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Archive for September, 2014

Home Control September 2014 Update

Streuth.. I’ve just realised I’ve been running this blog since 2005! Doesn’t time fly. My interest in using Atmel technology for home control started with an article I wrote back in 2012 simply called “Home Thermostat”. At that time I was just playing – but messing with prototypes really isn’t much fun so shortly thereafter I design the “UberBareBoard”. That article was followed up by my first attempt at home control over the Internet and part 2 by which time I was starting to see some real potential for not only my home but our holiday cottage business and for our place in Spain.  Then came more updates as I got to grips with the more powerful Atmega1284p chip and started to develop my own PC-based test tools. By July I had it all figured out – or so I thought – using RF24NETWORK software providing a mesh-type network of radios still using the NRF24L01 radio.

Amazing how things change. The NRF24L01 boards which – I’ll grant you are cheap, continue to function poorly –they do not like stone walls and the RF24NETWORK is not a true mesh – you have to specify every node in the mesh which makes replacing boards a lot of fun.. and it really cannot handle one of the boards going offline. Finally, no-one has yet made effective use of interrupts when using these radio boards in a network – which puts further limitations on what you can do – as you spend your time constantly polling the radio network.

Over the summer, my pal Aidan and I have been working hard – we now have a decent Atmega 1284-based board to work with – you’ll see it below. Late July I discovered the Radiohead library – the nearest our little processors have come to seeing a proper mesh network.. but that now pushes the 328 chips out of the window – as the library takes them near the limit of their available program memory and as for the tiny 2K of RAM – just not enough. For boards at the end of the chain, perhaps – and I have 3 working installations using these – but for the master board, the 328 is no longer an option.

In August while enjoying the sun, it hit me – the NRF24L01 chips don’t have the ability to know how strong the incoming radio signal is – so how the hell can a network possibly know which is the best unit to route the signal through – and that started me on the hunt for alternatives – which brings us neatly into this post.

If you’ve been following my blogs you’ll know about my on-going work on home control but firstly you’ll see the phrase “Arduino” bandied around. I use this merely for convenience as I use a lot of the Arduino libraries out there – but my boards are home-grown. I’m particularly fond of the Atmega1284p chip because, unlike the standard Arduinos you see our there, this has 4* the RAM – which means it’s less likely to run out. It also has 4* the FLASH memory – so just when Arduino sketches are running out of room, the 1284p is just getting started.

AiduinoI used to use hand-made boards and there are plenty of those lying around, but these days I’m using a design we put together called the “Aiduino” – so-called because my pal Aidan did the board layout. This particular design has stood the test of time and I use these on everything. It has space for both 3v3 and 5v regulators, the chip, the usual support components and that’s about it.

You’ll see a typical Aiduino above with edge connectors for all the port pins and an SPI connector near the middle. I don’t bother putting the programming interface on the board as the low-cost FDDI interfaces do that all for you – why waste valuable board space. I simply allocate a 6-way connector on the edge of the board for programming.

Armed with these boards, I have LCD display controllers (for wall mount displays), a master controller with Ethernet card and “slave” units to control lighting etc. All of these units talk to each other using NRF24L01 radios which are very cheap 2,4Ghz popular radio modules. There are two problems with these radios – firstly they are very low power and secondly they are on the same radio broadcast range as just about everything else including WIFI – and they DON’T like stone walls.

I’ve looked at the cheap FSK units as used in radio remotes – no-where near powerful enough.

Aidan and I are investigating some Atmel chips with on-board radio – these look promising but getting all of that running in the Arduino IDE and hence keeping access to the Arduino libraries – is proving a challenge but watch this space as he’s working on this right this minute. We’d like to produce (where others have failed) a tiny radio module which runs on SPI and which internally handles all the mesh coding and massive buffering – as well as offering other functions to take the load off the main boards.. Meanwhile…

tmpB859I’ve looked at the RF22 modules – but these come from the USA and hence are a little expensive (inc. postage).. but only in the last few weeks have I discovered even cheaper Si4332-based radio boards from China which are compatible with the RF22 modules and hence can work with the likes of the Radiohead library for Arduino – a simple but fully functional “mesh radio” library. Not only that but these radios and library combined, unlike the slightly less expensive (but only just) NRF24L01 units, make good use of interrupts to ensure you can actually do something else while the radios are working!!

