Wesley's Tool-Box

Apple HomeKit platform goes back to iOS 8. It was not very fleshed out at the time, needing more polishing over the years. Last notable change to HomeKit was made in 10.2, which enabled device notifications. This, along with other improvements in iOS 10, led me to think that HomeKit was finally in a "usable" state. Thus I have invested in the HomeKit ecosystem since early April of this year, around when iOS 10.3.1 came out.

As I gathered enough tangible material to share, I did a 5-part write-up of my HomeKit experience, spanning sensors, lighting, and energy control. I felt that my 5-month experience in a non-American environment may be of use to many people who are considering the platform.

1. Moving to Apple HomeKit with Elgato Eve
2. Philips Hue adds light to the HomeKit setup
3. Controlling 220V Power & Light with HomeKit
4. How much power does HomeKit use?
5. On installing and configuring HomeKit lighting

But now, big changes are coming in the coming weeks. Most notably, the GM(Golden Master, finished version) of iOS 11 will come out in two weeks, as Apple's new iPhone announcement will be made on September 12, 2017. It will contain significant improvements for HomeKit. As noted in the 5th post, Philips will expand the range of Hue products that will be recognized in HomeKit. Elgato has announced five new HomeKit products including lock and smoke detector.

All this means that my iOS 10-based HomeKit write-up should be wrapped up at this point. I'll come back to this topic as the dust settles and I had my hands on the new features and products.

There are some things to consider and take action when you're installing smart lighting, HomeKit enabled or not, around the house. For the light switches, the biggest concern is the presence of a neutral wire. In most cases, you need this for a smart switch to function, but many switch boxes omit this and make things complicated. To see why things are like this, we need to take a look at the circuit diagram.

For a light to turn on, it has to connect to both ends of a power source. This is generally a single-phase AC power, which can be derived from a 3-phase AC power by using one of the phase wire and a neutral point. The wire connecting to the neutral point becomes the "neutral (N)" and the phase wire, the "live (L)" as seen in the diagram.

With a regular switch, all you need to do is to connect or break the connection between the live wire and the "load" wire leading up to the lamp. Therefore, a switch box only needs to have the live wire and one or more load wires coming out of it. Number of load wires correspond to the number of controllable light fixtures, of course. Neutral wire could also be present, but it wouldn't be connected to anything because there is no need to.


The situation becomes different with a smart light switch. In order for the control module in the device to work, it also needs to connect to both ends of a power source, but at all times and independent of the lighting. As the live wire is already present, we need to add the neutral wire to the device as seen in the circuit diagram. With this configuration, the switch connected to the live wire and the load wire could be controlled either manually or by the control module. This is the reason why most smart light switches require the neutral wire.

The rare exceptions that can forgo the neutral wire have the control module connect between the live and the load wires. The module itself consumes little power and a very low current leaks through the load wire in the "off mode" so as to effectively prevent the lighting from turning on. But this generally requires the lighting load to be sufficiently large. If not, the leaked current may cause the lighting to flicker or cause other problems. In other words, this solution isn't as widely compatible as the switches using a neutral wire.

Months into using the SKT Smart Home as the home IoT system, several shortfalls such as the lack of interaction beyond the main app and no actual user-side ownership of data left me feeling unfulfilled. Meanwhile, Apple's own home IoT efforts, HomeKit, had been maturing and being quite an Apple enthusiast, I thought this may be a good time to give it a try.

First appeared on iOS 8 in 2014, HomeKit finally got its own system app "Home" and a place in the Control Center with iOS 10, along with notification from accessories (iOS 10.2) and geofencing support. With the upcoming iOS 11, it's set to become even more powerful, supporting more accessory types, per-user geofencing, better timing options (offsets and delays), shorter Bluetooth LE latency, and hobbyist development of accessories.


For my first HomeKit accessories, I picked up several types of Elgato Eve sensors during my Fukuoka visits in April. Eve Weather tracks the outside temperature, humidity, and air pressure. Eve Motion senses human movement up to 9 meters in the 120 degrees' field of view. Eve Door & Window detects the opening and closing of openable items. They seemed to be good starting points for future expansion because they provide sensor data that can trigger actions.

Now, the reason why I bought them in Japan is because most of the HomeKit-enabled accessories are not sold in Korea at the moment. They are most prominently available in the U.S., but this means that anything that runs off AC power like power plugs and light switches are often 120V-only, incompatible with the 220V outlets. Battery-powered ones can be found with relative ease in many Eurasian countries. For now, I'm sourcing various accessories from the U.S., Germany, and Japan.

FYI, the sensor series for Elgato Eve are most widely available around the world and you should compare the prices when buying them from overseas. Price in Japan isn't particularly favourable, so you should pick them up from physical stores only if you're already visiting the country for other reasons.


Eve sensors are battery operated, so they can be installed freely around the house. What's more, batteries in these sensors last at least a year according to Elgato, so they need little maintenance. More than two months into their use, battery indicators have barely budged. Should the batteries eventually run out, Eve Weather and Eve Motion use standard AA batteries, so they are cheap and easy to replace.

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.


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).

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.


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.

Last year, iPhone 5S came with a motion co-processor called M7 that can collect various sensor data relating to iPhone's motion. The most notable use for this was recording how many steps a user took while carrying the device. In other words, the device acted as a pedometer. This year, iPhone 6 series has updated the co-processor to M8 and added another sensor - a barometer. The Health app that comes with iOS 8 makes an immediate use of this. It records how many floors the user has climbed, adding another dimension of knowledge to the user's movement.


Apps that are updated to use the Healthkit in iOS 8, such as Argus, can read this stair climbing data. The notification widget from Argus is able to display the number of floors I moved up during the day if I'm using an iPhone 6 Plus. If I'm using an iPhone 5S, there's no such data available, so the widget simply doesn't mention it at all.

While I'm comparing the data from both devices, I should note is that the pedometer function acted very similarly between each other. However, as you can see in the pictures, iPhone 5S consistently recorded a bit more steps than iPhone 6 Plus, for some reason. Perhaps the bigger form factor and weight of the 6 Plus dampened the recorded movement a bit.