SKT Smart Home: making of a motion sensor

Small lifting electromagnet

SK Telecom's Smart Home device line-up was conspicuously missing a motion sensor. It would have nicely complemented the Jikimi home security devices. Considering that the PIR (passive infrared) sensor itself doesn't cost all that much (some as low as US$2) or complicated to work with, it wouldn't have been so hard to create a product out of it.

It turned out that SKT wanted that as a part of a much more beefed up home security solution called "T View Sense" that came out last month. It's a cloud-connected IP camera with the optional sensor package (motion, door, temperature/humidity, smoke, and carbon monoxide). The sensors requires the IP camera to function because they communicate to the server via the camera's integrated gateway. I appreciate the effort SKT is finally making to counter the IP camera efforts from the other mobile carriers (LGU+ had theirs since 2013), but the pricy nature of the camera (official price of KRW159,000 or about US$140) is off-putting to someone who's just interested the sensor alone.

So I decided to be a bit creative and repurpose one of the existing Jikimi devices into a motion sensor instead. Initially, I wanted to modify the SOS button because it was cheaper. But the fact that the alarm it makes doesn't get differentiated between the buttons made it a deal-breaker. With the door sensor, I needed to simulate the door closing/opening with a magnet, meaning that I could either attach the included magnet to a motor or use an electromagnet to fake such action.

Getting the door sensor to sense the electromagnet

Obviously, I chose the electromagnet because it would be far more simpler if it worked. If it generated enough magnetic field, it would act like the original magnet and cause the sensor to send a "door closed" signal. The problem was that I wasn't sure what kind or how big of an electromagnet would be necessary. After looking at various offerings on the internet, I decided to take a stab in the dark and buy a small "lifting electromagnet" used in machines for picking up metallic items. The particular model I bought for about US$5 was rated for 2.5kg at 12V DC, consuming 3W. The model number KK-P20/15 apparently indicates a 20mm outer diameter and 15mm thickness.

12V was tad higher than what I wanted, but the electromagnet works at a lower voltage with reduced pulling power. All I needed to know was whether that pull is just enough to trick the sensor, so I created a quick testing platform with my kids' electric circuit kit. As you can see here, 3V was just barely good enough for the sensor to activate. At 6V, it worked more reliably. This confirmed two things - the electromagnet I had was fit for the job and that I could make it work with a battery pack, e.g. single-cell Li-Ion battery (3.7V nominal).
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SKT Smart Home: Jikimi SOS button & door sensor

SKT Jikimi - SOS button (left) and door sensor (right)

On December 12, 2016, SK Telecom expanded its Smart Home suite by releasing a device set called Jikimi ("Protector") for basic home security. It consists of an SOS button that can notify either the police or someone you know, and a door sensor that can detect intrusion. They can be bought separately, and while the list price is KRW35,000 (US$30.70) for the button and KRW45,000 (US$39.50) for the sensor, it's currently being sold at a significant discount - KRW22,500 (US$19.70) and KRW24,000 (US$21), respectively. As far as networked sensors go, the discounted price is reasonable. I managed to buy a few of these shortly after they became available to gauge their usefulness.

Contents of the package - manuals (left), security stickers (center), SOS button (top right), door sensor (bottom right)

Both devices come in an identically sized box roughly the size of a hockey puck. An instruction manual and two security stickers are included with each device. The stickers are meant to warn off would-be intruders. While I doubt they would be much of a deterrent, the large one refers to an actual NSOK security dispatch service for the SOS button which you can optionally enroll for an extra KRW40,000(US$35) per year. It's not available for door sensor users, but this sticker is included with that device as well.
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SKT Smart Home: Smart Button Kkuk

Several boxes of Smart Button Kkuk ordered online

SK Telecom, the biggest mobile carrier in Korea, is the parent company of SK Planet, which owns Korea's 2nd largest online shopping mall, 11st (11๋ฒˆ๊ฐ€, 11th Street). So it was natural to see that SKT would come up with a clone of Amazon Dash, which simplifies online ordering with the push of a physical button. It's called "Smart Button Kkuk(์Šค๋งˆํŠธ ๋ฒ„ํŠผ ๊พน)", and became available in September 19, 2016, about 18 months after Amazon Dash's announcement.

