I started with the integrated circuits, then moved to the
resistors, capacitors, and inductor, and finally finished with
the jacks and headers. It took me about two days to solder
by hand, working about two hours each day.
I would definitely recommend using a continuity
tester to make sure you haven’t bridged any pins. Oh, I
forgot to tell you ... you can prototype the video portion
of this board. I used a different encoder (AD725) with a
breadboard adapter and there are some minor changes to
the schematic. The completed shield can be seen in Figure
2 and the prototype in Figure 3. The prototype schematics
are available with the article downloads.
The NTSC standard is old. How old, you ask? I’ll give
you a hint: The first iteration of the standard was developed
during the same year as the attack on Pearl Harbor. So,
why is it difficult to implement on an FPGA?
Well, when the standard was first written, it was
designed for black and white televisions. Sometime later in
1953, the engineers added color. Since most people still
owned black and white televisions, the engineers had to
figure out how to integrate color information into the older
signal. They had to do this while simultaneously retaining
backwards compatibility. This makes the standard a bit
interesting. No, really!
If you read about the history and how the engineers
made it happen, it’s quite fascinating! Anyway, the color
information is stored by varying the amplitude and phase
of the color burst signal (actually 3.57545 MHz). That kind
of analog work doesn’t mesh well with FPGAs.
From the 10,000 foot view, an NTSC signal is made of
frames, fields, and lines. A frame is one complete picture
on the screen and a field is one half of a frame. Okay, I
know what you’re saying ... “huh?” The NTSC signal is
Figure 2. Completed NTSC shield.
Figure 4. NTSC raster scan (
Hackaday.io Project Page
OSH Park PCB Page
Analog Video 101
Television Safe Areas
Video Formats and Required
September/October 2018 71