You Can Never Have Enough Sensors

Day 1

What to do today now the lawns weeds have been mowed? The solar powered sensor is back out in the garden and seems to be working and recharging its battery in the sun today. The receiver is pumping the data into Xively nicely. I have these bits laying about …

  • 2 x Arduino TwentyTens
  • 2 x nRF24L01 modules
  • 2 x ProtoShields
  • 2 x 10K NTC sensors
  • 2 x Dallas 18B20 temperature sensors
  • 2 x Light sensors
  • 1 x DHT11 humidity sensor
  • 1 x BMP085 pressure sensor
  • Plenty of time

Parts Please

Yes its pretty obvious – more RF sensors. Might also be handy to do some indoor range testing and a network/mesh of the nRF modules.

Day 2

Today I partially assembled the two prototype boards. So far the LDR and DS18B20 are fully functional, and the nRF module is soldered in place but not yet wired up. Looks neat and tidy.

Partially Assembled

Of course now it is partially assembled its always nice to know if everything is working. So here is some simple test code. Same story and usual, Google for some existing libraries, no need to write your own.

I ended up with these OneWire and Dallas Temperature

And the output (including other debugging not in the code)

Day 3

Another day with progress. Today I wired up the nRF modules and added some more code to send the readings to the receiver. Other than a snafu with one incorrectly wired pin, it all went without other issues.

Here is what the protoshield looks like now. Still pretty neat. I added the 10uF cap to the 3.3V line, cant remember why or if it is really needed, but my receiver has one so I figured it can’t hurt to have it installed. Yes the wires I have used (single cores from security cable) are really too think for anything too elegant but it was all I had laying about.

Radio Installed

Latest is now live on the Xively Stream.

  • 1000 is the external sensor in the garden
  • 07f3 & d1ad are the new internal sensors

Next up, Add the screw terminal and send readings for the remote NTC temperature sensor …

RF Sensor Ethernet receiver

Feeling inspired by writing up the last post I decided it cant be that hard to convert my USB receiver into an Ethernet based one.

My USB implementation was using an old Freetronics Twenty Ten (the Eleven seems to be the latest equivalent) with one of the nRF modules soldered onto a ProtoShield Short.

I didn’t want add more shields as things start to look ugly so I happened to have an EtherTen in my Arduino parts box so in theory its just swap the shield to the new base board, change the code to add the ethernet connection and all done! That’s the theory anyway.

Like all good theories it wasn’t that simple. The pins I happened to choose for the nRF module conflicted with the pins used for the Wiznet chip for Ethernet connectivity. No matter, I rewired the offending pins and changed the code to suit – fixed.

So the firmware connects to network and the sensor readings are being received, all working great – but where to send the data to?


While I’d eventually like to have the data stored and processed locally, Xively seems like a choice to get things up and running with little fuss. I can let the receiver run 24×7 for testing while I sort out something more permanent locally – or if Xively does all I need that it can stay there – meh at this stage who knows.

Anyway, the developer section of the Xively site is pretty simple, find and download the Arduino library from git add it the the Arduino libraries folder and your away.

Total integration time was less that one hour including some optimizations.

Here is the public link for the prototype.

  • 1000.01 Temperature Sensor 1
  • 1000.02 Temperature Sensor 2
  • 1000.03 Light Sensor
  • 1000.08 Battery Voltage

The format is of the channel is XXXX.YY, where XXXX is the transmitters serial number, and YY is the sensor input number on that particular device.

Xively Test Data RF Ethernet Receiver


You can see the setup is nice and compact but I don’t like that I cant use the POE adapter board and a shield on the EtherTen at the same time so I still need to power the device from USB or the DC jack.

The nRF module is pretty much sitting over the shielded RJ45 connector which is probably acting as a ground plane – so not ideal.

Anyway for now I have a handy 12VDC source readily available so I’ll hook up the DC jack. Then I don’t need to have it connected to my desktop PC all the time – except for debugging.

Update: Things have gone fine expect for an outage at exactly 9 PM one night. Not sure why – but the timing seems to perfect, perhaps the DHCP lease expired?

