TEARDOWNS

# Belkin WeMo Teardown

## Overview

The Belkin WeMo is a home automation product that works as a smartphone controlled power interrupter for standard electrical outlets.

Following are some brief stats about the product:

 Model Num: F7C027au WeMo ID WeMo.781 Serial Number 221307K11000781 Driver MAC EC1A59799F61 Input 240V, 10A Output 240V, 10A

The screws are triangle (anti-tamper), 2.3mm. 2 of the four are hidden underneath the back sticker, which has to be cut before you can open it.

There are two PCBs, with a 3-wire connector between them. One can bet that the three wires are logic power, ground, and relay on/off control. 1 contains all the power circuitry, one the low-voltage logic.

## Power PCB

They use a mechanical relay to switch the mains to the outlet. The relay is the HF3FA (005-HTF, SM47C), and is rated for 250VAC at 10A. As you would expect, it switches the live wire, ground and neutral are connected permanetly to the output.

The low-voltage rails for the logic board look to be generated by a transformer, diode (only a single one, not a bridge!) and capacitor arrangement from the 240VAC. The transformer has the number OEM-EPC130305001 GP on it.

For protection, there looks to be a thermal PTC fuse (VR1), with something that looks like an LED taped to the side of it. This kind of looks like a post-PCB design hack, maybe they added the ability for the LED to go on if the PTC fuse triggers?

There is also an inductory looking thingy (L3), which I think could be EMI filtering for the logic level power rail (it is right next to the connector).

## Logic PCB

The main chip on this board is the Ralink RT5350F (other numbers on the IC are TPMX249409, 1246PTA1). This is a combined wireless front-end (1T1R 2.4G CMOS RF), stack (802.11n 1T1R MAC/BBP) and embedded CPU. I had a quick look on on AliExpress.com, and they seem to sell for about US$2.90, in quantities of 5 (Jan 2014). This is cheap (really cheap)! DigiKey nor any other non-Chinese supplier (try www.findchips.com) did not seem to stock these. Notice in the above picture that there is a PCB antenna in the upper-right corner of the PCB (when looking from the front of an assembled device, so upper-left in the image). On the other side of the board are two more ICs, the Winbond W9825G6JH-61 1302P 62267700003 (166MHz 256MB SDRAM TSOP 54-pin 0.80mm pitch IC), which was available on DigiKey for US$3.23 (1) and US$2.33 (1000). The other IC is a Macronix (MXIC) MX25L12835EMI-10G, which is 128Mbit, 104MHz SPI flash memory. This sells for US$3.35 (1) and US2.42 (1000) on DigiKey.

There is also a miniature switch on the reverse-side of the PCB (inaccessable to the user).

Another tear down for the Belkin WeMo exists at OpenWrt.