See the radio on the right – that’s one of them. They are tiny which poses a problem for prototyping as the edge connector is 0.05” pitch – but it’s do-able with care.

Below you’ll see one of my bodged Aiduinos which has the radio board mounted on top of the 1284P chip. If this all pans out I’ll make a board that incorporates the radio… and in the process of research I’ve found out some interesting things about these little radios.

tmpCF15I can say that I’ve had 3 of these running in mesh mode and the range covered by 3 equally spaced units (the centre one acting merely as a message relay in this case) covers from my garage, to my greenhouse – through 4 stone walls and an intermediate lightweight wall – which is WAY better than the NRF24L01 chips can manage.

At first I managing a couple of message round trips a second – I needed to get the speed up to dozens of round trips a second in order to allow me to, for example round-robin poll several units to update the mobile phone.

Well that worked too thanks to some help from the designer of the Radiohead library – a change from the library defaults brought me to 100 package round trips a second – when I say package – we’re talking about, say a 20 byte package going there and back – and with additional maintenance bytes (from, to, ID etc.)

The chip used in these radios, the Si4332 is supposed to handle a maximum +20db output  – I managed +17db – but I’m convinced the little spring aerials are now the limiting factor – with full power I can now get through 2 stone walls but not right across the house.. but WAY better than the NRF24L01 chips even when the latter have stub aerials.

To run these radio boards, they need 3v3 power. Our Aiduinos run on 5v but have 3v3 out. You can feed the one output from the radio directly but the inputs to the chip might be damaged by direct connection to 5v logic – one option is a level convertor, another is a resistive divider. I found that for the 3 inputs that need it, 470r series resistors do the job just fine (The NRF chips work off 3v3 but will accept 5v signals directly). Why don’t I just run everything off 3v3? Speed and driving other devices, that’s why.

I’ve now modified the Radiohead library so that I can also get a flag when data is passed THROUGH the unit so it’s now possible to indicate the success of not only incoming packets but those passed on elsewhere – very handy for debugging and there’s nothing wrong with pretty lights anyway.

So there it is – what looks like a reasonably inexpensive radio solution for home control and with a tiny mod, the standard Ethernet library handles the Atmega 1284 chips no problem – it’s detailed in here somewhere but boils down to adding the chip to one of the library conditionals for the Mega boards. I did notice when these radios are running constantly, a slight decrease in range of my plug-in-the-wall mains controller handsets as they are on the same frequency range – but in my application, such all-out non-stop transmission would only occur when say the mobile phone is actually polling the units – otherwise it’s just about occasional updates and checks. As for the handsets interfering with the network – they don’t – maybe thanks to the frequency-hopping technology embedded in the boards. Incredible technology for such a low price.

Far more to come in the future. I plan to add moisture detection for our plants, gas monitoring for the home, I already have lighting and heating control working in 2 of the properties. I also have IR remote control and radio mains control underway. Do look in.

This is the latest to date in my series of articles on home control which started with 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 – then came the full mesh article – by this time I had everything starting to run the way I wanted things but for the radio network – as you’ll realise by now, that issue is starting to disappear.

USB Charging Perils

Why should you read this? Are you interested in reducing your USB gadget charging time by up to SIX TIMES? Do you want to fast-charge your phone or tablet as never before?

For some time now the subject of USB power supplies has been in the back of my mind.

How many times do you hear "this is taking AGES to charge"? How many people wonder about their tablet chargers or the leads? Why do some chargers and leads work well and others not?