I changed the code to renew the DHCP lease and left the debugging output running to hopefully catch something. Could have been a random power issue resetting the Wiznet chip – who knows.


Whats The Temperature?

What is the temperature outside now? In the pool? Inside the garden bed? How much light did we get today?

To answer these marginally useful questions the obvious solution is to build a solar powered, RF transmitting sensor – paired up with an RF receiver to act as an interface to the computer.

First thing some basic requirements

  • Multiple temperature sensors
  • Simple light sensor
  • RF transmitter/receiver pair or transceivers
  • Solar powered – implying battery powered
  • Able to run 24×7
  • Weather proof/resistent
Sourcing the Parts

Again better not reinvent the wheel so after a few Google searches and numerous distractions I found the Seeeduino Stalker.

Seeeduino Stalker

A nice starting point to get the main things I needed. In particular the Arduino board with solar input, lipo battery charger circuits, a cheap solar panel, a lipo battery and importantly a waterproof case ready to go.

I got a Bluetooth XBee module for quick testing as I already had a USB Bluetooth dongle so I could get something up and running pretty quickly without needed to prototype the receiver.

Now some cheap temperature sensors – Aliexpress has many options here. I went with some cheap 10K NTC resistor based items. I didn’t hold much hope about sticking these particular ones in the pool (salt water / chlorine) on inside the garden bed (moisture in general) but its a start and at the price  they were cheap enough to be disposable.

The light sensor was just an LDR I already had in my parts draws.

Cheap 10K NTC Sensor

 Initial Setup and Results

I put some quick firmware together and as it was summer time with plenty of sun around I stuck with using Bluetooth as the communications put it all together and installed in by the pool with one temperature sensor dangling in the pool and the other just in free air.

Setup 1


Unfortunately I don’t have an image of the sensor that was in the pool – it lasted maybe a month before the temperature readings starting dropping – it appeared that the potting compound wasn’t really adhered to the wires and eventually the salt / chlorine / heat got into it – not unexpected.

The Bluetooth was marginal from the pool to the office – maybe 17 meters away and through a few walls and metal window shutters – not unexpected.

The battery recharging worked quite well – it was full Adelaide summer after all, weeks of 35+ degree days with no clouds. The graphs of battery voltage did indicate that the battery was pretty much marginal as is each night it almost expired only to be saved by the sun the next day.

Happy with the initial results none the less as I hadn’t done any power optimization at all.

 Autumn Radio Upgrades

The initial prototype was retired after summer as the battery drain from the Arduino and Bluetooth modules running 24×7 was just too much. Plus the pool isn’t heated and there was little interest in the water temperature – you already know its cold. Naturally it was time for an upgrade.

I have no idea how much power the Bluetooth module required as I didn’t measure it properly but my assumption of power usage and the range being quite poor I decided to upgrade the to some RF modules. An obvious and cheap choice was one of the numerous nRF24L01 modules you can source just about anywhere these days. $10 for 10 transceivers is very hard to beat so its worth a try.


There are plenty of Arduino libraries out there for these modules so changing the code over was also pretty straight forward. I also needed to make a receiver in the office to get the data sent from the sensor.

Here is the sensor at the bottom and receiver at the top as it is now.

The winter kit

It was now autumn and there was still enough sun during the day to keep things running overnight even though the Arduino was still running 24×7 at full speed (8Mhz). At this point I was already powering down the nRF module in between transmissions to save power.

Winter Firmware Upgrades

Winter comes along and the amount of sun during the day – assuming there is any at all – is just way too short. So time to finally get the firmware to do proper power management.

Lucky for me the Stalker board had an on board RTC. The firmware basically uses the RTC to set an interrupt/alarm every minute, wakes up, takes the readings, sends the message, and goes back to sleep.

The results were much better – lasting over a week with little sun and the panel flat of the ground – less than ideal. Here is the graph for the last week.

