Nov 3, 2014

Trying out picamera's overlay function: Raspberry Pi drive recorder with GPS logger

I introduced a new version of picamera and its new feature on last article. This new feature lets us add overlays to the preview. You'll never have to continuously capture image from camera and add some image or text to it before sending to display device as preview; just render preview with show_preview() and add as many layer as you wish to show some statistics, recording status, or anything you want.

Below are example of both implementations.

1. Capture image, add text to it, and send it to display device continuously

It was the only way to add modification to preview until picamera ver. 1.8 came out. Because this implementation shows preview by continuously updating image, frame rate can be lower as the image modification process gets slower; Slower the loop process, fewer the image capture.

2. Show preview on the bottom layer and add overlay to show text

This way, preview can be shown with show_preview() just like plain procedure without any modification. Text or additional image can be added as an overlay on top and this layer may be replaced with your desired frequency. As you probably figured out, the additional layer doesn't affect preview quality. The problem is that this preview output goes to default display device, /dev/fb0 while PiTFT is assigned to /dev/fb1. Therefore we need to copy /dev/fb0 output to /dev/fb1 with rpi-fbcp. Fbcp takes a snapshot of /dev/fb0, copies it to /dev/fb1 and waits 25ms before repeating. Snapshotting takes ~10ms and with a 25ms delay it gives roughly 1000/(10+25) = 28fps.


Despite the latency rpi-fbcp gives, the solution with overlay works better for me. I also like this in a point that we can separate preview and overlay implementation.
Now I'll be taking a break and wait till PiTFT HAT comes out.

Sep 6, 2014

What I've learned about MMAL and picamera: Raspberry Pi drive recorder with GPS logger

To interact with Raspberry PI Camera Board from Python, I chose a library called picamera. It provides us interface to control Raspberry Pi Camera without using raspistill, raspivid and/or raspiyuv utilities. Actually it provides even more features such as taking images and recording video at the same time, modifying options while recording, etc. I think this library is reliable because it is well maintained by its owner, waveform80, and is used in adafruit's sample project. While reading its code, I found it was very important to understand the concepts and basics of Multi-Media Abstraction Layer(MMAL) so I began reading MMAL's specification. This article covers what I've learned about MMAL and how picamera works with it.


First of all, Raspberry Pi has BCM2835 that has VideoCore IV inside. Ad I already mentioned, MMAL stands for Multi-Media Abstraction Layer and it provides lower level interface to multi-media components running on this VideoCore thing. Actually MMAL runs over OpenMAX so there is another layer below MMAL, but I decided to ignore it. As long as MMAL works fine as an abstraction layer and fulfil my requirement, I don't have to be aware of anything behind it.

Here is how MMAL works.
  1. Client creates MMAL component via API.
  2. When creation is done a context is returned to component.
  3. This context provides at least one input port and one output port. This number and format may vary depending on what this component represents. The format of input port must be set when component is created; The format of output port may be decided later and can be modified by client.
  4. Client and component send buffer headers to each other though input/output port to exchange data. Component can also exchange buffer headers with other connected component.
  5. There are two kinds of buffer header:
    • One contains meta data and pointer to actual data.
      Payload, the actual data to be exchanged, is not stored in buffer header so the memory can be allocated outside of MMAL.
    • The other one contains event data.
  6. These buffer headers are pooled and each of them gets recycled when it's no longer referenced.

How picamera works with MMAL

The good thing about MMAL is that MMAL components can be connected to each other so they can exchange buffer headers. This well designed library, picamera, creates and uses some different kinds of components effectively to work with Raspberry Pi Camera Board. My favorite thing is that it creates a splitter component that receives video output from camera component and splits this input to 4 output ports. This way we can capture image via video port while video recording is in progress.

Components created on initialization

When picamera is initialized, it creates components below:

Camera component

This is the most important one. Everything starts from here. This component provides 3 output ports:
  • preview
  • video
  • still
The other components I'm going to introduce receive data directly or indirectly from these output ports.

