[Solved] [BK7231N] How to add BL0939 SPI support for Tuya 2x CT Smart Power Meter Clamp?

Hello, I am looking to get OpenBeken working on a Smart Power Meter Clamp (Dual Channel CT). It is a Tuya-based device with the FCC ID: 2BL6A-WMDL. Inside, the Wi-Fi module is a CB3S (BK7231N). Power monitoring is handled by the BL0939 chip, but instead of the usual UART connection, it is wired via the SPI interface.
I have reverse-engineered the board tracks and identified the complete pinout configuration:
SPI Pins connected to BL0939:
SDO (MISO): P6
SDI (MOSI): P24
SCLK (Clock): P26
Other Function Pins:
CF (Power Pulse): P14
ZX (Zero Crossing): P23
Relay/Control (RL): P8
Button/LED (1K): P7
Since this device uses two current clamps (CT1 and CT2) via the BL0939 SPI interface, I would greatly appreciate it if support for this specific configuration could be added to the driver list (similar to the existing BL0942SPI driver). I have high-resolution photos of the PCB and I am ready to flash any test binary builds to help debug and calibrate the measurements.

For reference, here is the official Tuya DP structure extracted from the device:

* **General:**
* Device ID:

bf00d07292695276fczfts

* **Channel 1 (CT1):**
* Voltage:

cur_voltage

(DP 20)
* Current:

cur_current

(DP 18)
* Power:

cur_power

(DP 19)
* State:

cur_state1

(DP 105)
* Forward Energy (Total):

add_ele

(DP 17)
* Reverse Energy:

ct1_reverse

(DP 115)
* Daily Forward:

ct1_day_forward

(DP 106)
* Daily Reverse:

ct1_day_reverse

(DP 116)
* Record Power:

record_power1

(DP 123)
* **Channel 2 (CT2):**
* Voltage 2:

cur_voltage2

(DP 114)
* Current 2:

cur_current2

(DP 112)
* Power 2:

cur_power2

(DP 113)
* State:

cur_state2

(DP 108)
* Forward Energy:

ct2_forward

(DP 111)
* Reverse Energy:

ct2_reverse

(DP 117)
* Daily Forward:

ct2_day_forward

(DP 109)
* Daily Reverse:

ct2_day_reverse

(DP 118)
* Record Power:

record_power2

(DP 124)
* **Total:**
* Total Forward:

total_forward

(DP 119)
* Total Reverse:

total_reverse

(DP 121)









Thank you for your incredible work on this project!

unlucky for you, I'm currently obsessed with getting AI to try making things.

Here's a BL0939 variant for BK7231N with a new driver that may or may not work. I do not have BL0939 hardware to test
https://github.com/divadiow/OpenBK7231T_App/tree/refs/heads/bl0939spi

startdriver bl0939spi

According to one datasheet, it uses I2C
https://www.alldatasheet.com/datasheet-pdf/view/1490493/BELLING/BL0939.html
To another - SPI or UART
https://evelta.com/content/datasheets/359-BL0939-SOP16L.pdf
In ESPHome, it uses UART
https://esphome.io/components/sensor/bl0939/

The problem is that P6/P24 are neither UART nor hardware SPI.

lol. oh. oh well

First datasheet seems to be for something other with the same name.

Anyway, i would recommend to replace the module with an ESP, disconnect SEL pin and to use ESPHome.

got AI to go deep with Ghidra and the decrypted app partition. It seems pretty confident it's bit-banging SPI for:

SDO (MISO): P6
SDI (MOSI): P24
SCLK (Clock): P26

Added after 13 [minutes]:

an attempt

If it's SPI, then it should be very simple to implement. SPI is using dedicated clock line, it doesn't need precise timings like WS2812. There is nothing wrong with software SPI in OBK.

We could try to support it, but first, just to be 100% sure, how is this pin connected for you?>

Pin 16 SEL, is it on ground, or pulled high? Or floating?

It's a SOP16 BL0939, with SEL on the 3.3V side.

Just to confirm I understand the BL0939 behavior in OpenBeken correctly: where Tuya uses separate states like work_p for import and work_n for export, OpenBeken simply represents this as positive and negative values, correct?


