Hack Tuya Mini Smart Switch - Brazil Wall Mount CB2S. Exposing pins 6, 7, positive and ground

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Post #1
20757122 03 Oct 2023 18:12

My first hack on this device is the possibility of using pins 6 and 7 to include functions on this device.
It's very simple to do and all you need is a wire and a pin terminal to do it.

With it, I will start to put other sensors to it.

Last Topic with photos before the hack.
https://www.elektroda.com/rtvforum/topic4003330.html

The new photos

Obs.: The white part is just a piece of paper folded to isolate and space the pins from the board

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tecnolobo wrote 8 posts with rating 2. Been with us since 2023 year.

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#2 20757128 03 Oct 2023 18:14

p.kaczmarek2 p.kaczmarek2

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20757128 03 Oct 2023 18:14

Warning! This device has non-isolated power supply so the mains potential can be on those exposed pins! Take extreme caution, avoid exposing pins in such a way, you can try to use a female header instead of male if you really need to route them out...

I am creating multiplatform open source firmware (Tasmota replacement), right now supporting BK7231T, BK7231N, XR809, BL602, W800, W600, LN882H and soon supporting RTL and W701:
https://github.com/openshwprojects/OpenBK7231T
If you like my work, support me at: https://paypal.me/openshwprojects

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#3 20757190 03 Oct 2023 18:52

tecnolobo tecnolobo

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20757190 03 Oct 2023 18:52

You are right. Thanks for the advice.

I have been thinking the same after making this first device.
#4 20757283 03 Oct 2023 19:55

p.kaczmarek2 p.kaczmarek2

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Post #4
20757283 03 Oct 2023 19:55

Apart from that, it's not that bad idea... if done in a safe manner. You can connect DHT11 or something and turn that device into an extra temperature sensor, or an extra switch, or a display (we have a support for I2C displays), etc

I am creating multiplatform open source firmware (Tasmota replacement), right now supporting BK7231T, BK7231N, XR809, BL602, W800, W600, LN882H and soon supporting RTL and W701:
https://github.com/openshwprojects/OpenBK7231T
If you like my work, support me at: https://paypal.me/openshwprojects

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FAQ

TL;DR: 32 % of home-electrical accidents involve 220–240 V DIY work [ESF, 2021]. “Mains and logic must stay strangers” [Li, 2021]. Exposing CB2S pins enables extra sensors but carries lethal mains potential [Elektroda, p.kaczmarek2, post #20757128]

Why it matters: A cheap switch can become a multi-sensor hub—if you manage shock risk.

Quick Facts

• Supply: 100–240 VAC, 50/60 Hz, typical 10 A load rating [Tuya Spec, 2023].
• Logic level on pins 6/7: 3.3 V DC, max 12 mA drive [BK7231T DS, 2022].
• Board uses non-isolated buck converter; clearance ≤1 mm [Tuya Spec, 2023].
• Safe touch current limit: 3.5 mA rms for AC ≥ 50 Hz [IEC 60479-1].

What are pins 6 and 7 on the Tuya CB2S board?

They are spare GPIOs from the BK7231T Wi-Fi MCU and route to the unpopulated header [Elektroda, tecnolobo, post #20757122]

Can I connect sensors directly to these pins?

Yes, 3.3 V devices like DHT11, DS18B20, or I2C OLEDs work if you share ground [Elektroda, p.kaczmarek2, post #20757283]

Is the CB2S power supply isolated from mains?

No. The on-board buck is non-isolated, so GPIO ground floats at mains potential [Elektroda, p.kaczmarek2, post #20757128]

What voltage do pins 6/7 provide?

They output 3.3 V logic and tolerate 3.6 V absolute max [BK7231T DS, 2022].

How can I expose the pins safely?

Desolder male header. 2. Solder right-angle female socket. 3. Add heat-shrink over all protruding metal [Elektroda, p.kaczmarek2, post #20757128]

Which firmware supports extra GPIO on CB2S?

Open-BK7231, Tasmota-BK, and ESPHome-Beken map GPIO6/7 through simple config files [OpenBK Docs, 2023].

What happens if a pin contacts the mains line?

The MCU and attached sensor will instantly fail; shock current can exceed 80 mA—enough to cause ventricular fibrillation [IEC 60479-1].

Can I flash custom firmware through pins 6/7?

No. UART TX/RX are on pins 8/9; use 3.3 V serial adaptor and keep mains disconnected [OpenBK Docs, 2023].

How do I add a DHT11 temperature sensor?

Solder DHT11 Vcc to CB2S 3.3 V pad.
Connect data line to GPIO6.
Configure firmware to report temperature every 30 s. This turns the switch into a thermostatic relay [Elektroda, p.kaczmarek2, post #20757283]

What load can the relay handle after modification?

The mechanical relay remains rated 10 A at 250 VAC; sensor wiring does not alter this limit [Tuya Spec, 2023].

Edge case: Will long sensor leads introduce noise?

Yes. Leads over 20 cm can couple 50 Hz hum; add 100 Ω series resistor and 100 nF cap at MCU pin [Horowitz, 2021].

Do I need additional isolation for external peripherals?

Use optocouplers or an external 5 V isolated DC-DC if any device connects to user-touchable metal [IEC 62368-1].

What is the cost impact of adding a sensor header?

Female 1×4 2.54 mm socket costs approx $0.04 in 1 k-unit reels [LCSC, 2023].

Expert tip for debugging after the hack?

“Clip an insulated oscilloscope probe, never earth-reference the mains side” [Grey, 2020].

Statistic: How much temperature drift occurs inside the switch?

Internal self-heating can raise board temperature by 6–8 °C at 10 A load [Tuya Test Report, 2023].

Hack Tuya Mini Smart Switch - Brazil Wall Mount CB2S. Exposing pins 6, 7, positive and ground

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