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ABSTRACT
We designed and created a semi-wireless keyboard, audio, video and mouse (KAVM) switch. The KAVM switch allows a centralized Base Station to interface with Remote Stations connected to individual computers. Although we were not able to transmit all of our data wirelessly, the design allows for easy integration with wireless digital transceivers.
The device uses a quasi-TCP/IP protocol to transmit control data. The keyboard and mouse data are constantly sent from the Base Station to the currently enabled Remote Station. The audio and video are transmitted from the enabled Remote Station back to the Base Station.
The Base Station is typically connected to a television, a stereo system, a keyboard and a mouse. The Remote Stations are typically connected to a computer’s video and audio outputs and to the keyboard and mouse inputs.
Although our designs worked, there are still improvements that can be made by incorporating a better video encoding chip, using pseudo-random numbers for Remote Station identification, and implementing a wireless data routing network.
The final cost of implementation was higher than we expected. There are many ways the cost of production could be reduced and are discussed in the conclusion.
1. INTRODUCTION
We designed and created a semi-wireless keyboard, audio, video and mouse (KAVM) switch. The KAVM switch allows a centralized Base Station to interface with Remote Stations connected to individual computers. Although we were not able to transmit all of our data wirelessly because of time constraints, the design allows for easy integration with wireless digital transceivers. The device uses a quasi-TCP/IP protocol to transmit control data. The keyboard and mouse data are constantly sent from the Base Station to the currently enabled Remote Station. The audio and video are transmitted from the enabled Remote Station back to the Base Station. The Base Station is typically connected to a television, a stereo system, a keyboard and a mouse. The Remote Stations are typically connected to a computer’s video out, audio out, keyboard in and mouse in.
1.1 Purpose
The purpose of this project was to use our knowledge of communications, signal-processing, and digital system design, to engineer a product that would allow us to use our computers from a remote location. Since we both own keyboard, video, and mouse (KVM) switches, we spent some time thinking of things to improve upon.
We decided that we wanted our design to improve upon commercial products by buffering the video input. The VGA signals were sent out so a monitor can still be attached to the Remote Station’s computer. By providing multiple video output formats, we would improve the product’s usability. We would also eliminate long wire connections via wireless technology.
Although most commercial KVM switches incorporate function keys that allow switching between the inputs via the keyboard, this usually implements a time delay between hitting the function keys and when the computer receives the input. We wanted our product to have as little latency as possible.
1.2 Specifications
The KAVM switch needs to transmit and receive data with minimal delay. We set an initial upper bound for the transmission delay based on the number of words per minute a skilled person can type. Based on data from “The Guinness Book of World Records” [1], the fastest typing speed is 212 wpm. We assumed the average number of characters per word to be five, yielding 142 bps. Using this estimate, Equation 1.1 demonstrates that the KAVM switch needs to transmit around 300 bps, requiring a latency of less than four milliseconds. Minimizing this latency is important so that data does not get “visually” lost in transmission.
BPS [b/s] = WPM [w/m]  5 [c/w]  8 [b/c] ÷ 60 [m/s] (1.1)
The switch also needs to transmit video at a fast enough rate so there is no flickering. Estimating that we should be able to transmit VGA at a resolution of 1024 horizontal by 768 vertical and a vertical frequency of 60 Hz, Equation 1.1 tells us the needed data rate is more than 1,132,462,080 bits per second for true color. If this data transmission were done with an analog channel, we would need to send 5 signals each having a bandwidth of about 5 MHz. If we were to send only the composite video signal, however, we would have a reduced image quality and only need one transceiver with a bandwidth of roughly 5 MHz.
1.3 Subprojects
The design was broken into many modules, which each perform specific tasks. Diagrams 1.3.1 and 1.3.2 show block diagrams of the Base Station and Remote Station respectively. The internal blocks are independent modules that were designed, except for the LCD, which was borrowed from the ECE Parts Shop. Notice that the Base Station does not receive the video signals since these signals are controlled in the Router Module. Also, note that the Router is not shown because the Router Module is its only component.