Czy wolisz polską wersję strony elektroda?
Nie, dziękuję Przekieruj mnie tam
p.kaczmarek2 wrote:Hello @lionboy, is your Zmai-90 the same as the one in this topic? Is it using RN8209C? I am asking because there are at least three separate versions of ZMAI-90 around...
startDriver RN8209
p.kaczmarek2 wrote:How do you get bad CRC all the time? Are you really sure your Zmai is on the same chip?
I don't know if that is the problem. I have another one, but that Zmai is now powered on one 3 phase from my house.
p.kaczmarek2 wrote:I don't know, it depends on where that capacitor was connected. Was it just between VDD and GND or somewhere else? I have tested my code only on one Zmai so far - on my own - and it worked well for voltage and power. Furthermore, there were no bad CRCs, and in your case, every packet yields a bad CRC
lionboy wrote:Another 3 of zmai, can you explain how you successfully flash without desoldering the chip?
Thanks
p.kaczmarek2 wrote:Screen is very close to the CBU, you must be careful, maybe cover it with kapton tape?
p.kaczmarek2 wrote:I would like to support screen in OBK, but the screen controller on my device has no marking. Does your screen control IC has a marking?
Maybe it's something from TM1650 family?
p.kaczmarek2 wrote:Well, there is not much choice, when you look at the board, there is CBU, there is that RN chip for power metering, and the only other big chip is for the screen. It's just that it's not marked in my piece, so it's hard for me to tell which chip it is.
TL;DR: If you own the ZMAi-90 CBU version with BK7231N, back up the 2MB flash first, then remove the RN8209C or it will block UART writes. As one expert put it, “TX1/RX1 is for both flashing and TuyaMCU.” This FAQ is for users who want local OpenBeken control, relay switching, and RN8209 power metering without Tuya cloud. [#20827152]
Why it matters: This thread shows the exact failure points, safe flashing path, GPIO map, and early RN8209 support for the BK7231N-based ZMAi-90.
| Method | Read backup | Write OpenBeken | Main limitation |
|---|---|---|---|
| bkWriter 1.60 | Unreliable on BK7231N | Unreliable | Better on BK7231T than BK7231N |
| BK7231GUIFlashTool / newer flasher | Yes | Yes | Still blocked if RN8209C holds UART |
| VDD “trick” with RN8209C still present | Yes, with hack | No | Read worked, write current was insufficient |
| Desolder RN8209C first | Yes | Yes | Requires SMD rework |
Key insight: The blocker is not the CBU module itself. The RN8209C shares UART lines with the BK7231N, so reliable flashing required desoldering the RN8209C before writing OpenBeken.
startDriver RN8209. After starting it, wait about 3 seconds, because early driver updates were slow, then calibrate using a 60W bulb as the reference load, similar to Tasmota practice. The developer reported that voltage and power responded after this process, even before current behavior was fully solved. [#20857064]