FAQ
TL;DR: 80–85°C reported on FS-02HW is unusually high [Elektroda, groove6j, post #21438473] "The second RX2 is a silkscreen error" [Elektroda, p.kaczmarek2, post #20595325] Use RX1/TX1; flash as BK7231N; 2MB backup [Elektroda, p.kaczmarek2, #20595325; #20639767].
Why it matters: This FAQ helps makers reliably flash CB2S (BL2028N) modules, fix pinout confusion, and troubleshoot heat on Aubess FS‑02HW/FS‑02WE.
Quick Facts
- Module: CB2S (BL2028N) behaves as BK7231N for flashing; use RX1/TX1 for UART; UART2 is debug at 115200 baud (not for flashing) [Elektroda, p.kaczmarek2, #20595325; #20639767].
- Silkscreen errors are common: RX/TX labels can be swapped; follow Tuya pinout, not the print [Elektroda, p.kaczmarek2, #21086488; Pete0815, #21086597].
- Backup size: make a full 2MB dump; the OpenSHWProjects flasher can extract GPIO config from it [Elektroda, p.kaczmarek2, post #20595325]
- Reported temps: FS‑02HW modules read ~80–85°C vs ~40–50°C on other minis; relay heat suspected [Elektroda, groove6j, #21438473; #21440741].
- Reliable flashing flow favors desoldering and a power-sequence over CEN shorting [Elektroda, p.kaczmarek2, post #21086320]
What chip is inside the Aubess FS-02HW and which pins do I use?
FS‑02HW uses a CB2S module with BL2028N (BK7231N-family). Flash via RX1/TX1; UART2 (TX2/RX2) is debug only. Silkscreen on many CB2S boards is wrong—ignore duplicate RX2 or swapped labels and follow the Tuya pinout image [Elektroda, p.kaczmarek2, #20595325; #21086488].
I see two RX2 labels—how do I wire it correctly to flash?
It’s a silkscreen error. Use RX1/TX1 for the flasher; TX2/RX2 is debug. Several users succeeded after swapping to the documented pinout despite the board text. “The correct pinout is always at the Tuya site.” [Elektroda, p.kaczmarek2, #20595325; #21086488; Pete0815, #21086597].
How do I flash OpenBeken onto a CB2S (BL2028N) reliably?
Pick BK7231N in the OpenSHWProjects BK7231GUIFlashTool, not BK7231T. Make a 2MB backup first, then write OpenBeken. Follow the Tuya pinout for RX1/TX1 and 3.3V/GND [Elektroda, p.kaczmarek2, #20639767; #20595325].
What’s a proven 3-step flashing sequence if CEN shorting fails?
- Desolder CB2S; wire RX, TX, GND; prepare 3.3V but leave it disconnected.
- Start flashing in the tool; momentarily short the module’s 3.3V line to GND (not the PSU).
- Connect 3.3V from PSU to the module; flashing should begin [Elektroda, p.kaczmarek2, post #21086320]
The flasher shows no bus activity—what should I check first?
Check that RX/TX isn’t swapped (common on misprinted CB2S). Ensure your USB‑UART plus regulator can supply stable 3.3V. Prefer desoldered flashing and the power-sequence. Users fixed detection by ignoring silkscreen and using the Tuya pin map [Elektroda, p.kaczmarek2, #21086488; #21086320; Pete0815, #21086451; #21086597].
What output should I see on TX2 during boot, and at what baud?
TX2 (UART2) emits debug at 115200 baud. Some modules only spew non-ASCII bytes; when CEN is held low, the stream stops. That’s normal for debug and not used for flashing [Elektroda, p.kaczmarek2, #20595325; Weafyr, #20600738; fabcia, #20642343].
Can BL2028N be flashed like BK7231N?
Yes. Select BK7231N in the flasher. Community reports confirm BL2028N is flashable, and successful flashes were done after correcting the pinout wiring [Elektroda, p.kaczmarek2, #20639767; Pete0815, #21086597].
Is there an edge case where UART flashing won’t work at all?
One user suspected a missing bootloader region (0x00000000–0x11000 ≈ 68KB), causing no UART functionality. If TX2 shows only noise and the flasher never syncs, SPI reprogramming would be needed, but CB2S lacks SPI pads; transplanting to ESP8266 is a fallback [Elektroda, fabcia, #20639729; p.kaczmarek2, #20639767].
My FS-02HW reads 80–85°C idle. Is that normal and how do I debug it?
That’s abnormally high; other mini switches read ~40–50°C. Swap the Wi‑Fi module to isolate heat source; one user found the relays themselves run hot even with no load, pointing to the PCB/relay, not CB2S [Elektroda, groove6j, #21438473; p.kaczmarek2, #21438559; groove6j, #21440741].
Does the FS-02WE with power metering wire BL0937 over UART?
No. BL0937 isn’t a UART device; it uses three GPIOs: SEL, CF, CF1. Confusion comes from BL0942, which supports UART or SPI. Lack of RX/TX wiring to BL0937 is expected [Elektroda, p.kaczmarek2, post #20639185]
What tool should I use and what size backup is recommended?
Use the OpenSHWProjects BK7231GUIFlashTool. Make a full 2MB backup; it can auto-extract the GPIO template from that dump for easy OpenBeken setup [Elektroda, p.kaczmarek2, post #20595325]
Can I flash CB2S in-circuit, or should I desolder?
In-circuit can fail due to power path and interference. The maintainer recommends desoldering and using the power-sequence method for reliable sync and write [Elektroda, p.kaczmarek2, #21086320; Pete0815, #21086451].
Is ESP‑02S a drop‑in replacement for CB2S in these switches?
Yes. ESP‑02S shares the pinout and can replace CB2S directly. Users confirmed swap success after using the correct CB2S/ESP02S pin map instead of faulty silkscreen [Elektroda, Pete0815, #21085368; #21086597; fortunatornforty76, #21332287].
Any expert tip to avoid the common pinout trap?
“The markings can be ignored. They are a human error.” Always wire to the Tuya-documented CB2S pad order, not what’s printed on your module [Elektroda, p.kaczmarek2, #21086488; #20595325].
What if UART2 shows bytes but the flasher still won’t connect?
That can be normal; UART2 is debug only. Re-check that you’re on RX1/TX1, not RX2/TX2, and that your adapter supplies stable 3.3V. If still blocked, desolder and use the power-sequence [Elektroda, p.kaczmarek2, #20595325; #21086320; Weafyr, #20600738].
