Teardown Tuesday: IoT Power Outlet
Today demand for IoT devices is rapidly growing. What are inside of an IoT power strip? Find out in this teardown!
Today, demand for IoT devices is rapidly growing. In this Teardown Tuesday, we are going to take a look at a Wi-Fi controlled power outlet.
The particular device used in this article is the WiOn 50049 Outdoor Wi-Fi Outlet.
The IoT outlet
This Wi-Fi outlet has two output plugs, rated at 15 amps, and is intended for outdoor use. In order to unlink some smart home systems that rely on a hub, this device pairs directly to your existing Wi-Fi network.
There are two circuit boards inside of the this IoT device. There is a PCB to handle the switching and regulation of AC voltage. Connected to this board through a three-wire interface is a low voltage board that contains the Wi-Fi module, power switch, and status LEDs.
AC Circuit Board
The top of the AC PCB
The AC circuit board used in this power outlet is a single-sided PCB that contains both through-hole and surface-mount components. On the copper side of the PCB, there is green solder mask and white silk screen. On the non-copper side, there is black silk screen.
The bottom of the AC PCB
In an effort to increase the current carrying ability of the main power traces, solder is applied to the traces. The layer of solder over the copper trace increases its thermal mass. By increasing the thermal mass, the traces heat up less and hot spots on the traces are reduced. Also, there is routing on the PCB to separate the high voltage components.
Solder over the high-current traces
Wi-Fi Circuit Board
The Wi-Fi PCB
The Wi-Fi PCB is a two-layer PCB with surface mount components on one side. This PCB has green solder mask and white silkscreen on both sides. The copper has an ENIG plating on it, giving it a gold appearance.
There are two power supplies located in this device. The first power supply, located on the AC board, converts the 120VAC down to 5VDC. The second power supply, located on the Wi-Fi PCB, reduces the 5v down to 3.3v.
AC to DC Power Supply
The Fremont FT838 IC
Located on the AC board there is an AC-to-DC power supply. The AC-to-DC power supply uses a Fremont Micro FT838NB1-RT IC. This IC controls the voltage regulation and is able to provide current limiting, open circuit detection, over temperature protection, and over voltage protection.
This IC requires quite a few external components but the primary ones are a diode, transformer, and output capacitors. This power supply reduces the voltage from 120VAC to 5VDC to power the Wi-Fi PCB and relay coil.
DC-to-DC Power Supply
The 3.3V linear regulator
The second power supply in this IoT outlet is located on the Wi-Fi PCB. This regulator is a linear regulator that converts the 5VDC generated on the AC board down to 3.3VDC. The regulator used is an LD1117 LDO regulator in an SOT-223 package without any manufacturer's markings.
The Wi-Fi module
In order for this device to be part of the IoT, it needs to be able to connect to the internet! The Wi-Fi module used is manufactured by Kab Enterprise. Kab Enterprise appears to be the actual manufacturer of this IoT power outlet. The module is FCC certified (FCC ID: PAGECO-PLUGS), shielded, and contains a trace antenna.
The Wi-Fi module with its shield removed
The switching relay
In order to switch the AC voltage, a relay is used. The relay used is manufactured by Shori, part number S3H-5-1A.
The relay is rated for 15 amps at 125VAC. The relay has a coil of 5V and draws 72mA. The output pins of the Wi-Fi module can not drive the relay coil directly— therefore, a transistor (Q2) located on the bottom of the AC board buffers the signal from the Wi-Fi module.
Due to the inductive nature of the relay coil, a flyback diode (D7) is used.
The diode and transistor
Wrapping it Up!
The parts of the IoT outlet
Today IoT devices are very popular and this popularity is only expected to increase from here. The design architecture of these devices is not new: A relay control by a transceiver module has been around for decades. Rather, the key component for these IoT devices is the software and platform integrations they contain.
Thanks for taking a look at this Teardown Tuesday. Stop by next week for another teardown!
Next Teardown: TV Remotes
More uses of gates
The current carrying capacity of a PC Board is determined by how thick and wide the conductors are, not the “thermal mass”. Standard PCB copper is what is known as ‘1-oz’ copper. 2-oz is available. As might be expected, 2-oz copper is twice the thickness of 1-oz copper. This makes the resistance of 2-oz copper 1/2 the resistance of 1-oz copper. The current carrying capacity also goes up by a factor of 2 (for the same temperature rise).
Because 2-oz copper is usually special order and costs more, the same equivalent can be achieved by adding a layer of solder to 1-oz copper. If you really need to increase the current capacity of a PC Board, specify 2-oz copper with 2-oz solder coating (definately special order). I once designed a PC Board that was required to operate at 75 amps RMS at 600 volts. The system operated up to 25 kHz so skin effect had to be taken into account. The traces were 1-1/2” wide, 2-sided, 2-oz solder over 2-oz copper.
“In an effort to increase the current carrying ability of the main power traces, solder is applied to the traces. The layer of solder over the copper trace increases its thermal mass. By increasing the thermal mass, the traces heat up less and hot spots on the traces are reduced. “
Rather misses the point and focusses quite bizarrely on a side effect. The resistance of a conductor (and therefore its current capability) is directly proportional to its crossectional area, basic stuff.