As a company we have expertise in designing Raspberry Pi extension boards, known as HATs (Hardware Attached on Top). The HAT we have designed for the Warm Church project is quite a simple one but we have added several facilities to it that we felt might be useful.

• Two relays. Although it is likely that you will only need a single relay (switch) to turn your heating on or off, we provide two, just in case. Each is capable of switching 5A at 240V, in other words 1250 watts of resistive load.
• A real time clock. The Raspberry Pi doesn’t have a real time clock, in other words it doesn’t know the time and date. Most Raspberry Pi’s are internet connected and query a time server to set their internal clock shortly after booting. If there is no internet connection then it doesn’t know the real time and date and this would make it difficult to control the heating. We include a real time clock with a battery back up that holds the time and which the Raspberry Pi reads as it reboots.
• A 1-wire controller. This is a piece of hardware that can be used to communicate with wired in temperature and humidity controllers. Normally we would expect you to use wireless sensors for reading the temperature in the body of your church but it may be useful to check that your central heating boiler is actually working, by measuring the temperature of the hot water pipes. Warm Church can do this and warn you if the boiler isn’t working.
• Two LED outputs. We expect to use these to indicate if heat is being called for from each of the relays.

There, doesn’t it look pretty? This is a development version with only one relay in place.