An often neglected
feature of the Raspberry Pi is that it actually has two types of
video output. The high quality, high resolution HDMI output and the
yellow RCA jack that outputs composite video at a much lower quality.
Miniature displays are readily available for this composite format, and are
often used for things like CCTV security and pocket TVs.
In this tutorial, you
will learn how to attach a miniature display to your Raspberry Pi and
to adjust the Pi's settings to reduce the resolution sufficiently to
read the screen.
To use a mini PAL / NTSC display, you will need
the following parts.
- A Raspberry Pi
- A PAL / NTSC Mini display, such as Adafruit products 910, 911, 913 or 947
- RCA Coupler Male to Male
- Female DC Power adaptor (unless your display has a DC barrel socket)
- 12V 1A power supply (unless included with the display)
- Raspberry Pi Console lead or SSH access to your Pi
Even the smallest of these displays will use
enough power to warrant its own power adapter, especially as they
generally do not use the 5V that the raspberry Pi uses. Often, they
are designed to operate at 12V but will be happy at a range of
Check when you buy the display, what voltage it
operates from. For some displays, a power adaptor will be included.
As an example, in this tutorial, we will use the Adafruit 3.5 inch display.
This display actually comes with two inputs (AV1 and AV2), I
simply cut one of them off, to neaten up the leads. You do not have
to do this, and you can use either lead when connecting to the Pi. Most only have one AV connection.
The unit comes in two parts, a control PCB and the
display itself. They are quite delicate, especially the plastic
ribbon that connects the two together, so handle with care.
I glued the control board to the back of
the display, to make a single unit. If you decide to do this, just
remember that if you need to separate them again, there is a good
chance of breaking it.
The unit has a black and a red lead to supply the
power. This can be between 6 and 12V. To make it possible to connect
the bare leads to a power supply with a standard 2.1mm DC power plug,
I used a Female DC power adapter. You can just pop the leads into the
screw terminals, tighten them up and then use a regular DC power
supply. Be very careful that the red lead goes to the terminal marked
with a +.
The display I used has RCA sockets, as they are
intended to be connected to a video source such as a camera or in
this case the Raspberry Pi via a cable. As you are probably going to
have the display right next to the Pi, you do not really need a
cable, and an RCA Male to Male adapter will allow you to connect it
to the yellow socket on the Pi.
Turn on the power to the display and then power up your Pi. You should see the Pi start to boot up on the display. You will notice that the writing is pretty tiny and a little fuzzy.
We need to change the screen resolution so that we can see what is going on.
The native resolution of the display I used, is just 320 x 240 pixels.
To adjust the resolution, you need to edit the file /boot/config.txt
You can edit config.txt on the Pi itself by running sudo nano /boot/config.txt or you can safely shut down the Pi, remove the SD card and put it a computer, the config.txt file is on the 60MB partion that should appear when you insert the card
If you are trying to edit it directly on the Pi, this may present a bit of a problem, if the whole reason for changing the screen resolution is to be able to read the text. You can either attempt to edit the file using the mini display, or connect remotely to your Raspberry Pi from another computer using SSH or, as I did here, using a console cable.
To edit the file, issue the command
sudo nano /boot/config.txt
sudo nano /boot/config.txt
You need to remove the # from the start of each of
the two lines, to make the setting active and then change the two
values, so that the two lines are like this:
Save and exit the editor by pressing CTRL-x then
Restart the Pi and you should find that all the
text is bigger and clearer.
Now, you will have noticed that there is quite a
wide border around the visible area of the screen. Since we have so
little screen to play with, we really need to expand this as much as
Fortunately, there is another set of settings that
we can change to reduce this as much as possible.
Edit /boot/config.txt again and this time, remove
the # from the four lines that start with #overscan.
Change the numbers to be negative (makes the
screen wider and taller). I found changing them to the figures shown
below, used most of the screen vertically, however I could not get
the screen any wider after about -25.
You will find that a bit of trial and error will
be required to get the right settings for your display.
With the overscan adjusted, the resulting screen
is now looking pretty good.
Starting a Terminal session, the text is now quite
easy to read.
These changes to the settings will also affect (for the worse) the display if you connect up using the HDMI adaptor. To reverse the changes, just add a # character in front of each of the 6 lines that you changed earlier.