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Teardown: SONOFF Smart Switch (Basic)

Recently I purchased a few Smart switches available in the market to see how they are designed and which all ICs are used to make low cost and reliable (many are not).

I have shared high resolution images with details about each section and my observations, hope you will enjoy it and learn something new from this teardown blog.

Smart switch comes with a nice plastic enclosure, outer finish is really good, although I was expected much smaller size.

one side AC Input terminals are there and other side terminal for connecting load (AC light or other equipment).

Good to see they have give plastic plate for each terminal for safety.

PCB is just sitting inside and there are no screws used, fits in with top and bottom enclosure.

On the top side of the PCB, you see MOV for over voltage protection, Line Filter for noise reduction and then a typical AC to DC converter circuit for 230V AC to 5V DC conversion.

One LED is provided to show whether switch is ON or OFF and switch is also given.

10A relay is used for AC switching.

On the back side of the PCB, you see a bridge rectifier diode, BR1.

U2 is 5V DC to 3.3V Linear regulator, Mosfet Q1 is used for operating 5V relay.

They have used Espressif’s ESP8285 Wireless SoC for Wi-Fi connectivity, it has inbuilt RAM and 1MB Flash which is good enough for a smart switch and many other low end applications. In bulk I am guessing it will cost barely 50 cents.

Wi-Fi PCB antenna is visible at the left bottom corner of the PCB.

They have provided slot cuts on the PCB to increase creepage for high voltage area isolation from low voltage circuit.

One of the relay output track is on PCB and to increase current handling capability green mask is removed and solder is accumulated. This is typical in many power electronics PCBs.

another power connection is coming via thick wire connecting two points of the PCB and going to the output terminal. This was quite weird as it is just hanging and a safety concern.

Various ICs used are:

  1. Bridge Rectifier(BR1): ABS8
  2. LP3669(U1): AC to DC Converter
  3. 6211A: 2050/33: 3.3V regulator
  4. ESP8285 Wi-Fi SoC (Espressif)

So, what were you expecting inside a Smart switch?

If you have any questions please ask in the comments section below, I will try to respond as soon as possible.

You can read other teardown blogs and watch teardown videos.

I am currently working as an embedded systems design consultant and helping companies build custom embedded products, develop test automation solution for their PCB or complete product.

If you have any feedback about the blog, you can share in the comments below or you can also contact me directly.

Read more interesting articles on Embedded Systems Design.

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