video-delay

A digital video input delay meter built on an FPGA

Overview

This project uses a custom photodiode sensor circuit and a DVI chip on a PMOD expansion board from 1BitSquared to implement a digital video input delay meter on a Digilent Nexys A7-100T FPGA development board. To within a margin of error of 0.1ms, the design aims to measure the time delay from the moment a pixel's data is sent to the DVI output to the moment it lights up the corresponding pixel on a TV or monitor. The video signal is driven by the 24bpp version of the DVI PMOD running in DDR mode, generating 720p at 60Hz.

For more details, watch the video on YouTube and check out the write-up on hackaday.io.

Running the project

To run this project, you'll need Vivado 2022.1 (or later) installed with its binaries available on your path. From the top level of this repository, run:

vivado -source init.tcl

This will start Vivado and create a subdirectory named video-delay with the project initialized in it. You can run synthesis, implementation and bitstream generation from within Vivado to try out the project on your matching hardware.

With a little effort, it should be very possible to port this project to other Digilent boards, such as the Basys 3. You would need to adjust constraints to account for different pinouts and different resources like LEDs and seven segements displays. Low-to-mid cost FPGA development boards from other vendors should also be plenty capable of running a ported version of this project. The PMOD pinouts and the clocking requirements are probably the biggest technical constraints. For relaxed clocking, you could certainly run a slower video signal, such as 480p. You could also drive an easier DVI PMOD, such as the 4bpp version of the same PMOD from 1BitSquared.

Branches

This repository is organized into branches for each of the development steps outlined in the video:

1. Sensor
   • Read data from the custom photodiode circuit and light up the development board's LEDs
2. DVI
   • Output a basic 720p 60Hz signal from the DVI chip that displays a color gradient
3. Sevens
   • Wire up user interface components of buttons and seven segment displays
4. Patterns
   • Create a user interface to control the pattern of pixels sent out by the DVI chip
5. Timer
   • Implement a timer to control the DVI output, measure a TV or monitor's response, and show the measured results on the seven segment displays