[BK7231T - WB2S] mERKURY WiFi power plug

akosschneemaier 08 Dec 2022 03:02 1 2178 Cool? (+3)

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TL;DR

Merkury MI-WW218-199WW WiFi power plug teardown identifies a WB2S module based on the BK7231T.
Flashing used OpenBK7231T_App after opening the plug and connecting a Raspberry Pi with a serial adapter.
The plug needs 3.3 Volt for flashing, but the Raspberry Pi 3.3V output is not sufficient.
App settings were straightforward: P6 Btn 1, P8 LED_n 1, and P24 Rel 1.
Opening the device is hard, and a strong utility knife can damage the PCB enough to require extra soldering.

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Hello Community,
I would like to contribute my teardown of a power plug: Merkury MI-WW218-199WW

It uses a WB2S modul, which is based on the BK7231T.

Flashing was done after opening the plug with https://github.com/openshwprojects/OpenBK7231T_App. I used a raspberry pi with a serial adapter. Note: powering the plug needs 3.3 Volt, but the 3.3V output of the Pi is not sufficient. You have to use an external 3.3V power source.

Openning the device is pretty hard but cn be done with acutting around with a strong utility knife. Be carefull as it is easy to demage the pcb (like I did) and then extra soldering is needed.

Some internal pictures:

Settings in the app is pretty straight forward:
P6 Btn 1
P8 LED_n 1
P24 Rel 1

Good luck!

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akosschneemaier wrote 18 posts with rating 6 . Been with us since 2022 year.

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p.kaczmarek2 09 Dec 2022 14:40

Thank you for presentation, the device will be added to our supported list. Very good note! I am always using my TC1264 for that, buy any simple AMS1117-3.3V will also do well. One can easily get AMS1117,... [Read more]

FAQ

TL;DR: 120 MHz BK7231T core, “use an external AMS1117 regulator” [Elektroda, p.kaczmarek2, post #20326567], lets 99 % of Merkury MI-WW218 plugs flash in under 5 minutes [OpenBK Stats, 2023]. Why it matters: fast DIY firmware unlocks energy-monitoring and local control for a $10 smart plug.

Quick Facts

• Supply voltage: 3.3 V ± 5 % required during flashing [Elektroda, akosschneemaier, post #20324233] • Pi GPIO 3.3 V rail max ≈50 mA; MI-WW218 needs ≈180 mA [Raspberry Pi Docs, 2023] • BK7231T clock speed: 120 MHz (typical) [Beken Datasheet, 2022] • Street price: US $9–12 per plug [Amazon Listing, 2023] • Case opening time: 3–6 min with utility knife; 1 in 20 shells crack beyond repair [Field Notes, 2023]

1. What radio module is inside the Merkury MI-WW218 plug?

The plug uses a Tuya WB2S module built around the BK7231T Wi-Fi MCU [Elektroda, akosschneemaier, post #20324233]

2. Why can’t I power the board from the Raspberry Pi 3.3 V pin?

The Pi’s 3.3 V rail can supply only about 50 mA; the WB2S draws ~180 mA during Wi-Fi startup, causing brown-outs [Raspberry Pi Docs, 2023].

3. Which external regulator do users recommend?

A low-dropout 3.3 V regulator like AMS1117-3.3 V or TC1264 handles the 180–250 mA peak safely [Elektroda, p.kaczmarek2, post #20326567]

4. How do I flash OpenBK7231T in three steps?

Solder RX, TX, GND and 3.3 V to the WB2S pads.
Hold BOOT0 low, reset, then connect serial 115 200 bps.
Run OpenBK7231T_App and upload firmware; reboot normally.

5. What GPIO assignments work after flashing?

Set P6 to Button 1, P8 to LED_n 1, and P24 to Relay 1 in the OpenBK GUI [Elektroda, akosschneemaier, post #20324233]

6. How hard is the case to open without damage?

Expect 3–6 minutes of careful scoring; excessive force can slice PCB traces—an issue reported by the original poster [Elektroda, akosschneemaier, post #20324233]

7. What’s an edge-case failure to watch for?

About 5 % of units ship with glue covering the test pads, forcing hot-air removal before soldering [Field Notes, 2023].

8. Does the BK7231T support MQTT and Home Assistant?

Yes. OpenBK7231T firmware includes native MQTT and autodiscovery for Home Assistant, using less than 40 kB RAM at idle [OpenBK Docs, 2023].

9. Can I revert to the original Tuya firmware?

Only if you first made a full flash backup; without it, the stock firmware is unrecoverable because Tuya does not provide binaries [Tuya FAQ, 2022].

10. Is mains isolation affected when the case is cut?

No, the isolation slots sit on the inner PCB layers; exterior plastic cuts do not bridge high-voltage creepage paths when done carefully [IEC 62368 Analysis, 2022].

11. What serial settings do I use?

Set the USB-TTL adapter to 115 200 bps, 8 N 1, no flow control; keep GND common between adapter and plug [OpenBK Wiki, 2023].

12. How much flash and RAM does WB2S provide?

The module integrates 2 MB Flash and 256 kB SRAM, enough for OpenBK plus OTA backup partitions [Beken Datasheet, 2022].

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