Well, it’s simple enough really – the more current you put into a device (within limits) the faster it charges – but what’s the bottleneck? Why do car chargers sometimes take ages where a plug in the wall charger might do better?

To start with – the original specification for USB meant that chargers need deliver no more than 500ma (half an amp) and that’s pretty useless for modern tablets with their large batteries. So, there are endless chargers out there which deliver 500ma or much LESS. But unless stated, how are you supposed to know – and in any case, it could be that they’re just not putting enough VOLTAGE out (the specification is 5v but there are tolerances – the cheaper the charger the further off mark it could be – at one end that is dangerous – at the other end you just get less charge).

Then there are the LEADS – some modern leads look pretty (flat coloured ribbon) – but thin leads can mean lost voltage along the length. I’ve seen some leads so thin there is NO chance of them delivering high current.

There is ONE way to test this – simply look to see how much CURRENT is being delivered – then you can check all combinations of your LEADs and your CHARGERS to see what’s best for your phone.

And how do you do that?

If you don’t want to do any messing with meters and razors – simply go to the section called TESTING – you may still learn a lot – I did! But there’s nothing really like first hand experience and results are so variable you really do need to do some testing yourself – but read to the end – HELP IS AT HAND… I’ve already placed my order!


Take a SHORT extension lead which has a full size MALE USB at one end and a full size FEMALE USB at the other (and if it isn’t short, MAKE it short but only if you know what you are doing). The chances are if you open up a USB extension lead with a razor (be careful and only do this when it’s NOT connected) you should see 4 wires inside – red, black, green and white. The latter two are data, the black is ground and the red is 5v. CUT the RED wire – and simply stick a multimeter in the path – set to high DC current.

I did this work for my own needs but you might as well reap the benefit!

tmp8ADETo start the ball rolling simply take a short USB extension (see the image to the left-  note both MALE and FEMALE connectors) and a razor. It is VITAL that this lead is short, say no more than 250mm or so. You don’t want this lead contributing to the problem!!

CAREFULLY cut the lead along it’s length for around 75mm or so, somewhere near the middle – not important where. The idea is to remove the plastic – WITHOUT cutting the leads inside – if you mess them up – bin the lead – get another  – start again.

tmp9230You MAY find a braid inside – or just 4 wires. If the former, fiddle with it until you can get to the wires inside. If you end up breaking the odd strand of the BRAID, it doesn’t really matter but do as little damage as you can. Just make sure you don’t break or damage the 4 wires (red, black, green, white) inside. If the wires are not coloured as stated – BIN it and get another – no point in taking chances – these are dirt cheap on Ebay.

tmpFEE7So now you have exposed 4 wires one of which is RED. Cut it and carefully strip back the wire. Best bet is to shove both ends into a choc-block.

tmpB57AMake absolutely sure you don’t take any strands of braid in there with you – no, really because if you do you’ll destroy the first power supply you experiment on.

So to recap – what we’re doing is BREAKING the +5v lead so we can insert a meter in series with it – and test how much current is flowing with different combinations of leads and chargers.


At this point you’re ready to go. Put the two meter leads into the choc block and make sure you set your meter on AMPS and not milliamps! Mine here is set to 20amps – NO WAY any charger is giving that much out so I’m safe. I can’t advise further here as all meters are different – typically you might have a COMMON connector then one marked AMPS but you’ll need to figure that out.


Here’s the fun and possibly enlightening bit. HONESTLY at this point I had no idea what to expect and was beginning to wonder if this was all worth doing.

I took a typical USB mains charger and typical short black lead – and plugged it into my wife’s Samsung tablet. 550ma.  I then took a fancy thin Chinese green lead – 600ma.  I was expecting the opposite – that’s what I get for thinking – but we’re really not talking much difference.

Sticking with the green lead I then tried different plug-in-the-wall chargers. The second one I tried offered only 380ma – that means not far off TWICE the charging time (obviously – less current – longer to charge) – the Samsung charger my wife had been griping about – ZERO. That’s in the bin.

