Anth's Computer Cave

Mini home-automation satellite

The latest prototype hardware for the AAIMI Project is a smaller, less-intrusive home-automation satellite.

A compact home-automation satellite with light, temperature and movement sensors. Picture: Anthony Hartup

For those new to The AAIMI Project our satellites feature a light-sensor, temp-sensor and movement-sensor and they enable the AAIMI Home Automation system to control your home.

We've built a few prototype satellites so far and they are all working real-time with my current system. The only issue I have with the current satellites is their size.

For a while I have been craving a compact satellite that plugs directly into the wall socket. Because I'm trying to build most of these initial prototypes from salvaged parts I've been waiting for the right piece of junk to provide those parts.

Picture: Anthony Hartup

I found this old power-timer in a box of junk, and it was just the size and profile I wanted for a prototype home-automation satellite. As an added bonus it already had all the components to deal with mains power.

After removing a couple of screws and prying gently around the seam with a screw-driver the unit came apart easily.

An old 240V power-timer. Picture: Anthony Hartup

Inside was a gear assembly and what looks like a tiny AC motor that runs the timing.

The components from inside the timer. Picture: Anthony Hartup

First we cut some of the old standoffs and ribs away from the enclosure to free some space

Picture: Anthony Hartup

We also made two cutouts in the side for cables.

I dropped a relay and a PCB offcut into the empty enclosure and found there was ample room to work.

The relay and PCB sitting inside the enclosure. Picture: Anthony Hartup

We were now ready for the components.

The components for the mini-satellite. Picture: Anthony Hartup

We have a PIR movement sensor, a 5V relay and one of our trusty AAIMI light/temperature sensor boards.

We routed the 5V power cable to the sensor board and the relay power also feeds off that.

The relay power connected to the main PCB panel. Picture: Anthony Hartup

We then soldered the sensor-return cables for light and temperature, and connected the relay-signal wire.

The finished components packed into the enclosure. Picture: Anthony Hartup

You can see the components crammed into the enclosure. There was no room to spare.

The two cables that connect the satellite to the base-station are either end of a ten-metre RJ12 phone cable cut in half. They provide eight wires, of which I require just six. They also feature the rubber end pieces that fit perfectly into the slots we cut earlier.

This cable gives me five-metres travel from the base-station.

We fixed the components to the casing with super-glue and connected the movement sensor

With the internals finished, we now cut a hole in the front cover to allow for protruding sensors,

The top of the satellite enclosure. Picture: Anthony Hartup

We replaced the original screws then, to ensure everything was secure, we super-glued various joins around the enclosure.

We then connected the satellite to the latest AAIMI base-station(more on the third prototype base-station soon).

A compact home-automation satellite with light, temperature and movement sensors. Picture: Anthony Hartup

I have used this for a couple of days in my Nightly system and it works well, but there are a couple of concerns.

Firstly, because this satellite plugs directly into the wall socket, you need a wall socket with clear line-off-site to the area the satellite monitors. It's funny to me because I've wanted to build a direct-plug satellite for a while, but it was only when I built one that I realized I had no suitable power outlets in the rooms I wanted to use it!"

This is no big deal because I can still plug the satellite into an extension lead and place it where I need it.

The second concern is the retail relay board I have used.

Up till now I have used relays salvage from televisions to switch 240V power via the satellites. In the early prototype relays I included a status LED for trouble-shooting purposes, but now the design is stable, I no longer include the LED.

The cheap retail relay assemblies like the relay in this satellite have two LEDs, and at least one of them is always on.

With the current design, I suspect those LEDs can influence the light-sensor in the satellite. I can use something to sheild the light-sensor from the LED, but it is not just the light readings I worry about.

What if the LEDs and the circuitry that powers them are also emitting heat?

Sure, the home-made temp-sensors we are using are not exactly lab-grade equipment, but with careful calibration they are quite accurate, and they are only about 10mm from the LEDs and their power regulators.

When I do the final calibration on this temperature sensor I'll compare the data to the others.

To be continued....



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Next: Wireless satellite



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