Talking to Computer Projectors

Over the last 6 years I’ve used a lot of computer projectors. Some projectors were a little brighter or had better contrast, some more acurately reproduced colours, and some were a lot smaller and portable than the rest. They all also provided different options for attaching a video source: VGA, Composite, DVI, Component, HDMI. However, I’m not going to talk about all that today. What I’m going to talk about are the projectors which also had a serial or USB connection to the the attached computer.

At first I didn’t get the point of a serial or USB connection to a projector. What would you use that for? Then I built a media computer (MythTV) connected to a projector, and realized than unless I wanted to manually turn the projector on and off, or use a learning remote, I needed a way for the computer to control the projector. Fortunately, my projector had a serial port which allowed 2 way communication with an attached computer: on, off, aspect ratio, etc. Cool.

However, most of the projectors I’ve used since then, if they had any data port at all, had a USB port instead. However, each projector used that USB port differently, supporting no more than 2 of the following features in any one case:

  • serial-over-USB used with a custom program to make the remote control work the computer
  • HID-over-USB which makes the remote control appear as a mouse and keyboard
  • USB mass storage which makes the projector look like a thumb drive which contains other drivers or programs for the projector
  • Video-over-USB which allows the projector to show video via USB instead of VGA

These are all great individually, but why not support all of them. With the processors and chipsets available today, and that much of the firmware is probably shared between the projectors made by the same manufacturer (lowering implementation costs), why can’t all of these features be available via one USB 2.0 cable?

  • serial-over-USB for controling the features of the projector and switching it on and off
  • HID-over-USB to make the projector remote control appear as a mouse and keyboard
  • Optional Video-over-USB (which sadly doesn’t seem to be entirely standardized yet)
  • Audio-over-USB so any speaker built into the projector doesn’t need extra audio cables
  • USB mass storage which makes the projector look like a thumb drive containing manuals, drives, and such
  • Even Ethernet-over-USB might be useful for providing a sink for streamed video from other computers on the network

All that in one package would be a very good use of the USB port on the back of a projector. And since most of these uses of USB are standardized, would work on just about any operating system out there.

By behanw

Behan Webster is an Embedded Systems Programmer with 25 years experience; his experience spans deeply embedded, through to large embedded systems (DSPs to mobile through servers to 5-9's telephone switches). He's been active in open source for almost as long. When he's not in front of a computer, he spends his time SCUBA diving, kayaking or building things.