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

p.kaczmarek2 7098 37

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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  • #31 21361708
    p.kaczmarek2
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    Here are mine:
    Various prototype boards and electronic modules on a wooden surface. A hand holding an electronic device with an LCD display module.
    I am thinking about using them with Wemos D1 converted to BK7231
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  • #32 21361714
    divadiow
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    ah i see. shields are hats, extensions, add-ons. of course :)
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  • #33 21362685
    p.kaczmarek2
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    Those markings are so misleading:
    Two NodeMCU modules with pin labels visible on a dark background.
    I wonder how hard would it be to make a custom build (or a skin, or a script?) of OBK that will have NodeMCU-style pin names next to classic pin names...
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  • #34 21362718
    divadiow
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    interesting idea. Almost daily I'm referring to some mapping image on here or one I've made for various modules/ESP adaptors. Even some kind of basic ASCII selection to map choice1<->choice2. dunno
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  • #35 21362780
    p.kaczmarek2
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    Ok, so here is initial draft:
    https://openbekeniot.github.io/webapp/test1.html
    Open link and hover mouse cursor over pin name to higlight it.
    That's how it looks like:
    NodeMCU board diagram with highlighted GPIO pins.
    Next step would be to integrate it into pins chooser and GPIO doctor, I guess?
    Who knows html and js? @max4elektroda ? But maybe I will try to do it first myself. Keep the canvas and stuff as separate JS module on web app. Fetch it from web on pins page load. Allow user to select his board type, so NodeMCU, raw CB3S, etc, etc.

    Added after 3 [hours] 14 [minutes]:

    I added drawing handles:
    NodeMCU board pin diagram with highlighted pins.

    Added after 49 [minutes]:

    something like this, maybe?


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  • #36 21363276
    max4elektroda
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    That's really a very useful feature to easily identify the pins. Thanks!
    p.kaczmarek2 wrote:
    Who knows html and js? @max4elektroda ? But maybe I will try to do it first myself.

    You don't even allow some time to read before you present a nice realization ;-)
  • #37 21363284
    p.kaczmarek2
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    I think I may get initial version working soon, but we will need to create our own "boards.json":
    ESP32 board pin diagram with a dropdown list for board selection.
    And there is also question where would we store board information, but since it's not a critical piece of information, I may just decid to store it in Cookie so it's a developer only feature remembered by current browser? Idk.... or add a command for that
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  • #38 21364328
    p.kaczmarek2
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    Recently I've did a very simple classic CB2S to NiceMCU transplant: CB2S/WB2S cheap dev board made from NiceMCU_WB3S_V1 (replace WB3S with WB2S/etc) . It might be good idea for anyone looking for cheap CB2S/WB2S dev boards, as NiceMCU is very cheap (as low as 1$ for new clients) and with my approach, the pin indexes on silkscreen are not mixed after conversion.
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Topic summary

✨ The discussion centers on converting a cheap NodeMCU ESP8266 development board into a BK7231 development board by transplanting a BK7231 WiFi module (CB3S or WB3S) onto the NodeMCU PCB after desoldering the original ESP12 module using a hot air station. This method offers a cost-effective and flexible alternative to buying dedicated BK7231 dev boards, especially for users who have BK7231 modules salvaged from IoT devices. Key tools include a hot air station and basic soldering equipment, with some users exploring alternative heating methods like dual soldering irons due to lack of a heat gun. The transplant process involves careful desoldering, pad cleanup, and pin mapping verification, with some discussion on correcting pinout diagrams for I2C lines (S3, SK, SC) to ensure sensor compatibility (e.g., BMP280, AHT20). UART logging configuration is also addressed, recommending UART1 for logging due to CH340 USB interface connection. Additional topics include testing of TM1638 displays, power cycling via CEN or reset buttons, and the use of ShiftRegister for driving more LEDs. The community also explores software tools for pin mapping visualization and integration with OpenBK firmware. Alternative inexpensive boards without pre-soldered ESP modules are noted as options to avoid destructive desoldering. The conversation extends to related modules and development boards such as BK7238 NiceMCU, WEMOS W1F1 D1, and various BK series modules (CB2S, WB2S, CB3L, etc.), with interest in Arduino shield compatibility and custom firmware adaptations.
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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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