chwalters / potter-clock

Code for an ambient display that lets others know where you are.

Potter Clock

The Potter Clock is a simple ambient information display that provides a few bits of information about your location. If you are at home the display shows a blue light. If you are at school/work the light is red. If you are out-and-about then the light is green, and the intensity of the light increases as you near home.

The name "Potter Clock" was inspired by a magical artifact found in J.K Rowlings Harry Potter novels that provides similar information about the members of the Weasley family:

Mrs. Weasley glanced at the grandfather clock in the corner. Harry liked this clock. It was completely useless if you wanted to know the time, but otherwise very informative. It had nine golden hands, and each of them was engraved with one of the Weasley family’s names. There were no numerals around the face, but descriptions of where each family member might be. “Home,” “school,” and “work” were there, but there was also “traveling,” “lost,” “hospital,” “prison,” and, in the position where the number twelve would be on a normal clock, “mortal peril.”

Overview

The Potter Clock uses the Google Latitude web service and API in order to keep track of your location. The user updates the service with his/her location in whatever way they prefer (most likely with a GPS equipped mobile device). The display consists of an Arduino embedded device that controls the intensity of red, green, and blue LEDs based on commands given by a python script that periodically polls Latitude for the user's current location.

Use

To build your own Potter Clock, connect a red LED to analog output pin 9, a green LED to pin 10 and a blue LED to pin 11. Make sure to check the data sheets for your LEDs and use appropriately rated resistors for each. Use the Arduino IDE to upload the display_firmware.pde sketch to your Arduino.

Next, copy config.py.example to config.py and edit the values there. Set the home and work locations appropriately. You can find the latitude and longitude coordinates of a location by using Google Maps by right-clicking on the right location on the map and then clicking on the "What's here?" item on the context menu when it appears. The latitude and longitude will be in the search bar at the top of the results screen.

The client_id, and client_secret settings are strings supplied by the Google APIs Console. Go to that site and start a new API project. Make sure to set the type of the project to a native application by using urn:ietf:wg:oauth:2.0:oob and http://localhost for your redirect URLS.

Once you have config.py setup correctly generate the OAuth token by running python authenticate.py. The program will display a URL that you should copy and paste into your browser. You will then follow a few simple instructions to complete the OAuth authentication flow to retrieve a token that the application will use to authenticate in order to request your location. After that, you should have a file named latitude.dat in the Potter Clock directory.

Finally, run python potter_clock.py to start the "clock". For best results, run this command in screen so that it will continue to run should you log out.

Copyright 2011, Daniel Walker