Added after 1 [hours] 6 [minutes]:

>>21924136
Thanks for the amazing effort! The bit-banged SPI pinout (P6, P24, P26) looks like a solid lead. I'll download the zip and test the firmware soon. Will keep you posted!

it's probably not the shape of bl0939 support @p.kaczmarek2 would have in mind, but it would be interesting nonetheless to know if it shows any readings

On this specific board, the SEL pin is directly connected to VDD (measuring 0 ohms between them).

confirming SPI. ok

Great news. Flashed it today and it works! Thank you so much for the custom firmware build, it got the BL0939SPI up and running on my BK7231N device perfectly.
Since this is a stripped-down build, standard console commands like "VoltageSet" or "help" are missing. Could you please let me know how I should pass the calibration coefficients (Voltage, Current, Power) for this specific driver? Should they be added as arguments after "startdriver bl0939spi" in the startup command, or is there another way to calibrate it?


Thanks again for your awesome work!

>>21925040
Commands are named different (or just aliases were forgotten)
https://github.com/divadiow/OpenBK7231T_App/b...824db2a49bf0d61a/src/driver/drv_bl0939.c#L520

@divadiow I want this cleared up and merged

@insmod SetVoltage indeed seems renamed, but what about SetCurrent? It has SetCurrentA and SetCurrentB, we probably need to have some standard.... add second argument to CurrentSet? Channel A and then Channel B? Just wondering

I think it should be in hlw variant, not in a separate one.
And perhaps even merge hlw into power metering variant?
The issue with flash vars is no longer present.

How much of the code is common there? Could it be made DRY?

I can fiddle in a few hours when home. That top table of values is visible when driver is not running too so that needs removing.

Or feel free to take it and sort it out...

>>21925086
THANKS! Helped a lot.

From memory I think it also forces MQTT/HA state or something when driver starts. I imagine this behaviour is not desired.

@geoagache if you're up for more testing please flash the attached. you'll need to assign the IOs the new roles in the config page. driver autostarts on reboot





supported commands


that fixed channel list at the top of the older build will persist unless you reset obk to factory

Sure, will try ASAP.

Flashed today. It's working normally.

ah that's good. Do you have Home Assistant? Has it appeared in there if you've configured it? readings OK? Have you used any commands? do the clear buttons work etc etc?

my empty discovery

Yes, of course, I have HA. MQTT works well. Readings are ok, not sure about power factor and apparent power, though.
Have used commands for voltage calibration, current and power calibration for channel A and B.
Clear buttons work! Pressed them straight from HA .
I use PowerSave 1 as a startup command.
In diagnostic from mqtt HA I can't see device temperature, but not sure I need it.

cool. thanks!

Added after 8 [hours] 31 [minutes]:

maybe ready for PR? This puts the driver in the PowerMetering BK7231N variant.

can always tweak/fix if anything surfaces requiring a change.

https://github.com/openshwprojects/OpenBK7231T_App/pull/2142

insmod wrote:

The issue with flash vars is no longer present.

Hold up! 😁 I was away and trying to catch up - can you elaborate on this a bit more?

>>21927061
As far as i remember, it was a problem because flash vars on beken were limited, and to save HLW data, emetering was hijacked. Or something like that.
Since flash vars were migrated to EF, HLW data is saved under a separate key.

I believe we had 10 or 12 "slots" limit on BK, and at least 3 were in use by default + "quick connect" etc... so rather limiting space to play with ( I may be wrong on the number of "slots" but it is or was a small number). Did we expand the number or is migration to EF introduced something to look into?

That went well, @divadiow , good job.

My only little concern is here - but i think we could ignore it for now:

Can it be more DRY? When we introduce third power meter, we will add third separate function? Is the implementation of data save really that individual?

>>21927077
Slots?
I'm referring to 64 bytes struct
https://github.com/openshwprojects/OpenBK7231...3acdc35f6703050f7/src/hal/hal_flashVars.h#L38
On beken, it's size was hardcoded, so nothing could've been added.
Now, EF area is 32kb, so there's a lot things that it could be used for.
Quick connect data previously was in cfg, now it's in EF