Push buttons as input

Tags: , , , ,
No Comments »

imageTo control the lights in a house or in my own apartment switches and buttons near the doors in the wall are a very useful thing.

Even if my home automation can be controlled by ethernet, mobile phone, timers, you name it, it will be most convenient to use normal switches, too. I was lucky to rewire the whole apartment and I decided to  put a separate wire for each switch to a central place where my home automation controller will be placed.

I will use push buttons instead of on/off-switches. Push buttons can be used for multiple commands. Starting with turning a light on or off, you can program it to do different actions when pressing just for a short or a longer time. Or you can do a continues action as long as the button is pressed down.

But first of all the signal from the buttons needs to be received by my micro controller. I will use 12V DC for all buttons, to avoid higher power like 110V or 220V AC. To protect the electronics and don’t get trouble with long wires at all I use optocouplers. Basically the 12V from the push button just turns on a small LED within the optocoupler from where the signal takes its way.

The schematics

The signals itself are received by a PCF8574 I/O-chip. This chip comes with 8 digital I/O ports and an I2C interface. The microcontroller can query the state of all I/O ports using the I2C interface. As a bonus the chip triggers an interrupt each time any input signal is changed.


There is nothing fancy at the schematics, just read it from right to left. At the very right you will find 8 inputs for the 12 V from my pushbuttons (and the GND used with this signal). Following by the optocouplers. To use more or less then 12 V just adjust the resistors value. The rest of the schemantics are just pull up and down resistors and some more connectors for the I2C bus.
The board will be build in a way to chain multiple of this boards together. The I2C bus goes from one to another.
By using the solder jumpers SJ1, SJ2, SJ3 you can select one out of eight addresses. Each board comes with its own interrupt on connector JP2.

The board

As above you can find the connectors to the push buttons on the right. You will see the two quad optocoupler chips in the middle and the I2C I/O chip at the left.


I have four of this boards connected with nearly 32 push buttons. They all share the I2C bus which is connected from one to another (see the small white, red, green and yellow wires at the bottom). But each provides its own interrupt signal. So for the whole installation the microcontroller only needs four IRQ ports and one I2C bus.


The code

Will be the topic of my next post. Stay tuned.

What is this all about

If you find this post interesting, have a look at the other posts in my homeautomation category within this blog. Especially the first and the second post describe what this is all about.

The schematics and boards (created with EAGLE) and all source code is or will be available on github: https://github.com/irgendwienet/homeautomation

Power, I2C and DMX

Tags: , , , , ,
No Comments »

The first board for my home automation project needs to provide everybody with Power (5V DC). This is the main purpose of this board and because this is a very basic requirement it’s the first to be described here.

But this board handles two more jobs:

  1. create 5V DC from input voltage of 12V DC
  2. convert a 3,3V I2C bus to an I2C bus capable of speaking with 5V components
  3. driver for the DMX signals


Here’s nothing special. Just a P3596L-5.0 step-down DC/DC converter, two capacitors, an inductor and a diode.

06-01-2013 13-32-58


The microcontroller I’m using only has 3,3V output pins even if they are 5V tolerant you cannot connect 5V I2C components. But the rest of my setup is build with 5V components so I have so power up the I2C-Bus accordingly.

Luckily there is a chip that does the exact same thing: the PCA9306 a dual bidirectional I2C bus voltage-level translator.

It just needs a 3,3V (I get this directly from the microcontroller board) and 5V current and the input I2C bus. No big deal at all.

06-01-2013 13-59-50


DMX is a protocol used on stages for controlling lights. I use the same for dimming my LEDs in the whole apartment. Today I will not go in much details about the protocol or the software side.

On the wire DMX is just a symmetric RS-485 signal on three wires (called + / – / GND).

I use a simple SN75176 differential bus transceiver chip but since DMX is only sending in one direction there is no need in using the receiving side of the chip. The control ports are hard wired for sending and it gets its signal from an UART of my microcontroller.

On my board I put three of the same chips to create three physical separated busses with the same signal.

Again, here is less magic involved:

06-01-2013 14-06-32

The Board

06-01-2013 14-07-25

From left to right: Power / I2C / DMX

What is this all about

If you find this post interesting, have a look at the other posts in my homeautomation category within this blog. Especially the first and the second post describe what this is all about.

The schematics and boards (created with EAGLE) and all source code is or will be available on github: https://github.com/irgendwienet/homeautomation

State of the art: my home automation

Tags: , , ,

It has been a long time since my first post about home automation in my new apartment. And now it’s time for a wrap up what’s going on here. First of all: most what is described in that post is implemented and up and running for more then one year now.

So let’s have a look at the basic setup that’s in my closet:


Or as an easy to read schematic:


At the bottom you find the FEZ Cobra board. That’s the µC-board or the heart of everything here.

