A recent project was delivered to me with a problem with its LCD screen. In the process of testing it I wanted to generate a composite video signal. After looking at some ideas involving Arduino and resistor dividers I came across some examples of raspberry Pi testcards, specifically RPI - ATV
I had an original Pi model B which has an RCA socket with composite out so that was ideal for my task.
To get the testcard to work I downloaded a suitable picture and added my text to it. I then installed the python script into the /home/pi/atv folder and added my image and a dummy sound file into the /home/pi/atv/images and /home/pi/atv/sounds folders.
I tweaked the python script not to use the internal generator and also to load the first image.
#don't always start with internal picture internalPicture = false loadimage("1")
To add the cron job I ran the following which prompted me to pick and editor to edit the file.
sudo crontab -e
I added in my task to run on reboot.
@reboot python /home/pi/atv/atv3.py
For testing I plugged in a phono cable from the pi to my TV and booted it up using a USB battery box.