{"id":1444,"date":"2014-11-14T00:00:04","date_gmt":"2014-11-14T08:00:04","guid":{"rendered":"http:\/\/192.168.3.4\/?p=1444"},"modified":"2018-01-09T06:49:50","modified_gmt":"2018-01-09T14:49:50","slug":"command-and-control-as-easy-as-pi","status":"publish","type":"post","link":"https:\/\/www.cloudacm.com\/?p=1444","title":{"rendered":"Command and control as easy as RPi"},"content":{"rendered":"

Introduction – dedicated to a specific task<\/strong><\/p>\n

The HVAC system in any house is a great starting point for home automation. \u00a0This is commonly used in practically every home in the US. \u00a0The heat or air conditioning part my vary from state to state, but the system as a whole remains standard. \u00a0Controlling the HVAC system using RPi<\/a> is a great way to learn the RPi platform and enhance your home.<\/p>\n

In this section, we’ll take inputs from thermostats and temperature sensors to control the actions of the RPi. \u00a0We’ll continue on by activating fans and heaters based on parameters we set in the RPi. \u00a0Next, we’ll read values provided by data sources\u00a0on the internet to enhance our control actions. \u00a0Finally, we’ll wrap up the section by posting out to internet hosts\u00a0so the public can view the results, without giving them direct access to the critical HVAC system.<\/p>\n

You can refer to the RaspberryPiIVBeginners<\/a> Youtube channel to get an introduction\u00a0to RPi input and output control. \u00a0Matt has done a bang up job.<\/p>\n

Purpose – the wheel has already been invented, how can we make it spin with less effort<\/strong><\/p>\n

HVAC\u00a0control systems\u00a0have a price range that scale with feature and reliability. \u00a0The goals\u00a0of automation are comfort, cost savings, conscientiousness consumption, and ultimately\u00a0energy efficiency. \u00a0 The use of a RPi to handle the ins and outs is\u00a0a perfect fit in understanding what the RPi can do. \u00a0It can help to achieve these goals.<\/p>\n

In this example, the RPi will be tasked to do these operations.<\/p>\n

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  1. Read input from a thermostat or\u00a0temperature sensor\u00a0and represent it accurately.<\/li>\n
  2. Send an output to control a device , such as a fan, pump, or heater\u00a0with reliably.<\/li>\n
  3. Send data to a network host for it to present on the internet.<\/li>\n<\/ol>\n

    Once we have these key functions operating, it will become clear why the RPi is a better choice than a micro controller. \u00a0Simple IO and math functions can be handled by micro controllers, but we’re after more. \u00a0We’re looking for a better understanding why the system does what it does, so we can make better design choices.<\/p>\n

    Detail – fitting the RPi in and getting it in the middle of it<\/strong><\/p>\n

    Some basic features\u00a0should be setup on the RPi first. \u00a0These are Webmin<\/a> and Smokeping<\/a>. \u00a0Having Webmin<\/a> and Smokeping<\/a> will allow us to troubleshoot much easier if there are issues later on. \u00a0We’ll need to install them since they\u00a0don’t come installed by default, at least with the current Raspian image. \u00a0It’s assumed that you have the Raspian OS installed with camera and SSH support enabled, along with XRDP. \u00a0We’ll be running the RPi headless, so these will be a requirement. \u00a0If you haven’t or that doesn’t make sense, please refer to my earlier post<\/a> for more\u00a0details.<\/p>\n

    Installing Webmin isn’t too much trouble. \u00a0These command<\/a> from a headless SSH connection should get you through the setup. \u00a0Once that is done, now you’re ready to view the health and operation of your RPi through a web interface,\u00a0https:\/\/<Your_RPi_IP_Address_Here>:10000\/<\/em><\/p>\n

    The Smokeping setup is fairly\u00a0straightforward. \u00a0Here is a post<\/a> about the setup and config, thank you Bernhard<\/a> and MyHomeBroadband.\u00a0 When that is all done, you can access the stats with your web browser,\u00a0http:\/\/<Your_RPi_IP_Address_Here>\/cgi-bin\/smokeping.cgi<\/em><\/p>\n

    Now that the RPi is ready, lets look at the hardware it will connect to and control.<\/p>\n

    Thermostats range in price and complexity. \u00a0However, the basic operation remains the same on all thermostats. \u00a0They change the state of an\u00a0electrical circuit when a user selected temperature is met or exceeded. \u00a0With hysteresis, they delay state changes from occurring too quickly, this protects the controlled hardware from damage due to cycling on and off rapidly.<\/p>\n

    Thermostats come in 2 flavors when connecting to circuits, low voltage and mains. \u00a0Since the RPi would be cooked if connected to mains, we’ll stick with the low voltage circuit variety.<\/p>\n

    The thermostat will be an input device to the RPi, meaning it will send data in to the RPi to tell it one thing or another. \u00a0The signal is binary, either on or off. \u00a0This means all we need the RPi to check is the HIGH or LOW state of a GPIO pin. \u00a0Find the relay control port on your thermostat, please refer to the documentation of your specific model. \u00a0I’ll be using a Honeywell\u00a0RTHL2310B<\/a>. \u00a0This model has a terminal block on the back of the unit that can connect to wiring. \u00a0The manufacturers instructions have details on how to connect the wires, but it’s not clear what port is the actual one to use for the RPi. \u00a0So I used a multimeter and found these for each of the operating modes.<\/span><\/p>\n

    \"ThermostatWiring\"<\/a><\/p>\n

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    Connecting these ports to the RPi isn’t as cumbersome<\/a>\u00a0as you might think<\/a>. \u00a0This post<\/a> on Make shows you some of the basics. \u00a0I’m using the older RPi board, so check your pinout for the newer RPi here<\/a>. \u00a0Either way, be sure to connect a 100 ohm resister between ground on the RPI and the thermostat. \u00a0Doing this will prevent potential problems if something shorts. \u00a0Now onto the output device.<\/p>\n

    Since the 5 volts coming from the RPi may not be what your furnace, pump, or fan is expecting, we’ll need to match the output with what the thermostat provides. \u00a0My thermostat closes a circuit when a set mode is operating,\u00a0just like it flipping a switch. \u00a0So, I’ll need to change my HIGH 5 volt output to a closed circuit. \u00a0This is easy to do with a\u00a05 volt relay module, I happen to have one from SainSmart<\/a> that was used for another project. \u00a0This board will be able to handle a 1000 watt heater, nice.<\/p>\n

    Controlling the relay module couldn’t be simpler. \u00a0All I have to do to get it to trigger is connect 5 volts VCC,\u00a0ground, and output a HIGH on one of the connected GPIO pins to the relay module. \u00a0Click, it’s on. \u00a0Now that the hardware is all good, let’s delve into the software\u00a0that will work with the devices.<\/p>\n

    The RPi has to monitor GPIO pins connected to the thermostat. \u00a0Based the state of each INPUT pin, it has to set the pin state on the GPIO OUTPUT pins\u00a0that control the relay boards connected to the\u00a0heater or\u00a0cooling fans.\u00a0 Basically, it’s going to match the INPUT to the OUTPUT.\u00a0 Although this will be happening behind the scenes, I would like to have some interface.<\/p>\n

    Here is where WebIOPi<\/a> comes into play.
    \n