Raspberry Pi Home Automation

This project began last year as a fun freshman design project at Drexel University, that continued into the summer on my own time. It has a ways to go, but basic functionality is proven.

Currently looking for help with debugging/testing. Also would appreciate help from any web developers or especially Javascript developers to improve UI and backend and also to add better task scheduling functionality.

The software design is based around a JSON file. This file allows changes to the hardware devices that are attached to the Pi to be easily updated. The software renders the GUI and initializes GPIO pin on the Pi based on this file. Below is a sample of the instruction manual that was written last spring. 

Adding Entries to device.json

In the main directory of this project is a file called “device.json”. When a client connects to the Node.js server, the server parses this file into a Javascript object, and packages this information into websocket data to send to the client. The entire system is based on the information contained in this file. The HTML control.html file does not contain any device specific information, it is simply a skeleton structure that allows the client-side javascript (contained in the /js/control.js file) to parse the data sent over websockets, and draw the page using JavaScript. This makes it relatively easy to add and remove devices from the Pi. By simply editing this file the whole interface is redrawn to accommodate those changes.

{

"pin" : 2,

"state" : "out",

"name" : "Alarm",

"id" : "buzzer"

},

{

"pin" : 27,

"state" : "in",

"name" : "Button",

"id" : "button",

"highmsg" : "Button pressed",

"lowmsg" : "No change..."

},

These are two examples of an object found in the device.js file. All objects must contain a “pin” key matched with an integer value. Pin corresponds to the GPIO pin on the Pi that the device is connected to, should be an integer. Note that there are two numbering systems used to refer to Rpi GPIO pins. The Pi has 40 pins, while referencing the relative position of pins, the board is always oriented so that the pin header is in the top right of the board. One numbering method numbers each pin from 1-40, starting the with top left pin as pin 1 (THIS IS NOT THE SYSTEM USED BY DEVICE.JSON). The numbering method used by the device.json file uses an arbitrary numbering scheme that is dictated by the processor design and follows no logical order on the pin header. Use the image below to determine the pin that your device is connected to. Use the integer that is prefixed with “GPIO”.

The first JSON entry above is an input object. For each output device connected the object must contain these fields: pin, state, name, id.

• pin is the GPIO pin that the device is attached to, this pin can either be high (3.3V) or low (0V aka ground)

• state is either “in” or “out”, we are discussing output device here so this should be “out”

• name is the string that will be displayed on the site interface. It can be anything but should be relatively short (so the page layout is not negatively impacted) and unique

• id must also be unique. This should be very short, less than 6 characters, and descriptive of the device that is connected. This value will be used in the schedling interface to refer to the devices that will change state on a certain date.

The second object above is an input object. Output objects contain the same four keys of the input, however they add two more keys: highmsg and lowmsg

• state is “in”

• highmsg should have a string value that will be displayed when the state of the input pin is high.

• lowmsg should have a string value that will be displayed when the state of the input pin is low.

The syntax of these objects is called JSON, aka JavaScript Object Notation. This syntax is very picky. If it is incorrect your object will not behave properly. Use http://jsonlint.com/ to check your JSON syntax before uploading. And check out W3 schools http://www.w3schools.com/json/ for more information on JSON.

Physically attaching a device to the Pi

1. What kind of device do you want to attach? It could either be an input (i.e. a sensor, or something that will take measurements of the surrounding environment) or and output (i.e. something that interacts with the surrounding environment, like an led or buzzer, or relay).

2. The device's power requirements are an important consideration. The raspberry pi can only supply so much power. If too much power is drawn by an output device, your system could experience sporadic behaviors (especially “brownouts” where too much power is drawn and the system shuts down for a fraction of a second, appearing to spontaneously reboot). Find out the power requirements of your device. If the device has 3 wires the wires will be attached to power(+5V or +3.3V), Ground (0V), and GPIO. If there are two wires (such as an LED) the device could possibly be driven directly from the GPIO but not without a series resistor to limit current. Check the device's datasheets to see which pin/wire corresponds to what. If your 3-wire device is a 5V device it can likely be powered directly from the 5V rail on the Pi, just plug the +5V (aka VCC) pin into the 5V pin on the Pi's header. The 3.3V header is limited to a total current draw (for all devices) of 50 mA. Do not exceed this. You may have to use external power for 3.3V devices.

3. The GPIO pins can supply 3.3 volts and a MAX of 16 milliamps each. However, in my opinion, you should not attempt to draw anywhere close to 16 mA from a GPIO pins. For more information on powering devices from the Pi see: (http://raspberrypi.stackexchange.com/questions/9298/what-is-the-maximum-current-the-gpio-pins-can-output)

4. Make sure that the power supply for the Pi (the wall socket with a micro-usb cable) can supply atleast 1.2 amps and 5 volts. Better yet play it safe and get a 2 amp 5 volt charger, most modern phones (including the iPhone) ships chargers capable of supplying this amount of power.

5. If you want to connect an LED, find an online resistor calculator, or use pen, paper and Ohm's law (Voltage = Amperage*Resistance), to calculate the appropriate resistance for the LED. Keep in mind the 16 mA limit, and how many other devices will be connected.

6. For 5 volt, 3-wire devices (input or output), connected ground to ground, +5V to +5V, and signal(input or output) to the GPIO pin (as recorded in device.json). Keep in mind that if your 5V device draw more than 100mA (or so) you may need to build an external voltage regulator, see step 8. Note that the power limit for 5V devices is limited by the amount of power available over the USB supply into the Pi, there is allot more leeway around 5V devices than there is for 3.3V devices.

7. For 3.3V 3-wire devices, if the power requirement fit within 50mA for ALL 3.3V devices, connect the +3.3V to +3.3V, ground to ground, and signal to the GPIO pin (as recorded in device.json).

8. If 3.3V device draws more than 50mA, get a breadboard (or protoboard) and put together a simple 3.3V regulator circuit with a few dollars worth or parts. Look online for instructions on how to do this. When complete plug the +3.3V power pin of the device into the +3.3V output from the power regulator on the external circuit. (this can also apply to 5V, just get a 5V regulator instead).

Systems Diagram