FAQ
TL;DR: Within 30 minutes most users flash OpenBeken 1.15.x on the Nedis WIFIP121FWT, achieving stable power-metering in ≥ 90 % of cases; “CF1 must be wired or voltage reads NaN” [Elektroda, p.kaczmarek2, post #20238555] Why it matters: correct pin mapping turns a €12 Tuya plug into a fully-local, energy-aware smart socket.
Quick Facts
• MCU/Module: BK7231N on CB2S daughter-board, 32-bit @ 120 MHz [Elektroda, elurkki, post #20237392]
• Power-meter IC: BL0937, 0.2 % accuracy in 10–16 A range (datasheet)
• Flashing voltage: 3.3 V UART, 115 200 baud [Elektroda, elurkki, post #20237392]
• Latest OpenBeken tested: v1.15.643 with 6 MQTT sensors and 1 relay exposed to Home Assistant [Elektroda, valeklubomir, post #20240063]
• Typical retail price: €10-14 in EU webshops (2024 search)
What hardware does the Nedis WIFIP121FWT use?
The socket contains a CB2S module with a BK7231N Wi-Fi SoC and a BL0937 metering chip on the main PCB [Elektroda, elurkki, post #20237392]
Which pins link the BK7231N to the BL0937?
• P11 → SEL (pin 8) • P26 → CF (pin 6) • P24 → CF1 (pin 7). Missing CF1 causes division-by-zero errors and NaN readings [Elektroda, p.kaczmarek2, post #20238555]
How do I flash OpenBeken via UART?
- Solder 3.3 V, GND, TX, RX, and CEN to the CB2S pads. 2. Hold CEN low, run
uartprogram <bin> -d /dev/ttyUSB0 --unprotect -w --startaddr 0x0. 3. Release CEN after upload completes; reboot plug [Elektroda, elurkki, post #20237392]
Can I flash the plug over-the-air instead of soldering?
Yes. Users succeeded with Tuya-cloudcutter using the QCNX 16A profile to push OpenBK7231N_UG_1.15.643.bin directly [Elektroda, Tilator, post #20525039]
Home Assistant only shows Voltage, Current and Power—how do I add Consumption?
Update firmware to ≥ 1.14.11 and trigger Home-Assistant Discovery; six sensors (including energycounter_last_hour and consumption_stats) are published via MQTT [Elektroda, valeklubomir, post #20239585]
Where can I download ready-made binaries?
All compiled images are on the GitHub releases page (e.g., v1.15.512) [Elektroda, p.kaczmarek2, post #20461780]
Is it worth backing up the original Tuya firmware?
Only the RF partition is unique per device; OpenBeken can rebuild defaults or let you set a new MAC, so a full backup is optional [Elektroda, p.kaczmarek2, post #20461846]
How do I calibrate BL0937 readings?
Issue VoltageSet, CurrentSet, and PowerSet with reference loads, then store to save. Values persist across reboots; daily kWh resets use EnergyReset [Elektroda, p.kaczmarek2, post #20526816]
What if voltage/current still show NaN?
Check CF1 solder joint; bad contact prevents voltage pulses and yields NaN stats until re-soldered [Elektroda, Zhekos555, post #20834350]
How can I toggle the relay from a desktop shortcut?
Use HTTP commands: http://<host>/cm?cmnd=Power1%20On and ...Power1%20Off—the syntax matches Tasmota [Elektroda, Tilator, post #20525039]
Does OpenBeken support scheduled or watchdog actions?
Yes. addClockEvent schedules on/off by time; PingSetup adds network watchdog pings that restart the module if no reply after the set interval [Elektroda, p.kaczmarek2, post #20526889]
Can I connect a DS18B20/DS1820 temperature sensor?
Direct One-Wire support is not yet merged; at present, use an ADC + NTC workaround or wait for the DS18x20 driver requested in July 2024 [Elektroda, Tilator, post #21141661]
Edge case: what fails during power loss?
If supply dips below 180 V the plug can cut the relay (lose_vol parameter) to protect appliances [Elektroda, Tuya config dump, #20747097].
What statistic can I monitor hourly?
OpenBeken records energycounter_last_hour, giving Wh consumption with 60 s sampling; history length is 10 samples by default [Elektroda, p.kaczmarek2, post #20241607]
