Hand Hygiene

This test explored receiving and sending power variations between and within motes for one specific configuration. The purpose was to determine if, when a particular power or RSSI level was chosen in practice, that level was reliable for other motes and how much variation there might be for a given arrangement. One mote was used as a reference. Fourteen other motes, including 4 in badges, 5 in pucks, and 5 unencased, were used as test subjects.

One mote was fixed in place and each of other motes were placed, one at a time, at the same fixed distance and orientation from the first mote. Both motes were at the same height (46″ above ground) and 24″ between from each other. Both motes were placed with the USB facing upwards and the circuit boards facing each other (battery packs facing away).

The OnePowerBlinkRadio program was loaded on both motes, with the reference mote being identified as mote #1 and the other as mote #2. This program caused each mote to broadcast a signal at power level 5 on channel 11. Each mote also listens for broadcasts and when it hears a transmission, it report the number of the transmitting mote and the RSSI value of the reception. This report broadcast is picked up by the serialListen program and logged to a file. Each mote was tested against the fixed mote for one trial, with approximately 120 communications each way.

The results suggest that motes receiving identical signals report similar RSSI values (42.87, 40.06, 45, 46.48, 39.71, 39.80, 36.2, 36.47, 34.05, 41.05, 44.96, 41.61, 43.07, 40.93) with an average response of 40.9 and a standard deviation of 3.7. Within a trial, the motes were remarkably consistent with a standard deviation of just 0.64.

Reports from the broadcasts heard by the reference mote were similar. These were pooled with an average value of 39.43 and a standard deviation of 4.36.

Reports from the motes in the pucks were notably different from the others. It appears that most could receive signals normally, but many of their broadcasts were not heard by the receiver. However, one had its batteries replaced just before the experiment and its results were normal. We’re double checking those values.

[from an earlier draft] Several guesses as to why this may be is that either the batteries were low or the plastic somehow interfered. Also, not only were these mathematical values different, the number of packets received by the receiver from the hockey pucks was quite a bit lower in 3/5 cases (one was down to around 20, from the expected 120). These results point us in the direction of more testing of the hockey puck style motes and their respective sensitivity.

Link to Data