Using Composit Video

[SerenityNetworks]

I'm able to work on my RPi using HDMI without any issues. (I'm using Wheezy.) I have both an old B&W 5" CRT monitor and a car backup digital display (http://www.amazon.com/Monitor-Support-R ... ref=sr_1_4). I know both displays work. I can plug in my camera-to-RCA cable and have instant video. However, when I plug in my RPi then I get nothing. Like the HDMI, I thought the composite video was to work without configuration.

I boot with the composite video cable plugged in and nothing in the HDMI port, and get no video output that I can detect. I boot &/or plug in the HDMI cable after boot, and have instant video.

How do I troubleshoot this, or better yet get the composite video to work at 480 x 272 resolution? I want to be using the car backup display as a small monitor.

Thanks in advance,
Andrew

[FTrevorGowen]

I'm able to work on my RPi using HDMI without any issues. (I'm using Wheezy.) I have both an old B&W 5" CRT monitor and a car backup digital display (http://www.amazon.com/Monitor-Support-R ... ref=sr_1_4). I know both displays work. I can plug in my camera-to-RCA cable and have instant video. However, when I plug in my RPi then I get nothing. Like the HDMI, I thought the composite video was to work without configuration.
I boot with the composite video cable plugged in and nothing in the HDMI port, and get no video output that I can detect. I boot &/or plug in the HDMI cable after boot, and have instant video.
How do I troubleshoot this, or better yet get the composite video to work at 480 x 272 resolution? I want to be using the car backup display as a small monitor.
Thanks in advance,
Andrew

How did you install the O.S. (Raspbian)? If you used NOOBS then that installer defaults to making HDMI "permanent"**.
Can you post the result of cat /boot/config.txt (if you're using Rapbian or if it exists for your O.S.)?
(It's quite likely that config.txt has "hdmi_force_hotplug=1" uncommented which means that the HDMI port is always in use rather than only if the "hotplug" signal is present.)
Trev.
** Making composite "permanent" instead is shown in this example:
http://www.cpmspectrepi.webspace.virgin ... ellow.html

[SerenityNetworks]

Thanks. I'll be able to follow up and take a look tonight when I get home. But yes, I used NOOBS.

Thanks again,
Andrew

[SerenityNetworks]

Thank you for your help.

I modified the config.txt file as below. The composite video is now working on the little 4" display, although the print is quite small. Would you mind proofing the config.txt file to see if I have it correct? Also, the little 480 x 272 display has a good 1/2 inch margin on either side of the graphics, with just a little margin at the top and bottom. How can I change the settings to eliminate the margin, or at least most of it? Would this be a combination of the overscan and framebuffer settings? If so, do you have any suggestions on the proper settings? (I experimented, but it was a failure.)

Thanks again,
Andrew

=================================================================
pi@raspberrypi ~ $ sudo cat /boot/config.txt
# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# for more options see http://elinux.org/RPi_config.txt

# NOOBS Auto-generated Settings:
#hdmi_force_hotplug=1
#config_hdmi_boost=4
overscan_left=24
overscan_right=24
overscan_top=16
overscan_bottom=16
disable_overscan=0

[FTrevorGowen]

Thank you for your help.
I modified the config.txt file as below. The composite video is now working on the little 4" display, although the print is quite small. Would you mind proofing the config.txt file to see if I have it correct? Also, the little 480 x 272 display has a good 1/2 inch margin on either side of the graphics, with just a little margin at the top and bottom. How can I change the settings to eliminate the margin, or at least most of it? Would this be a combination of the overscan and framebuffer settings? If so, do you have any suggestions on the proper settings? (I experimented, but it was a failure.)
Thanks again,
Andrew
...

AIUI, the composite video resolution is "fixed" at 720x576, but check http://elinux.org/RPi_config.txt to be sure. Use negative values of overscan (4 pixel steps) to, hopefully, eliminate the margin and set the framebuffer to match your 480 x 272 display to increase the "font size" in "command-line" mode (with such a low-res display I suspect the graphical desktop will be virtually unusable). FWIW, example settings etc. for a standard CRT TV are shown here:
http://www.cpmspectrepi.webspace.virgin ... Input_only
Trev.

[SerenityNetworks]

Thanks for the guidance. It's much appreciated. The command line font is readable, although if I can make it a bit larger then all the better. I tried the GUI for giggles and surprisingly it is usuable - quite tough to use, but it can be used.

My end goal project has me using the device headless over WiFi in the field (on battery). Having a command line display is my fallback if the wireless goes South. I don't see me ever really using the GUI except as a novelty.

Thanks again,
Andrew

[SerenityNetworks]

The following uncommented lines in the config.txt file result in a near perfect display on the little 4" screen.

framebuffer_width=480
framebuffer_height=385
sdtv_mode=2
overscan_left=0
overscan_right=-12
overscan_top=0
overscan_bottom=-16
disable_overscan=0

Surprisingly enough the GUI is quite readable and useful with the above settings. The only other tweak I made was to set the 'desktop preferences' do display in 12 point font instead of the default 10.

Thanks again,
Andrew