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


Information Displays – Part 1

As part of my home automation experiments I want a way to display the current state of sensors or currently active events on an LCD screen and install the LCD screen (or screens) in convenient locations round the house.

The basics requirements of what it should be able to do are as follows

  • Show a prioritized list of currently active events with columns such as priority code, message, elapsed time, etc.
  • Each priority should have configurable colors (foreground/background/flash), sound (file, repeat)
  • Show the current date and time
  • Show some basic status of the application (offline, online, etc) in case a connection to the server is not available.
  • Show the current value of sensor/value type points (temperature, humidity etc)
  • Configurable background image(s)
  • Be able to run in full screen mode (i.e when installed on the wall) or window mode (easier for development or running on the desktop)
  • Be able to auto start the application when the machine boots up if required.

Nice to haves

  • Full screen mode – try to blank the screen when no-one is in the room?
  • Perhaps go silent when no-one is at home?

More things I’m sure, but can’t think of anything else at the moment.

Initial Use Case

The initial use case is to display a message and play a doorbell like sound when my doorbell is pressed.

For reference my front door bell is a wired switch connected to an input module. The input is configured as a momentary input, with a 10 second timer (see input #9 in the screen shot). When pressed the event makes its way to the server for other applications to see.

 CAN Input Module Setup


It sounds possible to implement this in a web browser but being lazy I cant be bothered to learn the latest html5, json, web socket, bootstrap, blah, blah, blah technologies … so initially I go with what I know best and implement this as a .NET application and leave a web version for another time (i.e. probably never) 🙂

Endless Revisions

I find when I’m coming up with my own hardware designs there’s always something else that would be nice to have, could be better,  or just different. Most likely it comes from having no fixed set of requirements up front. Perhaps the exact end application isn’t exactly known ahead of time as sometimes happens when trying to design generic items.

To this end I present the endless revisions of … the CAN input module .. over 7 years (yay for date codes on the PCB silk screens)

2006-05 CAN bus, 16 isolated digital inputs, DIP switch pull ups for each input, hardware debounce, unique ID chip, large aluminium enclosure, large 5mm plug and socket connectors. This version I threw everything in but its just too big and the cost was just too much mainly due to the enclosure but also the number of connectors. I never got around to doing the PCB end plates.


2006-11 CAN bus, RS485 bus, 8 non-isolated digital inputs, 8 open collector digital outputs, unique ID chip, small plastic enclosure, large plug and socket connectors. I think this one was modelled of the popular ADAM4050 module from Advantech. Simplify everything and reduce cost. It’s almost 1/4 of the size of the previous module and much less parts. Still just having the plastic case makes it ugly to install anywhere and look nice. Again I never got around to doing the PCB end plates.


2012-10 CAN bus, 16 non-isolated digital inputs, DIN rail plastic enclosure, screw terminals for inputs and RJ45 for CAN bus. Skip forward few years, I guess sometimes you never get a project “quite right” and you just have to do another revision. This one got most things correct in my mind. Cheap to make, single purpose by removing the outputs, nice to install on a DIN rail and standard CAT5 for bus interconnect and power. The case has a nice recess for the label for all the relevant installation details which is handy.


… but there is always something else … I was writing the firmware and saw that I could use 8 of the inputs as digital or analog inputs – so another revision …

2013-04 CAN bus, 16 non-isolated inputs, the first 8 can be optionally configured as analog inputs, internal pull up or pull down jumper for the analog inputs, DIN rail plastic enclosure, screw terminals for inputs and RJ45 for CAN bus.


Its 2014 and surprisingly I can’t think of anything to add feature wise, but that doesn’t mean there isn’t something else … that can be a topic for another post.