Why?

Over the summer I moved into my own flat. As the weather starts to get colder I’ve found myself thinking that the heating might need switched on once in a while. I don’t need to heat my flat if I’m not around, as long as it’s not so cold the pipes freeze! I’m generally out doing something most weekday evenings and I’m not sure in advance when I’ll be back. I would like to control the heating remotely so i can switch it on when I’m 20 minutes from my flat, just like they showed on Tommorows World in the 1970s.

I’m sure there is a handful of startups pushing their answer to home automation to save the world from climate change. You buy a starter pack including monitoring nodes  featuring exclusive patented SenseMeNow™ technology and a one year subscription to their cloud based monitoring service. Don’t get me wrong I’m not having a go at these solutions, they are the best thing for 99.9% of the population, but I would much rather get my hands dirty, and learn stuff in the process…..

The central heating boiler is at the back of my flat, quiet a bit a away from my living room and ADSL router etc. There is a Wi-Fi signal but it’s a little weak, however the telephone Master socket isn’t too far away from the boiler, that gave me idea.

Rewind 20 years…

When I was a child, I would be round at a friends. When it was time for me to go home I would ask to use my friends parents landline (mobile phones were things installed in the central console of traveling salesmans’ cars) so I could let my Mum know I was on my way home. Rather than waiting for the phone to be answered and having a brief conversation, resulting in a call charge, a code was agreed. If I let the phone to ring 3 times before hanging up it meant I was on my way home, there were also other messages that could be passed on, I forget the details

Fast Forward to 2012….

So I needed to come up with a signaling method that could be used to switch on the heating but wouldn’t be falsely triggered by normal phone calls. I decided on a three sets of rings in 90 second period.

Ring Sensing

With the telephone ring signaling technology remaining essentially unchanged for the last 100 years it is something that can be sensed with a simple circuit. I was able to get reliable results without using zener diodes, just one silicon diode.

Microcontroller

For prototyping I’m using an Ardunio Uno, with the plan to shrink this to an ATTiny85 once I had got the circuit worked out and tested.

Boiler Interface

Warning
You are responsible for ensuring that you are aware of the hazards and precautions when working in the proximity of 230V AC (isolate power before opening any covers etc). I did all this work without breaking any “gas seals”.

I was fortunate in that the previous owners of the flat has left the manual for the boiler (Modena 102) that included a electrical block diagram.

For whatever reason the boiler installer hadn’t fitted a room thermostat so I could simply put a relay where a room thermostat would have been wired.

Connection made to the terminals circled in red

“Thermostat” Connection, orange wires go to relay connected to Ardunio

As the voltage being switched is 24V AC I don’t need to take the precautions that would be required for mains voltage. In the case of boilers that use 230V for the room thermostat a relay can still be used but it must be rated for 230V and separation maintained from low voltage circuits.

Automated Dialing

Rather than manually dialing and hanging up I’ve created a Tasker task that automates the process on my android phone.

So without futher delay here it is in action

Drawbacks

Anytime I switch the heating on my phone rings multiple times. If this happens to be at 2am after a late night hacking session this may wake my neighbors. I don’t want to switch my phone ringer off as I want to know if somebody is phoning me 🙂

Improvements

After getting the phone controlled version working I’ve decided that being able to control via the Internet would be useful. The addition of extra features like temperature feedback would also be much easier. At last a useful application for the Nanode that has been gathering dust for the last year. More about that later….