Speed and Accuracy
We did not observe much latency or delays in the communication between the transmitter and the receiver. Although we're only transmitting at 1200bps, it's still very responsive. We could achieve a range of about 60 feet and still have the receiver acquire the signal. That is, as long as the planets are aligned just right, there's a full moon, and we ask really nicely. Transmission at 30 feet was much more reliable. A problem we were not able to debug was that sometimes the blinking speed gets reset for some reason, so a temporary visual change in frequency of the lights can easily be detected. It's rather rare once the states aren't transitioning, however. Besides that, everything works the way we wanted it to.
To avoid the RF interference from other lab groups in the room, we send a start byte before our data and a stop byte after it. This ensures we are decoding the correct data packet. We also check for parity and frame errors, as well as our data being an active-low one-hot decoding. So we had no trouble rejecting weird data that didnít belong to us. We also only transmit when the user desires a change in operating modes, so we don't cause much interference either.
With the large amount of voltage and power that we have to deal with in this project, especially within the power strip, safety is a critical factor in our design. In order to minimize the danger of any lethal electrical shock, we enclose all our high voltage AC circuit components in a grounded steel box. All connections are secured, and everything is properly insulated and sealed inside so that nothing is exposed. Only a small hole is drilled through the box for signal wires to come out so that the rest of the controls can be done outside of the box. In addition, we have a 15A circuit breaker between the wall plug and the relays. If anything were to short out, the breaker would trip, and excess current would be channeled through the earth ground.
Another safety concern for our project may be the possible health hazards of radio frequency that we will be transmitting. Studies have shown that exposure to very high intensity RF causes thermal effects that are harmful to humans. The harm is that it increases body temperature and heats biological tissues rapidly. However, experimental results show no evidence that low level RF radiation, which we will be using, poses any dangerous biological effects at all. We experience the same level of radio frequency in our every day life from cell phones already, so using radio as our means of communication to control the power strip should not be an issue.
We labeled all our buttons in a simple manner, so users can play around with
them and learn the different modes and speeds available. Our design should be
pretty user-friendly. Each light is individually controllable, they're all
controllable as a group, and the mode/speed buttons cycle through available
options. If the user hasn't connected anything to the outlets, he can
watch the LEDs on the receiver board to see what is happening.