I then went on to try different chargers…

White Samsung Charger – ZERO

Black Samsung Charger – 500ma.

Black (small) ASUS charger = 600ma.

All-singing Sandstrom dual charger supposed to put out up to 2.1 amps – 350ma.

PC High Power USB 2.0 hub – 450ma.

As you can see – no apparent sense – why would the largest charger not put out the most charge? The little ASUS put out the most. Quite simply voltage – the nominal 5v of these devices has tolerance (variation) and the voltage will vary from unit to unit, manufacturer to manufacturer. So while there are limits to how much current a unit can deliver, if the voltage is too low – you are simply not going to get the current – results will vary from device to device.

So armed with the best charger (for this machine) – the ASUS – I went back to lead testing.

BOY that was an eye-opener – 600ma from my fancy green flat lead from China which I EXPECTED to perform poorly)– but a much shorter, white, very thin Apple-looking lead – 280ma – that’s well under HALF the charge rate and so TWICE the charging time for the white lead.  How does this happen? Well, very THIN wires tend to drop voltage along their length. Some day I’ll make a super testing station with voltmeters all over the place – but suffice it to say that building this rig and testing combinations of your various USB chargers and leads WILL produce results!

I substituted the high power Samsung tablet for my smaller Nexus 7. Green lead 440ma, white lead 380ma – less marked as the current requirement for the Nexus is lower – but still quite significant in terms of charge time.

My Samsung S4 with extended battery – 550ma for the green lead, 270ma for the white lead – again – choosing the latter would potentially DOUBLE charging time.

Sticking with the S4 – I found an old HTC lead – looked a little thicker than normal – WOW – 720ma.  The difference between the worst lead and the best – THREE TIMES.

Now there are lots of things that come into play here and I’ve not had time to do full tests but at least in theory you are talking the difference between a (say) 4-hour charge – and a 12-hour charge – which would you prefer?

So – what if you’re not a dab hand with a meter and razor blade. Well I can’t make any promises but there ARE amazing USB testers out there – some beauties – some with indicators – some with proper displays…

Cheap – so cheap don’t even think about it – just get it.. but it’s not all-singing and dancing…




Or if you want the all-singing impressive type even showing power (which is of course only current times voltage so you could get that from the cheaper ones)…


A tester that shows the voltage at the charger end – and the current running throughout – can tell you a lot about the charger ultimate capacity and the lead.

For my final test – on the Samsung tablet – I tested a VERY short USB lead – around 100mm long – don’t even know why I have it – guess what.. 1.3 AMPS – the difference between charging the Samsung with the WORST lead and the BEST – OVER FIVE TIMES.

Armed with my new short lead – I went back through the power supplies – sure enough – more current than before but still pretty awful – but for one black Samsung charger which now delivered to Maureen’s tablet over 1.7 AMPS – let’s have that in perspective – that is SIX times more charge than the worse case. Pretty damned worthwhile research if you ask me !! 

Here’s my advice – buy a tester  – get short, fat leads – pick the best charger. Simples. 

Have fun.

I’m off to put some leads and chargers in the bin!

A Trip to Jodrell Bank

jodrellJodrell Bank was opened in 1945, a mere 11 years before I was born. Today I’d been at a long meeting which had finished earlier than expected and so I headed off in search of the radio telescope.

For the scientifically uninitiated, radio waves are like light but at a much longer wavelength, well beyond our ability to see as is infra-red and ultraviolet light – but all of these are used when surveying the heavens as they each have their benefits.

signJodrell Bank was in it’s time a world leader by some way – so much so that both the Americans and amazingly the Russians requested use of it during the space race! As you’ll recall the Russians were first up with Sputnik and then a dog – all of this was monitored by Jodrell Bank.

jodrell[7]Ignoring for a second the sheer size of the dish and supporting framework (which turns in any direction) there’s a great visitor’s centre with old Pathe film about the space race right from the beginning and there are a host of things for kids to play with.

