T having a sampling frequency of two MHz plus a granularity on the respective existing measurements of 1.5 nA. The visible spikes are brought on by the TPS63031 DC/DC converter operating in power-saving mode as described in Section four.three.Figure 14. Current consumption in and duration of the active phase.In Figure 14, also the distinct states with the sensor node and their duration are visible. It takes about 48 ms for the CPU to grow to be active just after receiving the wake-up signal (i.e., external interrupt in the RTC), requesting the XBee to wake-up, as well as the XBee to be ready for operation (IS1 = 4.68 mA). For about 557 ms the ASN(x) is querying the attached Compound 48/80 Technical Information sensors and deriving particular self-diagnostic metrics (IS2 = 13.4 mA). This phase, nevertheless, takes the longest time and is partly triggered by a delay in between the XBee’s wake-up and the Zigbee network rejoin (cf. Section three.2.1). The transmission of data from the MCU for the XBee module via the USART interface (at 9600 baud) requires approximatelySensors 2021, 21,34 of289 ms (IS3 = 15.7 mA) when the actual transmission by way of Zigbee only takes about 19 ms (IS4 = 24.48 mA). Within the following 135 ms the XBee module waits for the message recipient to acknowledge the transmission and reports the corresponding return value back towards the MCU (IS5 = 14.27 mA). For the subsequent 94 ms, the ASN(x) finishes its processing of data and requests the XBee module to go back to sleep mode (IS6 = 13.4 mA). Overall, in the present demo case the ASN(x) spends about 1142 ms in among the active states and is place to the power-down state the rest on the time (IS7 = 36.7 ). The power consumed by the ASN(x) in a single 10 min interval may be the cumulative sum on the energy consumed in every state and equals:||S||Qnode,10min =i =( ISi tSi ) = 37.86 mAs 10.52 h(17)exactly where S would be the set of states with their respective length and existing consumption as presented above. In our setup, the sensor nodes had been powered by two Alkaline LR6 AA batteries (Qbat = 2600 mAh). Hence, the anticipated battery life is usually estimated as follows (a 10 min interval GNE-371 manufacturer equals 6 updates per hour): tbat = Qbat 2600 mAh = 1 h 41191 h 4.7 years Qnode,10min six 1h ten.52 h 6 (18)To confirm our estimation, we measured the power consumed by the ASN(x) utilizing the Joulescope for six h (again at a sampling frequency of two MHz) resulting in an typical energy consumption of 65.1 h per hour (= 10.85 h per 10 min) which equals an anticipated battery life of four.56 years. Subsequent, we analyzed the energy efficiency with the DC/DC converter employed on the ASN(x). As described in Section 4.3, its energy efficiency depends upon the input voltage level as well as the output present. With all the “supply voltage sweep with plot” instance script of our ETB (see https: //github.com/DoWiD-wsn/embedded_testbench/tree/master/source/examples), we analyzed the power efficiency on the TPS63031 by applying varying input voltages, measuring the input current and calculating the corresponding input energy pin . Thereby, voltages amongst 1.five and three.five V had been applied (in descending order) and 1000 measurements per voltage level with two ms between have already been taken. For the duration of the measurements, the ASN(x) was in an idling state (for the source code, see https://github.com/DoWiD-wsn/avr-based_sensor_ node/tree/diagnostics/source/006-idling). The mean typical current consumption at every level has then been compared having a reference measurement Pre f of a directly supplied ASN(x) (bypassing the TPS63031) at three.3 V to calculate the converter efficiency.