Preview component

Basically we have two components here.
One of these components' input port is connected to camera component's preview output. On initialization and when actual preview is not needed, null-sink component is connected. It is necessary because if we don't connect any component to the preview output provided by camera component, the camera doesn't measure exposure and captured images gradually fade to black. When start_preview() is called, it creates preview renderer component and replaces null-sink component with this preview component that actually shows preview.

Splitter component

Its input port is connected to the camera component's video output. It has 4 output ports and each output port works as a copy of camera component's video output. This way, we can record data from one of its output ports and capture image via another output port at the same time. Yes, capturing image via video port is faster and you might want to use it (camera.capture('foo.rgb', use_video_port=True)).

Other components

Some other kinds of components including encoder and renderer are created when necessary. Thanks to waveform80, A new version of picamera, ver. 1.8, was released today and it provides interface to create and manage MMAL renderer components. This must be really handy when you want to add overlay to your preview. I, for one, wanted to have this feature so badly that I asked @wafeform80 about release schedule, last night.
He was nice enough to respond to me with a sense of humor and he really released it!
I'm going to rewrite the live preview part and try its new features over this weekend.

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.

Jul 21, 2014

Make a copy of your SD card: Raspberry Pi drive recorder with GPS logger

With previous steps, we installed required hardware/software and finished basic configuration so we can now take photo, shoot video, output data to external touchscreen and fetch location data. Before writing some Python code to let those modules work together, I think we should take some time to make a copy of the disk we worked on. This way, even if you make a huge mistake in the near future and everything is messed up, you can install this saved disk image and start from where we are now. It's just like playing your favorite RPG. You don't wanna start from scratch, right?

Making a copy

Just like when we installed Raspbian OS to empty SD card, we use dd command to make a disk image. You insert your SD card to your iMac and hit `diskutil list` to see which disk we are going to use. Then execute `sudo dd if=/dev/disk1 of=Odyssey-Mk1_20140721.dmg`. You should change 'if(input file)' and 'of(output file)' value to suit your environment and preference. My 8GB SD card took 20-30 minutes to complete. It will be longer if you have SD card with larger space.


When you want to install the saved disk image, the process is almost the same as when we installed Raspbian to a fresh SD card. First you insert an SD card that you want to install this disk image to. Then unmount this just like the initial installation. Then `sudo dd if=Odyssey-Mk1_20140721.dmg of=/dev/disk1`. Again, you must set 'if ' and 'of' value to suit your environment.
It takes longer than making an OS image. In my case it took me more than 2 hours. You must be really patient.

My trick

If your SD card has larger space and you have chosen to 'Expand Filesystem' on the initial configuration, both steps take longer time to complete. So I make my 8GB SD card to be a master and make a copy of it. This way it doesn't have to copy each and every byte of 64GB. Then I install this to Micro SD card with larger volume. Right after this installation, this Micro SD card only utilizes 8GB of the entire space because I made a copy of 8GB SD card.
So I `sudo raspi-config` again and choose 'Expand Filesystem' to utilize all spaces left.

Jul 20, 2014

Setting up GPS module: Raspberry Pi drive recorder with GPS logger

Previously we attached PiTFT and finished touchscreen configuration. Now we are going to add GPS module to fetch location data.

For my project, I chose Adafruit's Ultimate GPS Breakout. I searched some GPS modules on the web and Adafruit's one have detailed official guide and many reference article by users. Spec. seemed good, too:

Freeing UART

2 ways of connection are introduced on the official guide:

The former seems easier and the guide recommends this way, but I chose the later one because I didn't want to use one of two USB ports. To do it some extra steps are required.

First you need to edit /boot/cmdline.txt

You need to remove those parts that include console=ttyAMA0 because we are going to use ttyAMA0 from now. I added rpitestmode=1 because other users' blog entries seem to include it.

Second you edit /etc/inittab

Then reboot and activate your change. This step is done.

Installing required packages

Before connecting GPS module, install required packages. It includes some interface that you can later use to interact with GPS data from python code.

Connecting GPS module

This time we use the cobbler cable I introduced in my previous article about PiTFT. It looks like the capture below.

As shown in the second capture, you should connect GPS module's VIN to Pi's 5v, GND to GND, RX to TXD and TX to RXD. Note that TX and RX are cross wired since module's input is Pi's output and vise versa.

