Home Automation


Overview Hardware Software Applications







NOTE: Since getting the HV-Pro I use the onboard relays instead of two relays in a project box. The operation is still the same, just without external relays.

This is really simple, and it works beautifully. Inside the box are two relays. One is normally open and one is normally closed [they're actually two identical relays, but I use the N.O. contacts on one and the N.C. contacts on the other] and they're connected to the thermostat on the first floor. The thermostat is a basic mechanical model and has one pair of wires going to the boiler. When the wires are shorted the boiler comes on. 

The N.O. relay connects across these wires and when HV energizes it the boiler comes on regardless of the status of the thermostat. The N.C. relay has been placed in-line with one of the wires. When it opens, and breaks any potential circuit, the thermostat can no longer call for heat. So HV has two possible operations: Interrupt Heat, and Demand Heat.

Even though we have a two family house there is only one boiler and there are no zones. To compound this problem the thermostat is on the first floor which tends to warm up before the second floor. My solution was to run a piece of CAT5 to the second floor and stick a project box on the end. This box has a DS18S20 temperature sensor in it. So I can have a minimum temperature set for that floor and HV can override the thermostat if it needs to.

HV also interrupts the heat when it isn't needed. In our case, "isn't needed" is defined as either: "nobody is home," or "everyone is asleep." Because we arm our alarms in stay mode when we go to bed all HV needs to do is monitor the status of the alarm to determine when to cut out the heat. If both partitions are armed [in either away or stay mode] HV opens the N.C. relay. And in the morning, a half hour before we wake up [6:00am on weekdays] HV closes the N.O. relay and the house is nice a toasty for us when we step out of the showers.

The box housing the relays and LEDs.

HV thermostat control schematic.



Cooling the house is handled by a single 15,100 BTU/hr wall mounted A/C. Each floor is only 720 sq. ft. so this is more than adequate for the first floor, and even spills into the ground floor to make it bearable. One of the keys features that led me to choose this unit is that it comes with an IR remote. So I taught HV the IR signals and it can now control the A/C. But the problem is knowing the status. Is the A/C on or off? Because the remote control uses a toggle for on/off, HV needs to know the status before it decides whether or not to send the IR command. At first I tried using a home built air flow sensor. I tried two designs that consisted of a flap that would close a circuit when its position changed because of the moving air. These would work for a couple of days, then something would come out of alignment and they wouldn't close the circuit anymore. I probably could have come up with a better design if I had used a mercury switch, but I decided to go another route.

I bought a split-core current transformer with the idea that I'd measure the current being drawn by the A/C. Now I would be able to tell the on/off state of the A/C and the on/off state of the compressor [and maybe, if the resolution was fine enough, the hi/med/lo state of the fan]. So the transformer is placed around one of the conductors of the A/C's power cord, and it's output goes to a project box which contains a simple circuit to convert the 0-12VAC output to 0-4VDC for one of HV's analog input ports.


HV A/C control and feedback.


The circuitry to detect the A/C state.

The box containing the A/C status circuitry.