Question

Consider a WSN node such that every 5 sec interval there is radio communication for 0.1 sec and sensor reading for 0.5s. Assume the node draws 20 mA when the radio is activated, 5 mA when the node is reading a sensor, and 0.5 mA when the node is sleeping. We use two AA batteries of 1.6 V and 2000 mAh connected in series Part (10 points): Calculate total charge drawn by the node in mAh over a 24 h period. Part 2 (10 points): Assume there is no energy harvesting at the node to recharge the batteries. Calculate how many days it would take to discharge full batteries Part 3 (5 points): Assume the node can harvest 10 mAh every day from a solar panel. How long will the batteries last? Part 4 (5 points): Assume the node can harvest 10 mAh every day from a solar panel and the radio transmission power is tuned down to only 10 mA when activated. How long will the batteries last?

Answer 1

Time period = 5 sec = T due to radio communication for 0.1 sec, charge = 0.1 times 20 mA sec Q_RC = 2/3600 m Ah [changing 1 sec = 1/3600 hour] due to sensor reading for 0.5 sec, charge = 0.5 times 5 m A sec Q_SR = 2.5/3600 m Ah [1 sec = 1/3600 hour] due to sleep for (5 - 0.1 - 0.5) sec or 4.4 sec, charge = 4.4 times 0.5 m A sec Q_sleep = 2.2/3600 m Ah Total charge in a time period T, Q_T = Q_RC + Q_SR + Q_sleep = 2/3600 + 2.5/3600 + 2.2/3600 Q_T = 6.7/3600 m Ah In a days 1.p 24 hrs, total time cycle = 24 times 3600/5 (a) Total charge in a day = Q_T times total time cycles = 6.7/3600 times 24 times 3600/5 Q_24h = 32.16 m Ah (b) two batteries of 1.6v & 2000 m Ah V = 1.6 times 2 = 3.2v Q_Bat = 2000 m Ah.