Results of the Design
The wireless keyboard we constructed can successfully transmit keys to the keyboard. However, there are several issues in its performance. Its reaction speed is slightly slower than a normal keyboard. In addition, it occasionally drops a key or inserts a duplicate key. Overall, I believe that the transmission accuracy would need to be improved slightly before it could be used. This could be accomplished by tuning the baud rate and preamble length more finely, implementing an error correcting code, or combining multiple codes from the keyboard so that they use a single preamble. The more significant issue with using our keyboard is that the computer which we tested it on would not boot properly with the keyboard attached. This means that a normal keyboard must be attached to the computer before turning it on, and then replaced with ours. We had difficulty trouble shooting this problem because the oscilloscope could not lock on to the commands sent by the computer to the keyboard. Therefore we couldn’t see the signals and see what exactly we were doing wrong. We were unable to locate the problem within the time constraints of this project.
The other problem which can cause our keyboard to fail is interference with other hardware transmitting at the same frequency. This causes both our keyboard and the other hardware (everyone in the class working with RF uses the same frequency) to have trouble. The decoding scheme used by the receiver will keep most of this interference from being passed on to the computer, but the interference will prevent our signal from being transmitted as well.
This system is no more dangerous than a keyboard, or a cell phone. People might get carpal tunnel syndrome from using our keyboard (like other keyboard). In addition, some studies might show that exposure to radio waves slightly increases the risk of cancer. However, the power output of the circuit is quite low, so the dangers are not particularly excessive.