Atmel AVR2016 Manual do Utilizador descarregar pdf (Página 5)

Figure 7: An USB-stick with IEEE 802.15.4 func-

tionality by Atmel

Figure 8: Node for message ferries

Figure 11 shows a graph of the voltages and currents in the

system. On the left side of the graph the sun is shining and

the harvested energy exceeds the needed energy. Therefore,

the battery is charged. Since the battery is almost full, the

charging process is interrupted frequently as the battery

voltage reaches the upper threshold. On the right side of the

graph it gets more cloudy. The amount of harvested energy

is now below the consumed energy, and the diﬀerence is

discharged from the battery. Around 850 seconds the battery

is charged again for a short period, but does not reach the

upper threshold.

The following table shows the energy consumption of the

main components. The PMMs MCU consumes roughly

13mW, but most energy is used by the XBee radio - more

than 450mW for constant operation. But we assume a rea-

-100

-90

-80

-70

-60

-50

0 50 100 150 200 250 300

RSSI [dBm]

Distance [m]

802.11a measurement 1

802.11a measurement 2

802.15.4 measurement 1

802.15.4 measurement 2

Figure 9: Distance-vs-RSSI from 802.11a and

802.15.4 radios

Figure 10: Evaluation setup

5000

10000

15000

20000

700 750 800 850 900

200

400

600

800

1000

1200

1400

Voltage (mV)

Current (mA)

Time (s)

Battery voltage

Current into DTN node

PV panel voltage

PV panel current

Figure 11: Voltages and Currents during charging

and discharging of the battery

1 2 3 4 5 6

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