Initially affiliated with about 60 items in 11st and given away for free with first 50,000 orders of the website's "Now Delivery(NOW๋ฐฐ์†ก)" service (this itself is 11st's version of "Fulfilled by Amazon"), it's now able to order from more than 140 items and shipped for KRW100 (US$0.09) when ordering certain specially marked items through Now Delivery. As of this writing, the stock of these buttons have apparently run out, but I expect it to be replenished soon.

Contents of the box - instruction manuals and the button

As with other SKT Smart Home devices, the button comes in a brown box with standardized instruction manual included. Looking at the device, the red button with 11st's logo on the left side is what you use to both pair and eventually order items online. The body is elongated to the right to house the battery. Like Amazon Dash, a removable hook is provided so that it can be hung.
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SKT Smart Home: Tale of two smart plugs (Witty & Dawon)

Smart Plug "Witty E" WIP-02A, unboxed

Lots of companies are hopping on the wave of Internet of Things (IoT) these days, each trying to build an ecosystem of their own. Major Korean mobile carriers (SK Telecom(SKT), KT, and LGU+) are no different, each setting up proprietary efforts. I used to largely ignore them because they required monthly fee, ranging from a few dollars per device to tens of dollars for "unlimited" (discounted with multi-year contract). With many non-carrier solutions usable without fees, I felt this to be undesirable.

However, SKT must have felt that this arrangement was hurting their chances for wide acceptance, because it began offering some of their affiliated products free of monthly fees, charging only a nominal (KRW 5,500, US$4.80) one-time fee included in the sales price since last October. I decided to take the bait and started integrating their home IoT products, sold under the "SKT Smart Home" brand, into my house. The very first one was a smart plug. The one you see here is the one made by Witty.

Smart Plug "Dawon Power Manager" PM-B400-W2

Over time, I installed several of these plugs around the house and some of them came from another company, Dawon DNS. Because SKT was selling them, lots of things were made to be nearly identical, namely the packaging and the functionality. The frugal-looking brown paper boxes contain the plug and the instruction manuals, all of which look almost exactly the same except for the diagram of the plug. Both companies' plugs are controlled by the one and the same official app, and works largely like as if they are the same product.

Even the price is similar, at around $22.50 to $26, which makes them one of the most inexpensive options. This includes the aforementioned fee, so the pricing is rather aggressive. The deal is made even sweeter by the fact that the plugs do not need any gateways or hubs to operate as some other solutions do (namely that of other carriers'). It will interface directly via Wi-Fi, so if you already have a wireless router at home there's no additional cost involved.
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Apple Watch 1st gen vs. Series 2 - Battery

I was quite surprised to see my Apple Watch Series 2 having more than 60% of battery on the first day of use. To see that this was not a fluke, I kept checking for a few more days and realized that it usually had 50% or more left after 24 hours with light use. In such cases, I was able to go without recharging for two full days. This is quite a bit longer than the Apple Watch Gen 1 even compared to its early days. So to make this clear, I did a comparative battery discharging test to produce the graph below. The devices had watchOS 3.0 installed at the time.

Apple Watch Battery Discharge Graph
Apple Watch Gen 1 lasted 24 hours 45 minutes, while Series 2 worked for 38 hour 50 minutes, about 57% longer. For Series 2, it still effectively meant two days' use - have it fully charged on the morning of day 1 and it will last until late evening on day 2. You can also see that if there was less activity, 48-hour use would have been possible as well. What's more interesting is how much battery is consumed for certain activities.

Activity Drain (%/hour)
Gen 1 Series 2
App Use 18.0 9.4
Exercise 18.0 8.3
Office (Day 1) 3.1 2.8
Office (Day 2) - 2.0
Sleep 1.9 1.1

During regular office work, the drain rate is similar for both watches. But once they're subject to more demanding tasks like logging an exercise or actively running apps, Gen 1 tends to drain about twice as fast. The idle state shown by the sleeping time is also less efficient compared to Series 2.

Early parts leak showed that Apple Watch Series 2 42mm models have about 36% larger battery compared to Gen 1 (334mAh, from 246mAh). So the difference isn't just coming from a larger battery, but an even more energy-efficient system overall. Considering that Series 2 has a CPU twice as fast and a screen twice as bright, this is quite a feat.

Now, it's been suggested that Apple put a larger battery on Series 2 because it includes a GPS module. This would enable path logging without a paired iPhone at an expense of a faster battery drain. So let's see how much difference it makes.
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Copyright (C) 1996-2016 Wesley Woo-Duk Hwang-Chung. All rights reserved.