In the row above a simple 12 V power supply can be found, two cards of output drivers for the relays and a card with multiple purpose: Power regulator, I2C voltage converter, DMX driver.

The blue rows contains 16 relays switching 220 V DC lights within my apartment. This is the only part of my whole installation where the power is more then 12 V. So be careful when touching here.

At the top row four cards with each 8 input ports with optocouplers can be found.

I will describe all parts in futures posts in detail.

Do it yourself: home automation

Tags: , , , ,

For my new apartment I imagine some nice (or nerdy) infrastructure things. Since the apartment is currently building and I can decide how to do the wiring: we will get CAT7 Ethernet nearly everywhere for gigabit Ethernet. We will get a lot of power outlets, HDMI cables from the stereo to the TV and to a potential place for a projector and so on.

I was also looking into systems for home automation to control lights etc. using some commercial bus system like KNX. But all these systems are boring, expensive, inflexible and absolutely not the kind of system I was willing to invest a few thousand euros in. They advertise all that stuff as programmable and ultra flexible. But you need some expensive software and special adapters to reprogram your house. To save light configuration and recall them by a button you need some light-configuration-controller-hardware (at about 200 Euro) and a guy to program it. Non of the classical home automation systems can be controlled with an iPad.

So I decided to build something for my apartment by myself. In this first post of many I will show you my basic ideas and later I’m planning to publish hardware schematic and software source code for single modules and maybe for the whole thing.

The goal

  • Control every light in every room of my apartment
    • some will just turn on / off
    • some are dimmable
  • Controlled by the regular light switches
  • A “Turn everything off” switch at the main door
  • Connected to my local network (e.g. webservice)
  • My personal application on an iPad

optional (or later on):

  • Control the motor for the projection screen
  • Control light by timers
  • Send infrared signals to the stereo and the tv set
  • Connected to the phone line (e.g. turn off the music when the phone rings)
  • Receive data from wireless sensors
  • Add a sensor to the washing machine and remind me when it’s finished
  • much more

The basic concept

To control all this I will use some central microcontroller in my apartment. I decided to give the Microsoft Micro Framework a try. Since I’m already a .Net guy it should be pretty easy (and cool) to program my home in C#. I will use the FEZ Cobra board. A 72 MHz ARM device with 12 MB RAM. It is probably already too powerful for my usage but who cares. It comes with USB-Ports where you can connect keyboards, joysticks or cameras. It has a build in Ethernet port, a SD-Card slot a lot of I/O Ports and everything else you need. One could also connect a TFT touch screen. With this guy I have all the connectability I need and enough power to implement all crazy ideas in software.

In the walls I will get push buttons instead of regular on/off switches and a single cable will be used for each of this button to a central place where my project resists. This way the Cobra board can receive signals from all buttons.

To control the lights the cables will be put to these place too. Here I will use relais or dimmers controlled by the Cobra board. For some lights I will try RGB LEDs with DMX controllers (I will later explain what that exactly is).

A little bit more in detail

The key to all this is my custom wiring with a lot of more cables in the walls then usually. Since the apartment will be newly build I can get this wiring without big problems.

My push buttons will be powered only by 12V or 24V DC not 240V AC (the normal power in Europe). This way it is much easier to connect it to the Cobra board.

For controlling dimmers I will use dimmers with a control input of 0 to 10V. Again: it’s much easier to buy some working and proofed dimmers for the 240V high voltage and my DIY projects only controls it by a 10V signal. The same for switches: the Cobra board will drive some relais with 12V DC and the relais will switch the 240V AC line.

Maybe I will use for dimmers and other light controlling stuff the digital DMX512 protocol. This is used on stages to control all the light effects and seems pretty simple to implement on the hardware and software side.

For most of these functions I will create small hardware modules and connect them to the Cobra board. This way the completion of the whole project is much easier. Some of these modules will be connected to the I/O ports of the Cobra directly and some will use a I2C-Bus.

Some modules first

To get stared I created hardware prototypes for the first modules of the system. These modules can be used for the purpose I’m planning or for something totally different (at the end these are only input and output port controlled by a microcontroller). I will show you the different modules in upcoming posts. Once finished the major parts I believe I will extend the whole system step by step. But let’s start with:

  • I2C voltage converter
    • since the Cobra board uses 3,3V but all other modules will use 5V I need a simple voltage converter
  • I2C input module for push buttons
    • using optocouplers and an I2C-I/O-chip
  • I2C digital output modules
    • with an I2C-I/O-chip again and some drivers to power relais
  • I2C analog outputs
    • to create the control voltage for 0-10V dimmers.
  • DMX512 output


Within the next weeks I will start to write a post to each of these modules with detailed hardware and software explanations.

WP Theme & Icons by N.Design Studio
Entries RSS Comments RSS Log in