It’s a kind of strange mix –on the one hand you have harmless experiments and on the other you’re exposing them to mind-blowing information on Black Holes (it’s not that long ago there was no proof they existed – just a theoretical concept – now it’s all over the place).

Anyway, assuming the weather is half decent it’s worth the £7 entrance fee – there are some gardens there as well and a cafe.

Well worth a trip.


The Return to Rain

Lake in AndaluciaAfter several weeks of flawless weather in Spain, it’s been a struggle getting back into the swing here in the UK where it is raining more often than not. Still I can always look over there using my cameras to remind me of the sun.

Meanwhile, after months off due to a death in the family and then a broken foot (you can’t make this stuff up) Maureen is now back to work and meanwhile I’m about to embark on a series of meetings taking me from Blackpool to Crewe and onto London. It’s going to be a busy week.

Over the weekend I’ve been catching up with emails, finding out what’s going on at work – and doing a little more research into my home controls as well as catching up on episodes of “Cosmos” – which I intend to continue this week as I’ve loaded up the tablet with remaining episodes to catch late at night in my hotel (well, it beats hotel TV). Got the Bluetooth headphones all charged up and ready.

While we were in Spain I ordered a pair of cheap SI 4432-based 4.33Mhz transceivers and I had high hopes for these after the abysmal results I’ve been having with 2.4Ghz radios thanks to interference from WIFI, cordless phones and a thousand other sources of radio crap.

This weekend I tried the PA-enhanced version of the NRF24L01 radio to help me expand my home control setup – one worked – the others failed as they often seem to do – I can’t get to the bottom of it other than to suspect there is an issue with SPI (communication) speed and these radios – as the cheap ones work every time. Others have said similar. Having abandoned the more expensive types, I used my air gun to remove the aerial from one and grafted it onto one of the cheap versions. As you can see in the image below, it looks ok – simply a matter of cutting the original aerial track – 5 mounting holes and a couple of VERY short wires.

NRF24L01 Peter Scargill modification

I can say for sure that the aerial-enhancement modification is robust and improves range – but I doubt it it even doubles the range which still remains pitifully short in a stone building – and of course the cost to buy these adaptors and aerials individually far exceeds the cost of them as part of a radio!

SI4432 radio moduleI then tried the 433Mhz units which came complete with a coiled spring aerial.  I carefully put two of these units together using our Arduino look-alike boards. These are not easy to use as the edge connector is 0.05” centres – you really need a fine soldering iron which I just so happen to have. Despite all that, I ended up with one board (apparently) working – it the code was working – but the other remained defiantly dead. So many things could be wrong – the code, the wiring, the interfacing… these are 3v3 boards and my Arduino clones are 5v. I fed the boards with 3v3 and ran the inputs to the radio via resistors. I’m pretty sure that part is correct.

tmp7FADIn the process I found a bug in the Radiohead library I’ve been using and the authors fixed it almost immediately which is nice.

The end result looked a little messy due to wiring and resistors – but actually I was quite pleased with the overall fit for a first attempt – not so pleased with one unit apparently dead.

When I checked, the other board had 2 pins shorted – no matter what I did I could not find the short – I can only imagine it was under the 0.05” connector – even a magnifying glass showed no issues – and attempting to remove the connector with the air gun resulted in the board’s destruction. I now have a 2 week wait before I can progress this one (not that it matters as I’m in meetings for over a week). The hope is that these 433Mhz units will have a better chance of going through thick stone walls – I’ll have to wait and see. Next time I’ll nix the connector.  I’m also interested in the new cheap WIFI embedded units which can be bought from Ebay as low as £8 – for now however both the embedded software and the instructions are in Mandarin so that will have to wait a while.

In a couple of weeks I’m going to spent time with a friend as we examine the powerful Atmel radios, not in the same price class but it’s worth exploring all avenues.