Anth's Computer Cave

New AAIMI Home Automation base-station

Today I'll share the build for the new AAIMI Home Automation base-station.

The main AAIMI Home base-station. Picture: Anthony Hartup
The rear view of the base station

The old base-station was working fine, but it was running out of room. There was no space left for cabling to run extra satellites, and even simple maintenance tasks were difficult with all that wiring in such a small unit.


I wanted to use salvaged parts, as usual, and this time I settled on the outer casing from a VCR unit.

The salvaged VCR unit. Picture: Anthony Hartup
The salvaged VCR in its original form.

This has ample room for expansion, yet it fits easily into a TV cabinet, which is where the system is designed to live.

I had hoped these VCRs would have their own dedicated power supply (PSU), but that was built into the main control board, which had to go.

Instead I am using a 12V PSU from a PlayStation2. It pushes 7 Amps across two rails.

A salvaged Sony PSU. Picture: Anthony Hartup
A sony PSU and switch.

It also has a nifty plug and switch.

To convert the 12V to 5V for the sensors I built a dual regulator with a pair of 7805ct serial regulators. This will run light, temperature, movement and gas sensors now. Later they'll also power hall sensors for doors and windows, and pressure sensors for other security applications.

A 5V regulator. Picture: Anthony Hartup
A dual power regulation circuit using salvaged 7805ct serial regulators and capacitors.

To power the Raspberry Pi (which in turn powers the Arduino) I am using a 5V UBEC from one of my older robots. This is rated at three amps.

Picture:A 5V UBEC. Picture: Anthony Hartup
A 5V UBEC that may be more suitable for a helicopter.

Both these regulators are temporary. Serial regulators are inefficient and create heat, so I plan to swap them out for switching regulators in the near-future. I just used what I had for now and they are working.

Picture: Anthony Hartup
A relay-driver built from salvaged components.

This build users our older relay-drivers to activate the 12V relays. I have installed two dual units so I can power the relays for four satellites. Additional satellites will run from new wireless mini-stations, meaning I don't need any more than four connected to this main unit.

Picture: Anthony Hartup
The rear connectors for the base station.

The only thing I have actually bought for this build is is these spring-loaded plugs to attach the satellites. They make for easy connection compared to the small screw-terminals I used on the last unit.

They worked out at about 30 cents each in a bag of ten.

Putting it together

The first task was to reinforce the rear of the unit. It was mainly flimsy plastic with few structural ribs, and I needed to drill about 56 holes for connectors without cracking the plastic.

The method used to reinforce the casing. Picture: Anthony Hartup
A plastic section ready to laminate.

I cut some square sections of plastic from an old printer to fit between the ribs.

The reinforced casing. Picture: Anthony Hartup
The reinforced rear panel.

I attached these with contact adhesive to form a one-piece solid backing.

I was then able to safely drill the 56 holes through the unit without breaking anything.

Picture: Anthony Hartup
The panel with the larger holes already drilled.

To attach the various boards to the case I use pieces cut from masonry plugs, the ones you use to attach objects to brick and concrete.

A way to attach PCB boards to the casing. Picture: Anthony Hartup
A standoff cut from a masonry plug.

I screw these to the PCB boards then superglue the bottom of the standoffs to the plastic bottom of the case. Once dry you can unscrew the boards and the standoffs remain in place.

Case layout

Picture: Anthony Hartup
The chosen layout for the base station.

I have filled most of the floor of the case but there is tons of vertical space around the sides for extra PCBs and micro-controllers if required.

There will be more wiring (another sixteen wires) when I add the remaining two groups of satellite-connectors, but overall it is tidy enough.

Picture: Anthony Hartup
The rear-view of the partially-finished base.

The rear section is not quite finished.

I made a male-to-female Ethernet cable and glued the plug alongside the power switch. I still need to find a male-to female usb cable and HDMI cable and add the last two groups of spring-plugs. Then all the connectors are on the exterior, meaning I can permanently close the lid.

Each group of spring-plugs has identical pinouts to allow easy satellite connection.

Picture: Anthony Hartup
The standard pin configuration.

On the left, the 5V constant power runs all the sensors in each satellite, while the 12V pins come directly from the relay drivers in the base. The sensor return wires connect to the first three pins on the right, and the last pin is available for other analogue sensors. I am using one of these spare pins for a gas/smoke detector.

The CircuitDraw wiring diagram for the base station. Picture: Anthony Hartup
The complete wiring guide for three satellites. To see full-size image, right-click and select View image or Open image in new tab. Diagram created by Anthony Hartup.

The diagram above shows the wiring configuration to match the code in the upcoming AAIMI Home Automation 0.2 release.

So here is the (almost) finished base station.

Picture: Anthony Hartup
The base-station waiting patiently for a paint-job.

When I take the top off for the last time to add the other spring-plugs and USB/HDMI cables I will paint the whole thing black and it should look great.

I'll add the pics here when it's done



Previous: Panning security camera




Leave a comment on this article

Leave a comment on this article