Weekly data

Something Still Obviously Wrong

You will notice the graph is quite sparsely populated – to say the least. The sensor is pretty much outside my office window about 4 meters in the garden bed. The receiver is on my desk. At night the metal window shutters get closed and the sensor readings tend to disappear – not unexpected but annoying.

I think this is a problem with using the nRF modules, at least these ones with the PCB antenna. Some problems I have seen

  • The angle at which I have the transmitter and receiver matters. Flat seems worse than upright.
  • The range I get from the modules, while good, just isn’t good enough to reliably have communications from outside to inside, let alone from one side of the house to the other.
Future Upgrades

For now it will suffice but some future upgrades will include …

  • Using a receiver with the nRF module that has the built in amplifier and normal antenna.
  • Mounting the receiver on an outside wall to eliminate the metal window shutter problem.
  • Using an POE powered + Ethernet enabled Arduino for the receiver and upload the data to a server rather than having the receiver connected to my desktop PC.
  • Creating a few more sensors for around the yard
  • Finding a solution for a pool water temperature sensor.
  • Having the data available and graphed on a website so I can check whats happening from anywhere.
  • Add a soil moisture sensor
  • Add a humidity sensor
  • Integration with my watering system


Alarm Panel – Programming settings

With the interface installed I needed an easier way to program the settings. Having to recompile the Arduino code each time you want to change something is pretty poor.

The V2 firmware supports

  • 16 zones, each with
    • Name (15 characters)
    • Enabled flag
    • Alarm flag
    • Cancel flag
  • 4 phone numbers, each with
    • Number (15 characters)
    • Enabled flag

Nothing too complicated but enough to get the job done. All the settings are stored in the EEPROM of the Arduino (atmega2560).

First thing I wanted was a simple command line interface. Worst case all you need to program the interface would be a terminal (something like Putty, TeraTerm, HyperTerminal, etc).

Being lazy its always easier to see if something already exists before you roll your own. Even if its not exactly what you want you can get some ideas. Lucky for me, with a few Google searches, I found the serial command library.

So simple, install the library, include the header, add a few lines and a few callback functions – done!

So now via the command line we can

  • enable/disable debug mode
  • update zone data
  • update phone data
  • display the current information
  • enter setup mode
  • turn on/of SMS message sending

This is enough really for the prototype – but – if you want to make it a bit easier for the average Joe to use then it’s time to a make a simple UI.

Behold – the alarm interface programming tool. Of course it looks like crap but it gets the job done. Simple operation Read the data, modify the data, and then write the data back.

Under the covers it uses the serial commands we defined earlier to to read and write settings. The hardware version and firmware versions do work but not in this early screen shot.

Program some settings

Cool – simple programming tools done – now to customize for my alarm panel and see if we get some SMS messages out!

Alarm Panel – SMS Interface Installation

For what seems like forever Simon and I have been working on an alarm panel to SMS gateway device. Mainly to be used with an existing alarm panel, this device will plug into the phone line socket of the alarm panel, allow the panel to “call” and then respond with the proper Ademco tones.

Click here for Simon’s blog posts on the hardware design.

With prototype V2 finally complete and the latest firmware uploaded it was finally time to give it a test run on my alarm panel. Now how to mount it and monitor it for testing? Here is all the stuff where I need to make it happen. Seems like a mess before I even start – this was after I cleaned up the original mess – sigh.

Alarm SMS Items What a mess

  • Alarm panel, alarm SMS interface, phone cable and GSM antenna
  • Raspberry Pi and USB cable for debug interface monitoring
  • 5V switch mode power supply module for the RPI
  • 12VDC Plug pack for the home automation gear
  • 12VAC Plug pack for the alarm

I decided to remove all the existing items from the wall and remount everything on a sheet and MDF. That will make it easier to mount things without the need to locate any wall studs. I roughly measured the wall area, alarm, RF receiver, and power point locations. Marked them up on a piece of MDF the let rip with the drill and jigsaw to get the power point hole removed.

A - Markup B - Drill C - Jigsaw

Looks nice, let’s hope it fits! Of course it did, was there ever any doubt? Now to remount everything. It all went pretty much to plan for a change. The alarm panel was slightly painful as it didn’t really have a lot of movement but some handily placed boxes took care of that.

