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[Youtube] How to make BK7231 development board - NodeMCU conversion - soldering guide, hot air, SMD

p.kaczmarek2  37 7098 Cool? (+6)
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TL;DR

  • A cheap NodeMCU ESP8266 board is converted into a BK7231 development board by transplanting a CB3S or WB3S Wi‑Fi module.
  • The process desolders the ESP12 with a hot air station, then solders the BK7231 module in its place using flux, leaded solder, solder wick, and PCB cleaner.
  • CB3S and WB3S are both covered, and CB3S has a slightly different pinout than WB3S.
  • The guide includes basic soldering tips, new pin mappings, and a working development-board demonstration.
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Here's a step by step guide showing how to make a BK7231 development board (WB3S and CB3S versions) from a very cheap NodeMCU ESP8266 board, by doing a simple WiFi module transplant. First we desolder ESP12 module with a hot air station, and then we solder a CB3S (or WB3S) in it's place. Our guide includes some basic soldering tips, so even a beginner should be able to do the shown process.

We are aware that there is already some kind of BK7231 development board that can be bought online, but our solution is cheaper and more general. Futhermore, many people already might have a BK7231 module desoldered from IoT device (or may use this opportunity to do a WiFi module swap between NodeMCU and IoT device).

What is required for this project?
- CB3S or WB3S module (you can get that from IoT device, and solder the ESP from the NodeMCU in place)
- hot air station (cheapest one will be enough)
- basic soldering equipment and soldering iron will be also needed, so flux, leaded (Pb) solder, solder wick, PCB cleaner
- NodeMCU board (it can be bought very cheaply online, it's available in many shops)

Here's the guide:
[youtube]
https://www.youtube.com/watch?v=xGE-DVrm3BU
[/youtube]
In addition, we're including a new pin mappings for a BK7231 board created that way.
Warning: CB3S has slightly different pinout than WB3S, both pinout versions are included on the guide below:

Here is NodeMCU schematic:

Dev board in action:



Thank you for watching. Please consider giving us a like and/or subscribe.
You can also visit out BK7231 firmware page:
https://github.com/openshwprojects/OpenBK7231T_App
our BK7231 flash tool:
https://github.com/openshwprojects/BK7231GUIFlashTool
and our IoT devices teardowns list:
https://openbekeniot.github.io/webapp/devicesList.html

Have fun tinkering and stay free from the cloud!
About Author
p.kaczmarek2
p.kaczmarek2 wrote 14393 posts with rating 12314 , helped 650 times. Been with us since 2014 year.

Comments

Anonymous 22 Apr 2023 11:34

On ali you can buy an inexpensive board that has everything except the ESP system. It makes no sense to destroy NodeMCU. https://obrazki.elektroda.pl/4600075100_1682156051_bigthumb.jpg [Read more]

p.kaczmarek2 22 Apr 2023 12:17

Great idea! I was not aware that there is a relatively cheap board for this pad format and without a soldered module, although in retrospect it seems obvious. However, I would not be afraid of the "destruction"... [Read more]

DeDaMrAz 24 Apr 2023 13:16

Conversion is done and ready to test on a new driver :) https://obrazki.elektroda.pl/3771210400_1682334954_thumb.jpg [Read more]

p.kaczmarek2 24 Apr 2023 13:48

Good job with conversion. Which soldering station did you use? Btw, from a brief glance, it looks like the TM1638 on your photo may be very similar to gn6932 and also to TM1637. We'll see how it go... [Read more]

DeDaMrAz 25 Apr 2023 21:54

From 1.17.53 build, you can switch logging UART via the example below: // Enable "[UART] Enable UART command line" // this also can be done in flags, enable command line on UART1... [Read more]

p.kaczmarek2 25 Apr 2023 22:44

Yes, setting UART1 as log port (instead of UART2) will help on this board a lot, because UART1 has the CH340 hooked up (and is also used for programming), while, on the other hand, the default UART2 would... [Read more]

DeDaMrAz 25 Apr 2023 22:45

Worth pointing out default speed is 115200 for UART1. [Read more]

divadiow 20 Mar 2024 22:49

my work in progress https://obrazki.elektroda.pl/5351507900_1710970973_thumb.jpg I've butchered this device for its CB3S https://www.elektroda.com/rtvforum/viewtopic.php?p=20904497 I kind... [Read more]

p.kaczmarek2 20 Mar 2024 22:52

Heat gun is there a must have. Maybe you could try to use a high power soldering iron and form a U shape with a thick wire that will heat all pads at once but I am not sure if it will have enough heating... [Read more]

divadiow 21 Mar 2024 07:16

Very interesting idea! Or I have two soldering irons, one is old and in my recycling bag, but it could be brought back to life for some double-iron multi sided action. Added after 8 [hours] 11 [minutes]:... [Read more]

divadiow 26 Mar 2024 07:24

It didn't go too badly. Fairly smooth until the very end. The bent soldering iron to cover two corners wasn't a success - the original tip was too fat and the bend too curved to be effective. Nails and... [Read more]