Check and debug

You execute `sudo gpsd /dev/ttyAMA0 -F /var/run/gpsd.sock` and now gpsd is running. Check if you can properly read the receiving data by `cgps -s`. If it's working, the output is something like below.

In my case it didn't work at the first place and I had to go through debug process.
To add debug option to gpsd you add -D followed by a number that indicate debug level. e.g. `sudo gpsd /dev/ttyAMA0 -N -D3 -F /var/run/gpsd.sock`. I saw messages like below. It kept saying 'Satellite data no good (1 of 1).'

I couldn't really tell if the wiring connection has a problem or the GPS module is not receiving data. So I checked what's in /dev/ttyAMA0.

The GPS module was set by a window, soldering seemed O.K. and it looked like my GPS module was receiving some partial data. I couldn't really tell what to do so I posted to Adafruit's forum. As shown on the forum topic, they were kind and helped me well. Now my GPS module works perfect and I can receive consistent data.


I didn't know GPS module is so sensitive until I faced the problem. Now I have my external antenna attached. You can set this antenna on the roof of your car to receive better data. To do this you'll need:
Basically we installed all required packages and attached all modules we need. We are going to make a copy of OS before making any mistake and being forced to start all over again.

Jul 19, 2014

Setting up touchscreen: Raspberry Pi drive recorder with GPS logger

Since PiTFT itself is already setup in the last step, now I continue to setup touchscreen. This step is also documented on the official document so you should read though this first.

Basic setup

To start with, we make udev rule for the touchscreen.
Then remove and re-install touchscreen package. Then check if current setup went O.K. Now touchscreen should refer to eventN where N is number.


Before calibration process I installed some handy tools that were introduced on the document.


I installed mplayer for later preview use.
I downloaded video from and played it with the code below, which is exactly the same as documented.
Then I saw some scary message. I'll have to check this out later. I'm just going to add GPS module and see if it works.

Setting up PiTFT: Raspberry Pi drive recorder with GPS logger

Since we are done installing RaspiCam, now we are going to attach PiTFT and install required software. Before setting up PiTFT you should read through the complete document because it covers pretty much everything. What we need to do is to solder hardware and install some software packages.


When you open the PiTFT package you'll find extra 2x13 IDC socket for additional cobbler cable. PiFTF's female header covers Pi's all 26 GPIO header pins, but it actually uses 3 of them so it seems a good idea to connect cobbler cable to utilize the rest of 23 pins.
Cobbler breakout and cable package includes parts as shown below. You can stick the pins right to your breadboard so its really easy to add and test other modules like GPS and microphone amplifier module.

If you solder IDC socket, don't solder it on top of it. Do it on the reverse side.

And you make sure the white code, pin 1 indicator, goes right next to the female header.

When you solder female header and optional IDC socket, hardware part is done. Set the female header to your Pi's GPIO header pins.


Software part needs a bit more work than RaspiCam. You'll need to get 5 packages as described on the document:
And then use dpkg to install them. The install log is shown below. You need to reboot your Pi to activate this change.


After rebooting your Pi, you need to let your Pi install screen driver. Commands are below. This modprobe command lets you load kernel modules. In this case we load spi-bcm2708 and fbtft_device.
If it goes O.K., the desktop shows up.

From next boot, we want Pi to load those kernel modules automatically so we add some modifications to /etc/modules. The modules listed in /etc/modules are loaded on boot so we don't have to repeat the previous step to load them.
And add new file: /etc/modprobe.d/adafruit.conf. rotate value indicate the rotation angle while frequency tells how fast it should drive the display. If the display acts weird document suggests you to drop this frequency value to 16000000.
Reboot and add some calibration setting.
Add some setting to .profile for later convinience.
Then run `startx` and desktop will show up.

Display STDOUT on PiTFT

If you wish to output standard output to PITFT on boot, make some change to /boot/cmdline.txt like below.

Then hit some commands and PiTFT will display standard output.
When you want to turn it off you simply write 0 to /sys/class/gpio/gpio252/value.

We are going to setup and calibrate touchscreen, now.