Overview
First thing’s first: What video standard should we use
as the basis for the shield? The standard that makes the
most sense is HDMI. After all, it’s purely digital and lends
itself to FPGAs (field-programmable gate arrays). However,
Embedded Micro has an HDMI shield and it would be silly
to reproduce their efforts.
How about VGA? It’s really not too tough to
implement the VGA standard on an FPGA, and most
monitors and televisions have a VGA input. Plus, VGA is a
tried and true project for FPGAs. I have a better idea! Let’s
go with an old friend: the ubiquitous NTSC standard.
You may recognize it as the yellow RCA jack
(composite video) or mini-DIN (S-video) on the back
of your television. NTSC is an old analog standard and
it’s certainly not the easiest to decipher or implement
on an FPGA, but almost every video input device in the
US includes it as an option. Come on, this will be fun!
(Disclaimer: This was extremely frustrating at times.)
Okay, how do we do it? Like I said before, the NTSC
standard is not simple to implement on an FPGA (more
on that to follow), but thankfully there are already devices
on the market that do a lot of the heavy lifting. The device
we’ll use is the Analog Devices AD723 RGB-to-NTSC/
PAL Encoder. This device accepts analog RGB and digital
synchronization signals as inputs and generates the
FPGAs for the Hobbyist:
If you have read my previous Nuts & Volts
articles in the FPGAs for the Hobbyist
series, you already know that I’m a big
fan of Embedded Micro’s Mojo V3 FPGA
Development Board. Embedded Micro offers
a handful of expansion shields for the Mojo
V3. However, at the time I wrote this article,
there was no video shield available. Well, I
don’t know about you, but that sounded like a
great project to me! So, let’s go on a journey
to design a video shield for the Mojo V3.
By Ryan Clarke
KJ6MSG @kj6msg
NTSC
Shield
September/October 2018 69
