Virtual Laptop Display over Audio Proposal
From Catholicpenguin
Contents |
Overview
This device would capture RGB analog data from the monitor connector of graphics cards, store it in a frame buffer, then send a lower quality version out as audio data in a manner similar to SSTV to an application program on the machine.
Problem
When running headless servers, the situation often comes up where a machine does not respond over the network. When this occurs, the only solutions are either to remove the machine, or bring a monitor to attach to the machine in place. Often, neither of these are convenient.
Furthermore, often, the display quality needed to restore minimal functionality such that it can be further operated headless, or determine that the problem is non trivial is very minimal, such that full 60 FPS 24 bit color is not needed.
Solution
One very easy alternative would be if laptops could be used as RGB monitors. Then a technician would only need to bring a laptop to diagnose problems. The problem is most laptops do not offer RGB in. Therefore, this device uses a commonly available component, the PC audio port, to provide a low bitrate means of data transfer, allowing low frame rate low quality versions of what a monitor would see to be shown.
Furthermore, by using the audio port, even old laptops which do not have USB ports can be used. As the audio bandwidth is very limited, the display algorithms also require low CPU resources.
Technical Background
The component board would consist of an FPGA or other similarly powered logic device, running fast enough to decode the monitor data in realtime from the RGB pins. This data would then be compressed into JPEG streams, and sent over the audio line as data, running at approximately 115 KBPs rate.
Alternately, the images could be sent straight with no JPEG compression using AFSK SSTV encoded signals. As these signals are designed to be sent with limited bandwidth, a modification of sending two images at once, one using the higher frequency ranges, could speed up transfer. The downside would be potentially lower quality screen images on the PC.