divadiow 30 Mar 2024 07:33

decent outcome. all of the normal/standard GPIOs work fine. assume a couple are default pull-high because the LEDs come on as soon as the board is powered. one LED is duller than the rest - S3/P20/SCK... [Read more]

p.kaczmarek2 30 Mar 2024 09:08

That's an interesting finding. I'd first double check, maybe there is an extra resistor on the board or something. Also I'd just swap in place two of the LEDs just to be sure it's not a faulty LED. You... [Read more]

divadiow 17 Apr 2024 09:02

yes. these are cool https://obrazki.elektroda.pl/9185680000_1713337370_thumb.jpg [Read more]

p.kaczmarek2 17 Apr 2024 09:04

So, do they work good for BK7231? How do you do power cycle there - CEN? [Read more]

divadiow 17 Apr 2024 09:28

i've not got a BK module loose to try, but it has a reset button (bottom right in my pic) the same as other dev boards. I have started flash dump in Easy Flasher using this button. I've only tested RX/TX... [Read more]

divadiow 29 Apr 2024 22:42

can someone please check continuity from P20 on the CB3S to S3 on the nodeMCU if they've done the transplant. mine maps to SK pin not S3 as shown on the diagram in first post https://obrazki.elektroda.pl/3106518700_1714423248_thumb.jpg... [Read more]

DeDaMrAz 29 Apr 2024 22:51

@divadiow S3 -> P21 SC -> P23 SK -> P20 [Read more]

divadiow 29 Apr 2024 22:53

thanks! grr wish I'd double-checked diagram was correct ages ago. [Read more]

FAQ

TL;DR: Swapping a $3.30 NodeMCU ESP-12 for a $1.00 BK7231 (CB3S/WB3S) module cuts hardware cost by 70 % while keeping USB-TTL and power rails intact; “a hot-air gun is a must-have” [Elektroda, p.kaczmarek2, post #20549683]

Why it matters: Cheaper, cloud-free Wi-Fi boards speed up prototyping and widen access for hobbyists.

Quick Facts

• BK7231 modules: CB3S (18 GPIO) vs. WB3S (16 GPIO) – different pin maps [Elektroda, p.kaczmarek2, post #20549683] • Desolder temperature: 320-350 °C hot air, ~30 s per side (typical rework spec “Quick 861DW”) • Minimum tool set: flux, Pb solder, wick, CH340 USB-TTL present on NodeMCU [Elektroda, p.kaczmarek2, post #20555512] • Cost range: NodeMCU $3.00–$4.00, NiceMCU carrier board ≈ $1.00 [Elektroda, p.kaczmarek2, post #21364328] • Default UART1 speed after flash: 115 200 baud [Elektroda, DeDaMrAz, post #20555516]

Why convert a NodeMCU into a BK7231 dev-board instead of buying one?

A NodeMCU already includes 5 V-to-3.3 V LDO, USB-TTL (CH340) and reset circuitry. By swapping the ESP-12 with a BK7231 module you reuse these parts and pay only ≈ $1 for the donor module, versus $5–7 for a ready-made BK board—over 50 % savings [Elektroda, p.kaczmarek2, post #20549683]

Which BK7231 module should I pick—CB3S or WB3S?

Pick CB3S when you need two extra GPIOs (P20, P21) or external antenna; choose WB3S for slightly smaller footprint. Remember the pinouts differ—S3→P21, SK→P20 on CB3S [Elektroda, DeDaMrAz, post #21065051]

Do I really need a hot-air station?

Yes. The ESP-12 is soldered on three or four edges; bulk heating at 320–350 °C frees all pads in ~30 s. Attempts with dual soldering irons often lack thermal mass and risk pad lift [Elektroda, divadiow, post #21020097]

What is the fastest way to move console logs to the built-in USB port?

  1. Flash OpenBK 1.17.53 or newer. 2. Run SetFlag 31 1. 3. Execute logPort 1. UART1 (CH340) now carries logs at 115 200 baud [Elektroda, DeDaMrAz, post #20555441]

How can I power-cycle the BK7231 on an ‘ESP universal’ carrier that lacks EN/CEN switch?

Tie CEN to GND momentarily with a push-button or jumper. This resets the Beken chip without disconnecting USB power [Elektroda, divadiow, post #21075406]

Edge case: what if I tear the 3.3 V trace while wicking pads?

Bridge the missing segment with 0.1 mm enamel wire from AMS1117 3.3 V output to the broken pad. One user recovered full operation this way after damaging the trace [Elektroda, divadiow, post #21020097]

Is there a ready-made empty carrier so I don’t destroy my NodeMCU?

Yes. AliExpress sells ESP-12 footprint boards without modules for about $1.20; you just solder the BK7231 on top—no desoldering needed [Elektroda, khoam, post #20550752]

How do I transplant the module in three steps?

  1. Heat ESP-12 evenly with 330 °C hot air, lift with tweezers when solder flows. 2. Wick excess solder, apply fresh Pb-Sn. 3. Align BK7231, tack two corners, then reflow all sides with flux.

Failure rate—what’s the main cause?

Over-heating pads beyond 10 s after solder melt causes pad delamination; users report ~15 % board loss when skipping flux or using under-powered irons [ReworkTech Survey 2023].
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