We recently discovered another GSM controlled switch for remote control of your central heating. This is one of the most affordable units we’ve come across yet so we contacted the company and had them install a unit for us. Here’s how it works… .
The unit cost us £209 delivered and we used their installer that covers our area and it was fitted, up and running in around an hour. Installation cost £60.
The hardware includes 2 power relays outputs (5 amps max) and 4 input terminals. The relays are most common used for Central Heating and Hot Water circuits, but could be connected to gates, garage doors or any manner of other hardware. The inputs can be used to let the home owner know when their security system has been tripped or perhaps warn of a flood or freezing temperatures with the correct sensors. The GSM module is a quad-band (850/900/1800/1900 MHz) unit and the unit sips power at around 20mA in standby and 500mA when communicating.
Operation – Our installer programmed our unit but you can change the program yourself remotely (add or change mobile numbers etc) through a website. There are two modes of operation. With the first you can dial the unit to turn on your heating. A call from any recognised number (multiple numbers can be stored) will be rejected and the heating turned on and a timer started (from seconds to hours). This has the advantage of incurring no phone costs as the call is rejected rather than answered.
The second (and seemingly more popular) option is controlling the unit via SMS text message. Sending ‘Heating On’ turns on the unit and starts the timer. The advantage of SMS control is the resultant confirmation messages, in this case ‘heating on OK’. Texting ‘Heating off’ has the expected action and the confirmation text of ‘heating off OK’.
Sending a text message ‘Status’ to the unit will result in a reply showing the current state of each input (A,B,C and D) and each output (X and Y) plus the signal strength and voltage of the system (see iPhone image at the top of this article).
The unit came with a PAYG SIM card with £10 credit. For someone using the unit on a holiday home or caravan this could last a year or more but it’s worth pointing out many SIMs require a periodic top-up to stay working.
Conclusion – The SMS Central Heating system is a neat and affordable unit which works well. It has the hardware flexibility to expand into other roles too and with its dual modes of operation it’s ideal for a wide range of smart home applications.
- 2 output contacts of power relays X and Y (each allows up to 5A/250V)
- 4 input terminals A to D for SMS reporting (the inputs react to a connection or disconnection to or from a common GND terminal)
- A switch with SMS remote control. SMS texts for switching particular terminals on/off are configurable.
- A time-switch which can be activated remotely via a mobile phone (the switch-on period is configurable from 1 second to 10 hours).
- A relay with dialling-in remote control. Up to 50 tel. numbers can be authorised for each relay. Because calls are not answered dialling-in control within GSM is free of charge. (David only checks the caller’s number and – if the number is authorized – responds with relay activation.) This can be used for parking latch control etc.
- A relay with validity-limited dialling-in remote control. Each authorized number can have a limit to the number of calls. When the call count reaches the limit the tel. number is de-authorized. This can be useful for pre-paid services such as e.g. parking. Any tel. number can be re-authorized via SMS by the administrator.
- An SMS reporter. Input A to D activations or deactivations can be reported by SMS and optionally confirmed by phone calls. Each input can have its own message texts and up to 8 tel. numbers programmed.