Aug 31, 2014

Start messing around with Python: Raspberry Pi drive recorder with GPS logger

Previously I finished setting up Raspberry Pi, attaching required peripheral devices, testing those devices, installing required software packages and making backup. I think it's a good time to start writing some code for this project. When this coding is done the prototype looks like this.
click to enlarge
Live preview with current recording status and driving speed are displayed on PiTFT. The good thing is that this can record and preview at the same time. I didn't really have to display current speed on it, but I added it anyway because my wife always care about how fast I'm driving. Maybe I could subtract 10 or 20 from this speed to make her comfortable.
I'm going to explain what modules I created and how they work together.


For this project, I decided to go with modules below:

This module is basically responsible for 3 things.
  • It sets environmental variables used for gpsd and PiTFT.
  • It maps each tactile button and corresponding function.
  • Initialize Odyssey and start this camcorder application
In this way other modules don't have to deal with GPIO and can concentrate on dealing with their own process and logics. In fact, is the only module that imports RPi.GPIO.

This is the key part of this project. On its initialization, it initializes GPSController and PiCamController and stores those instances so it can manage them on user interaction. This provides interface to switch preview, recording and GPS logging. uses this interface.

Obviously this handles GPS device. On initialization it starts gpsd so we can receive data from GPS Breakout . It provides access to GPS data and when recording status is active it logs current location and speed data to designated file every five seconds.

While GPSController deals with GPS device, this deals with Raspberry PI Camera  and PiTFT . I started with having separate module for camera and PiTFT: and PiCamController. However camera and preview works closely together( e.g. share the same pythone-picamera instance) so I combined them in one module.

How they work together

GPSController and PiCamController both inherit threading.Thread so they create new threads for each of them. This way these 2 instances don't block each other and Odyssey can still have control over them.

I'm going to explain how each module works on later articles. Making live preview and recording work at the same time and overlaying current status on preview were some tricky. I'll spend some time explaining them, too.