It fits Remounted Almost done

I rewired my automation input module and finally installed the alarm SMS interface and RPI ready for testing.

Remember this is for testing so yes its all just spread over the shelf for now, the proper installation will not have the RPI and the interface will most likely be mounted inside one of the two cases with just the antenna on the outside.

Now finally I can start testing !



Code Generation Tool

Having to write a lot of simple code once can be tedious and error prone – having to write it again for another language is even worse. Having to maintain both is just plain stupid. It would be quite handy to use a tool to generate all this basic code for us.

In my case I want the tool to create my standard code for my home automation software. I started with Java code but wanted to do an application in .NET and I didn’t want to port* or maintain both code bases – especially if the exact specification was still work-in-progress.

* Porting of the underlying base CDEF library was needed of course.

  • plain old data objects
    • fields can be
      • basic types (int, long, string) or other objects
      • lists of basic types or objects
  • messages
    • requests and responses
      • fields can be
        • basic types (int, long, string) or other objects
        • lists of basic types or other objects
      • encoding and decoding of data into byte buffers
  • languages
    • Java
    • .NET

The input to the tool is a form of specification defining all of the details and I chose to use XML to represent this data. Below is a very basic example of a simple class and message.

Running the tool and generating the code gives me the new source files. Note that the CdefMessage class is essentially a byte buffer. There is a constructor that pulls the data out of the message and an encode function to do the reverse.

In Java we get the same thing more or less. Ordering of encoding and decoding each field is important so we can send the objects between applications written in either language.

Here is the .NET Error message code, the Java is much the same. You can see how I handle lists of data objects and how they get encoded and decoded as required.

There are a few other helper classes that get created to make everything work but already we can create all this basic code with very little effort, no mistakes and knowing that both language libraries are in sync. This suits me as I’m very lazy and the less I have think about the better.

Wall Switches Redux

Another side track/experiment

As part of my obsession with finding the ideal wall switch, I found these Livolo brand switches via Aliexpress. Aliexpress seems to be the “go to” place to find just about anything these days.

I ordered one single switch version VL-C301-81 and one four switch version VL-C304-81. Both without the option radio interface or the A/B switching options. The radio interface, after thinking about it, would have been quite handy–  oh well, they are cheap enough to order more if required.

Why these ones? Looking at the marketing images on the Aliexpress pages seemed to show that they are relatively simple in design, with an upper and lower PCB connected with standard headers. A nice point to be able to hack into it. Also of note to the hacking people among us one of the images showed that the top PCB appeared to have a PIC processor on board – hmmm.

Livolo Assembly

The idea was buy the switch, remove the original back PCB (the one that does the 240V and relay stuff) and substitute my own low voltage PCB – with simple connectors or more advanced CAN interface. The top PCB hopefully wouldn’t be any the wiser. The end result would be a nice looking touch switch that hooked into my home automation system.


The single switch plate went into service replacing the standard Clispsal switch my FutureTAB HQ office.  Installation was quick and easy – just make sure to turn off your breakers before playing with any mains voltage stuff – or better yet get an electrician to do it for you.

Another reason I want to replace all my switches with low voltage equivalents and have other ways to flick the mains to the lights/appliances/etc. I hate touching anything with mains involved.


I like the way they work. The touch area is quite tight around the indicated circle. The blue “idle” LED is very dim, barely visible in the dark, but it is far easier to find the switch in the dark. Generally blue is an annoying color, especially if its bright and/or in your face, but this one could have been a little brighter – maybe a hack for later. The “on” red LED I really can’t see when the light is on – so maybe its useful, maybe not – again maybe a hack to make it brighter. The relay clicking is no louder than a normal Clipsal switch – so nothing to gain there. It is also easier to turn on the lights when my hands are full with food/coffee/etc – less chance of spillage accidents – bonus!

I have a home theater sub woofer with one of these annoying bright blue LEDs – it has a  strategically placed piece of tape covering it up – A bright blue LED shining in your eye while watching a movie in a dark room — WTF were they thinking?

