FAQ
TL;DR: After flashing a BK7231N/CB2S, no AP plus a dim blue LED often means a boot or wiring issue; AP current is typically 50–80 mA, and “Log on TX2 should be @ 115200.” [Elektroda, DeDaMrAz, post #21720037]
Why it matters: This FAQ helps makers fix "flashes OK but no AP" on BK7231N smart modules, fast.
- Typical AP-mode current draw: 50–80 mA (module only, no relay). [Elektroda, DeDaMrAz, post #21720037]
- CB2S module uses the BK7231N SoC; Wi‑Fi LED often on P8 by default. [Elektroda, philip3, post #21718054]
- UART debug: TX2 at 115200 baud; capture on bench power only. [Elektroda, DeDaMrAz, post #21720037]
- Boot enable (CEN) must not be tied to GND; check before troubleshooting. [Elektroda, DeDaMrAz, post #21718123]
- Flash device seen in logs: TH25Q16HB, 2 MB, MID 0x1560EB. [Elektroda, philip3, post #21718685]
Quick Facts
- Typical AP-mode current draw: 50–80 mA (module only, no relay). [Elektroda, DeDaMrAz, post #21720037]
- CB2S module uses the BK7231N SoC; Wi‑Fi LED often on P8 by default. [Elektroda, philip3, post #21718054]
- UART debug: TX2 at 115200 baud; capture on bench power only. [Elektroda, DeDaMrAz, post #21720037]
- Boot enable (CEN) must not be tied to GND; check before troubleshooting. [Elektroda, DeDaMrAz, post #21718123]
- Flash device seen in logs: TH25Q16HB, 2 MB, MID 0x1560EB. [Elektroda, philip3, post #21718685]
Why does my BK7231N flash “success” but show no AP and a dim blue LED?
A successful write can still fail to boot if wiring, power, boot pins, or config are wrong. Check CEN is not grounded, use short UART leads, remove programming wires after flashing, and power the module on the bench. If still no AP after minutes, capture TX2 logs at 115200. [Elektroda, DeDaMrAz, post #21718123]
What current draw should I expect when the module creates its AP?
Expect about 50–80 mA for the module alone in AP mode. Higher current may indicate peripherals; much lower current with a dim LED can indicate a stalled boot. “Log on TX2 should be @ 115200.” [Elektroda, DeDaMrAz, post #21720037]
How do I capture a boot log from TX2 on CB2S/BK7231N?
Use a 3.3 V USB‑UART. Connect GND‑to‑GND, adapter RX‑to‑TX2 pad, and power the module from a bench 3.3–5 V supply (per board). Open your terminal at 115200 8N1 and reset with CEN. “Be extremely careful” and avoid mains during testing. [Elektroda, DeDaMrAz, post #21719334]
Could a bad write corrupt only a few bytes and kill the AP?
Yes. Even a few wrong bytes in firmware or parameters can stop boot. Reflash the backup, then read back and compare files byte‑for‑byte to confirm integrity. Shorter wires and clean power improve reliability during writes. [Elektroda, DeDaMrAz, post #21720082]
My backup works on another module but not mine. What does that imply?
If your backup image boots on a known‑good module, your target hardware is suspect. Damage during handling, ESD, or power mistakes can leave the module unreadable at runtime even if flashing verifies. Consider replacing the module. [Elektroda, DeDaMrAz, post #21720055]
What is the CB2S module and which chip does it use?
CB2S is a Tuya Wi‑Fi module built around the BK7231N SoC. In the shared config, the relay is on P26, button on P24, and Wi‑Fi LED on P8. [Elektroda, philip3, post #21718054]
What flash chip and size does BK7231N report in the logs?
The flasher identified a TH25Q16HB SPI NOR with 2 MB capacity and MID 0x1560EB. Size mismatches or protection bits can block proper writes, so confirm this matches your unit. [Elektroda, philip3, post #21718685]
How long should I wait for the AP SSID to appear after power‑up?
AP SSID should appear shortly after a clean boot. If you waited 30 minutes with no SSID, the device likely failed to boot or remains in a reset state. Check CEN, power, and capture TX2 logs. [Elektroda, philip3, post #21718139]
What is “CEN” and why does it matter here?
CEN is the chip enable/reset pin. If it’s shorted to ground, the SoC stays held in reset and never boots, so no AP appears. Confirm CEN is free and only pulsed for reset during flashing. [Elektroda, DeDaMrAz, post #21718123]
How should I power the board safely while debugging?
Power on the bench using a known, isolated supply. Do not power from mains during serial logging. Keep leads short and remove UART wires after flashing to avoid pin conflicts. “Power the device on the bench.” [Elektroda, DeDaMrAz, post #21719334]
What is “Tuya” in this context?
Here, “Tuya” refers to the original vendor firmware/config that shipped with the device. The user extracted mapping data and backed up this image before flashing. [Elektroda, philip3, post #21718054]
What is OpenBK/OpenBeken in the flasher log?
The image name shows “OpenBK7231N_QIO_1.18.189.bin.” Users commonly replace the stock Tuya firmware with this image on BK7231N modules. It was written while skipping the bootloader area. [Elektroda, philip3, post #21718685]
How do I verify my write actually matched the file? (3‑step check)
- Flash the backup image.
- Read the entire flash back to a file.
- Compare hashes or bytes against the original file; they should match exactly.
[Elektroda, philip3, post #21720075]
What UART and power levels should I use with CP2102 or FT232 adapters?
Use 3.3 V for RX/TX. If you feed 5 V, route it only to the board’s 5 V regulator input, not to the SoC. Confirm grounds are common. Avoid long leads and noisy USB ports. [Elektroda, philip3, post #21720025]
My TX2 output looks like garbage characters. What now?
Garbage often means wrong baud or ground issues. Set 115200 baud, verify GND is solid, and shorten leads. If still unreadable, the SoC may not execute code due to damage or bad flash. [Elektroda, philip3, post #21720025]
When should I give up and replace the module?
If CEN checks out, 115200 TX2 shows no readable log, readbacks verify, and your backup boots elsewhere, the module is likely damaged. Replacing the module saves time. [Elektroda, philip3, post #21720157]
