Experiment with video on your Arduino!

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The Video Experimenter shield is an Arduino shield that lets you do all kinds of experiments with video.
  • Overlay text and graphics onto a video signal from a camera, DVR, DVD player, VCR or any other source of composite video.
  • Capture low-res video image frames for display or video processing. Give your Arduino the gift of sight!
  • Perform object detection for computer vision projects.
  • Decode NTSC closed captioning or XDS (extended data services) data embedded in television broadcasts.
  • Works with NTSC (North America) or PAL (rest of the world) television standards.
  • Uses digital pins 2, 6, 7, 8, and optionally 9. Uses analog pin 2.
All of these capabilities are demonstrated on the projects page.

How does it work?

The Video Experimenter uses an LM1881 video sync separator to detect the timing of the vertical and horizontal sync in a composite video signal. An enhanced version of the TVout library (available below) uses this sync timing information to overlay content onto the video signal. The ATmega328 microcontroller on the Arduino includes an analog comparator that can be used to detect the brightness of the video signal at any given point in time. Using this brightness information, low-res monochrome image capture into the TVout frame buffer is possible. The ability to capture image information in memory lets you implement simple computer vision experiments.

 

It's important to note that this shield will not work on the Arduino Mega. Read this for more information (it's not my fault!). The Video Experimenter will work on the Seeeduino Mega with some jumper wires. Read this for more information.

Board Features

A removable jumper allows you to control the source of the video sync signal. Typically you use the video input as the source of the video synchronization signal. But you can also use the TVout library without an input signal by generating the sync signal on digital pin 9 (this is the normal way TVout works).

 

A small switch lets you control whether the original input video signal is included in the output. Here's how these settings affect the output:

 

output select=overlay output select=sync only
sync select=
video input		 contents of TVout buffer overlayed onto input signal only contents TVout buffer displayed
sync select=
D9		 invalid setting contents of TVout buffer displayed (no video input present)
A potentiometer with a long shaft lets you easily adjust the analog threshold voltage used by the Arduino analog comparator. This allows you to adjust the brightness threshold value when capturing video frames.
The small potentiometer R4 is used to adjust the RSET value for the LM1881 sync separator chip. Normally, keep this at its lowest setting, but if you experience vertical jumpiness, you can increase it a bit. This adjustment is also useful for capturing closed captioning data from a broadcast.
All of the outputs of the LM1881 chip are broken out for easy access (burst, odd/even, vertical sync, horizontal sync). You can also access the video output signal on pin "output" or feed in a video input on the "input" pin (for example, if you have a small CMOS camera with wires instead of an RCA plug).

Enhanced TVout Library

The Video Experimenter requires using an enhanced version of the very useful TVout library. The enhancements allow the capture of video signal information in the TVout frame buffer so that primitive frame capture can be accomplished. The enhancements also facilitate the retrieval of embedded data streams from broadcasts.

 

Download the enhanced TVout library here

 

API summary:

 

capture() : captures a monochrome video frame in the frame buffer's memory. Stops display of frame after capture to allow processing of the data if required (for example in computer vision projects).
resume() : resumes display of the TVout frame buffer after performing a capture.
setDataCapture(int line, int dataCaptureStart, char *databuf) :

 

Arduino sketches that use the enhanced TVout library with the Video Experimenter shield also must perform some initialization of the ATmega registers. In the project examples you will find methods like initOverlay() and initInputProcessing() to enable certain features of the chip. These are not included in the library but the project examples show you how they are used. All Video Experimenter projects also have an interrupt service routine (ISR) for the input capture on pin 2. This is required, but not included in the library because it may vary from experiment to experiment.