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Home Control – The Full Mesh

Danger sign - Peter ScargillI’ve been working on home control now for many years on and off both professionally and today as a hobby (for now). This blog documents the latest state of play.

My first attempt at home control years ago took the form of a bunch of boards talking to each other around a building by cheap telephone cable. Simple as that may be it can be a deal-breaker when it comes to wives who don’t like wires! Today this needs to be handled as far as possible, wirelessly.

Home Control App - Peter ScargillTalking to a home controller via mobile phone is a no-brainer – simply fit Ethernet capability to an microprocessor board and there are solutions out there for talking to mobile phones, one which takes some work but which yields one of the best visual interfaces to date is NETIO. I’ve developed my own Android software and that works well, but for now, visually, NETIO remains my tool of choice – though lack of updates from the designers is starting to grind a little – such is the way of Apps.

To get instructions delivered around the building, for the last year I have been struggling with a low-cost radio called the NRF24L01 – these are readily available on Ebay and are small and cheap – however they do not suffer stone walls gladly and have somewhat restrictive range, due mainly to their choice of operating frequency – 2.4Ghz which just happens to be the same range as everything from WIFI routers to cordless phones and more. Their advantage – cheap.

Within that restriction they are quite reliable – I’ve sent hundreds of thousands of data packages in a row without error. In order to get past the stone wall issue, it’s no good having a controller simply talking to radio units (which is how you avoid wires all over the house), you need some kind of network so that units can pass message from one to another. Because the Atmel Atmega328 processors I use (custom variations on the basic “Arduino” theme) are limited in capacity, as is the NRF24L01 radio, up to now it has been impossible to to manage anything more than a limited form of hopping network where certain “nodes” or slave units act not only independently but also as “relay” nodes, passing messages on to others and hence increasing the range of the system.

Full MESH Home ControlWhat has always been needed was some kind of full mesh where all units can act as gateways to others and where the failure of one unit results in the mesh re-adjusting itself automatically to handle that. Up to now that’s been a dream but the software now exists to do this – called RadioMesh.  The nearest anyone has come up with until now was RF24NETWORK, a simple network but not a mesh – in this network up to 6 units could each talk to 6 others and so on – the limitations included the need to specify exactly who would talk to who – so if one unit went down it could bring the whole network down. Accordingly I’ve been spending my evenings and weekends gutting my software to try to accommodate some new software which forms a “mesh”… and the work has paid off – I now have a rig up and running.

Mesh Radio Home Control - Peter ScargillAs you can see from the above, I’ve used the Atmel 1284p for the “master” unit – I long since gave up on the 328s for this – just not enough RAM or storage memory  – and I’m now about 2/3rds through the 128K memory that comes with the 1284.  On the other hand, “slave” boards which have no Ethernet can JUST about handle a range of functions and the mesh at the same time.

Each “slave” board has an output to control serial LED strip (which needs a separate 5v supply), 1 Infrared output, 3 normal digital outputs, 3 PWM outputs (again handy for LEDS), 2 general purpose analog (or digital) inputs and 2 temperature sensors. I’ve also incorporated an inexpensive 433Mhz transmitter to replace wireless remote controls – but that’s not 100% yet. The main board has an Ethernet Connection and also an optional output to an LCD display – the slaves also have similar outputs to an LCD display and in each case I made the decision to give the display it’s own intelligence – i.e. it’s own processor – so that I end up using the serial out on the slave boards and the SECOND serial out on the master for this purpose – hence the displays are optional without any software changes.

PC-Based Controller Tester - Peter ScargillThe master board is able to update Google Docs spreadsheets, send emails and Tweet – I’m currently still experimenting with the above as the email tools have a tendency to take too long to operate (but still work).

If you look up “Scargill home control” on Google you’ll find a host of earlier articles including some in-depth stuff and on YouTube I’ve detailed my experiences with the NRF24L01 radio units. Amazingly this has had well over 20,000 views! https://www.youtube.com/watch?v=VgmVYdSCNLs

Next steps – I’m working with a pal and we’re going to take a look at Atmel’s own mesh software for a chip they do with radio built in – we’ve a very tiny PCB on the way from China to test this out  – also I’m pondering putting the radio part on it’s own 328 chip with a slave SPI interface in order to allow it to concentrate on radio reliability while taking a whole load away from the main board. It sounds over the top but given the very low potential cost of a 328 chip and crystal, such a solution would leave more memory and MUCH more program space in the main board for improvements and new features. Watch this space.

This all sprang up from my original article on a cottage thermostat in which I envisaged a very simple controller. Then came the UberBareBoard article about an Atmega328-based Arduino clone, initial attempts to master the NRF24L01 radio. The next article was the first item entitled home control and after this – then part 2 and then the winter update – then the April 2014 update and then things really started to move as I discovered better networks – and better radios in the the September update where I discovered Radiohead, the Si4332 and RF22 radios.

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