“Don’t Turn It On, Pull It Apart” – EEVblog

In my case I say turn one on, take the other one apart!

The photo above was exactly what it was inside – how nice of the Livolo marketing folks. The photos below show the top PCB that I want to interface with. Clearly visible are the four LED and touch switch areas with some clever use of the silkscreen underneath the clear plastic parts to aid in light reflection. The bottom of the PCB shows the PIC16F960 and the 14 way header used to connect to the bottom PCB. They have even included what looks like a PIC programming header – hmmm.

 Livolo Top PCB A Livolo Top PCB B

Stay tuned for details on how I go with the hacking experiments.


Wall Switches

Over the last few years another obsession has been low voltage wall  switches The requirements for a DIY home automation wall switch sounds simple enough.

  • low voltage (either pull up to V+, or down to GND)
  • momentary
  • control lines for an LED per switch (off / on)
  • look decent enough for family approval factor

The idea was to connect this switch to an CAN Input Module (switch) and CAN Output Module (LED) and then use the CAN messages to “do stuff” like turn on lights, etc, etc

I spotted these WattStopper LxS switches after a lot of searching the web. I ordered one of L5S ones to experiment with – tricky in itself to find somewhere to order it from that would deliver to Australia. It has 4 thin buttons and 1 larger button, momentary, and a single LED for the 4 thin buttons. So almost a match for the requirements and the closest I have found so far.


WattStopper LxS Switches

It’s not until you have it in your hands that you really think how you will hook it up …

Problem 1 – Electrical

The switch did not suit hooking up to my input/output modules directly. With all the redesigns of the input module I still didn’t have what I needed – typical. I pulled the PCB from the switch and modified it slightly to suit my needs – no big problem but you really don’t want to have to do this for anything but a prototype.

Problem 2 – Practicality

I didn’t think about it until I went to wire it up on the bench – to fully utilize this 5 button switch you needed 11 wires – 2 x 8 core CAT5 cables or 2 x 6 core security cables. Cable is relatively cheap, and if you’re pulling one cable, pulling two isn’t that much harder – but it still seems like a waste of resources. In the picture I have only hooked up the top 4 switches and the locator LED.

WattStopper Partial Hookup


One solution is to add smarts to the switch so it does what you want by replacing the stock PCB with my own PCB design. This way I can add the CAN bus directly to the switch, use RGB LEDs and so on. I don’t really like the idea of buying something only to throw part of it away.

Another solution is to make my own PCB and fit it to another standard wall plate – this has its ownset of problems and will be the topic for another post.



Information Displays – Part 2

Time to code … I suspect it wont take too long to get something up and running. For this I will use Visual Studio 2013 Express and code in C#, that way anyone can grab the code from Github and use it for themselves.

Get The Screen Up

LCD screens come in all sorts of resolutions and sizes, so to make this useful we need to able support different configurations. For development and testing we probably want it to run in window mode with smaller fonts, if you have a multi-screen setup maybe you want to to run full screen on your second screen, for installation full screen with larger fonts sounds good, portrait mode maybe?

I chose to have the configuration in an XML file so its relatively easy to edit and parse.

I added the ability to specify the background image at this point. Nothing particularly tricky so far but it loads and re-sizes the form,  and goes full screen on the required screen if needed. 

Adding Some Labels

We could just add Label controls to the Form inside VS2013 but that doesn’t really allow us to change the layout for our different setups. The simplest way to add text to the screen will be to define labels in the XML – It will be slightly painful to do x, y, width and height maths in your head but it will do for now. Hint: Someone could write an WYSIWYG editor I guess or something else?

Initial Label Types

  • static – Just static text – well duh
  • time – Using a timer update the label and print the current time in using the given format.
  • file – Update the label with the contents of a file with configurable refresh rate.

Check out the screen shot so far in window mode. The temperature, light and voltage data is read from files created by another application.

Next up well add code to connect to the server, and display the currently active events in a configurable “list like” view.

 Display Part 1

Configuration Part 1