correct wiring, speed and power rules prevent bricked modules and overheating.

Quick Facts

• Flash size: 2 MB NOR, dump script trimmed to 0x200000 bytes [Elektroda, divadiow, post #21284784] • Stable upload speed: 115 200 baud; 2 Mbit/s often fails [Elektroda, voodoopt, post #20958664] • BOOT=A9 must stay at GND from power-on until flashing ends [Elektroda, p.kaczmarek2, post #20905518] • PowerSave 2 cuts idle current from ≈55 mA to 35 mA (-36 %) [Elektroda, max4elektroda, post #21064064] • OTA bug fixed in releases ≥1.17.789; Firefox now works [Elektroda, divadiow, post #21332121]

1. What minimum hardware is required to flash an LN882H module?

  1. USB-to-UART adapter that outputs true 3 V3 (CH340 or CP2102 proven). 2. Solid 3 V3 supply ≥300 mA; many adapters sag. 3. Five leads: 3 V3, GND, RX, TX, BOOT (A9). 4. Optional: pogo pins or fine wires for in-circuit work [Elektroda, p.kaczmarek2, post #20905518]

2. Which pins go where?

• Module TX → UART RX • Module RX → UART TX • 3 V3 ↔ 3 V3 • GND ↔ GND • A9 (BOOT) ↔ GND (keep low) Any disconnect of A9 before power-cycle aborts flashing [Elektroda, p.kaczmarek2, post #20905518]

3. How do I enter download mode every time?

  1. Hold A9 at GND. 2. Remove and re-insert USB power to both UART and module. 3. Start flash command. After any failure repeat the full power cycle—soft reset is not enough [Elektroda, p.kaczmarek2, post #20933029]

4. Flash tool stops with “Fail. Error downloading file”. Fix?

Set baud to 115 200 bps; many CH340/FTDI clones error at 2 000 000 bps. Example: “Ok.” after lowering speed on COM21 [Elektroda, voodoopt, post #20958664]

5. Can I flash without desoldering the module?

Yes, if you can grip A9 and ensure RX/TX lines are not tied to buttons or capacitors. Cut the trace or lift parts if debouncing cap blocks UART [Elektroda, p.kaczmarek2, post #20923772]

6. Quick 3-step firmware backup before experimenting?

  1. python LN882H_Flash_Dumper.py COMx flashdump 2. Wait ~5 min for 2 MB readout. 3. Verify flashdump_flash.bin size == 2097152 bytes [Elektroda, divadiow, post #21284784]

8. How do I enable PowerSave automatically?

Add in Startup Command: backlog delay_s 5; PowerSave 2. From release 1.17.772 the firmware applies PowerSave after Wi-Fi connects, so no boot lock [Elektroda, max4elektroda, post #21064290]

9. Edge-case: BL0937 energy meter shows 125 V after PowerSave.

PowerSave disables the interrupt clock BL0937 needs. Keep PowerSave 0 on power-monitor plugs or voltage reading will be wrong [Elektroda, max4elektroda, post #21052031]

10. OTA upload crashes when I use Firefox. Work-around?

Firmware ≤1.17.772 overflowed a 4 kB buffer when the header and payload arrived in one TCP packet, often triggered by Firefox. Patched in 1.17.789 (PR #1441) [Elektroda, max4elektroda, post #21319958] Use Chrome or update firmware.

11. How can I reset a forgotten Web-UI password?

From 1.17.800 you can power-cycle, then enter 5 wrong logins within 3 min; firmware offers full config reset unless Flag 77 disables it [Elektroda, max4elektroda, post #21086964]

13. Linux/Mac flashing tool available?

Yes. Open-source LN882Loader (CLI) handles dump and flash on Linux/macOS; requires PySerial [ste­fanmandl, 2025].

15. How do I change a duplicate MAC address?

mac write xx:xx:xx:xx:xx:xx works but device reboots with new IP. Verify the MAC is unique before saving [Elektroda, Advian1, post #20996463]

16. Quick How-To: flash in 3 steps

  1. Hold A9 → GND, power module.
  2. LN882H_CMD_Tool COMx download flash 115200 0x0 OpenLN882H_xxx.bin
  3. Power-cycle, release A9, connect to AP 192.168.4.1 and configure.
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