Enhance the intelligence and safety of home energy monitoring with new electronic switches

Would you like to pay an additional $10 for some valuable information to improve the quality of your home's power supply? For example, the actual power consumption information for refrigerators, dehumidifiers and air conditioners? My answer is "maybe".

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Whether or not to invest in power detection technology depends on many factors. What I immediately thought was: Is the installation simple? When can I access this information? Is it reliable? Is the data accurate? Is the data measurement information sufficient for me to make a correct conclusion? Can it be used?

Next, we spend a few minutes to understand some background.

Home monitoring ensures safety and peace of mind

When I was not living in a lakeside villa, I made a low-tech component that was used as an anti-theft measure to turn the TV and lights on or off at different times in the evening. I am using a mechanical timer of $12 as shown in Figure 1. This infrastructure has obvious limitations. I don't get any feedback on whether the work is working or not, and I don't get any information about the switch signal. It doesn't take long for the thief to know that there is actually no one in the room, especially when a light bulb is broken. I will explain below why I would like to know about electrical signals. Fortunately, there is now a great solution to some of the drawbacks of mechanical timers.

Figure 1. Typical mechanical timer.

Belkin's WeMo Switch wall switch (Figure 2) is a modern way to provide varying on/off times, especially when combined with its motion sensor. Belkin's WeMo Switch and its accompanying app use the Wi-Fi network at home to enable me to control from a smartphone, tablet or computer. Initially, the price of $49.99 made me feel a bit expensive, but we can do a little analysis later.

Figure 2. Belkin WeMo Switch wall socket. Control TV, lighting, stereo, heaters, fans, etc. wirelessly.

As a platform for building a home network, I don't have to pay any installation fees, and it's completely modular. Intuitive, easy to set up, and when connected to an existing Wi-Fi router, you can add one WeMo switch at a time. I can plug any device into the outlet and I can change it whenever I want. I customize the notification rules through the mobile device, as well as the timer on/off cycle. When no internet is available, the WeMo Switch is like a mechanical timer.

Now, I can do things that mechanical switches can't do; but, slow... actually I haven't bought them yet. Why? Because Belkin has another set of programs I prefer.

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Page 1: Home monitoring ensures safety and peace of mind

Page 2: Adding intelligence to home energy monitoring

Page 3: Integration is collaboration

Increase intelligence for home energy monitoring

I need more than just preventing thieves from entering the room. After all, with the right "smart" switch, you can fully access every electrical device in my home via the Internet. For example, I want to remotely know if there is a malfunction in the submersible pump, dehumidifier, freezer or refrigerator. If the basement is flooded, the facility is damaged, or a batch of food is spoiled, the damage is easily more than $200. What investment can help me reduce losses and avoid the inconvenience caused by electrical failure?

I need a wealth of useful information to help me understand more about the state of electrical appliances and their power supplies. Is the equipment damaged because the quality of the appliance is not good or because the power supply is abnormal? Is the power control in the permanent house better than another power company in the lakeside villa? In my home in New Hampshire, it takes about 3 times a year to exceed 8 times. Hours of power outage. During power failure, is the electrical equipment over-stressed when switching to the backup power supply? Are the electrical characteristics of certain critical electrical equipment, such as pumps, dehumidifiers, refrigerators, or freezers, changing with aging?

How much does it cost to get more data and let me make an informed decision about electrical connections, home appliances and usage patterns? Can I even predict a possible failure?

Belkin has a simple, practical solution that takes care of most of my ideas. With an additional $10, Belkin is able to add "insight" capabilities to its basic WeMo Switch. Its WeMo Insight Switch (Figure 3) has a miniature electric meter inside, which is even smaller than the previous generation. Great! For a poker-sized switch with a $10 meter built in, the tech madman will be ecstatic? This idea is awesome. The user interface (Figure 4) is very intuitive and triggers a lot of family discussions, because both my 10-year-old daughter and my old mother are very easy to understand and control.

Figure 3. With the Belkin WeMo Insight Switch, you can turn devices on, off, customize notifications, and change device status from anywhere in the world.

Figure 4. User interface screenshot of the tablet.

The WeMo Insight Switch is very innovative and uses chips designed for electrical energy measurement of electricity meters. The chip is Maxim's 78M6610+LMU energy measurement processor that supports measurements such as current, voltage, power and harmonic distortion. In addition, the chip is also extremely accurate. Although I can't access all the data through the WeMo app, I am very satisfied with the power measurement. Anyone who chooses to design such a device using the 78M6610+LMU can use the information provided by the 78M6610+LMU to enhance the device.

The 78M6610+LMU itself has an RC oscillator and two low baud rate optocouplers that transmit their data to Belkin's communications processor. In this application, low speed is actually a good thing. In general, the higher the baud rate in the design, the higher the optocoupler price; the higher the number of components, the higher the total bill of materials (BOM). The energy measurement technology in the 78M6610+LMU compresses these costs. The automatic reporting function of the 78M6610 can send accumulated data packets at regular intervals, reducing the number of optocouplers and speed requirements. The main processor can choose to receive each packet or simply monitor the packet of interest. Never lose information.

The accuracy and linearity of the meter metering technology of the 78M6610+LMU are also higher than Belkin's requirements for monitoring household appliances, but the designers are very clear about how to take advantage. The 78M6610+LMU enables Belkin to meet its design requirements without incurring any additional calibration costs.

Finally, one design consideration for such devices is power and space issues—keeping low power and size. Belkin can use a current transformer to minimize resistive losses, but that will never fit the small size of the switch. An alternative is to select a 2mΩ shunt resistor to sense the current without interfering with accuracy over the entire current range; this method is effective, but consumes 10 times more power than, for example, a 200μΩ shunt resistor scheme. The 78M6610+LMU has a very small footprint and is incredibly low power, making it the best solution to this difficulty.

The 78M6610+LMU block diagram (Figure 5) shows that analog and digital technologies are integrated into the chip. The chip is grounded for reference and shares power with the communications processor.

Figure 5.78 The M6610+LMU box shows the integrated components: input multiplexer, 22-bit delta-sigma ADC, 24-bit RISC processor (clock 20MHz), RAM and non-volatile memory, and serial interface options. The chip also has a preamplifier gain stage, a temperature compensated reference, an RC oscillator, a temperature sensor, and multiple voltage fault comparators not shown.