Power supply: The node is supplied by two Li-ion batteries of D type (3.6 V, 15,000 mAh) wired in series. E1in Fig. 2 shows the resultant power source. Battery power supply is stabilized to 3.3 V by low-dropout voltage regulator ADP3335, DD1, which accepts input voltage in 2.6–12 V range. The challenge in the selection of power supply circuit consists in the gas sensor which is a measuring device influenced by ambient conditions and noise. In this specific case, the sensor node is based on the catalytic sensor that must detect even negligible deviation of a complicated analogue signal.
Linear regulators have low level of noise with respect to DC/DC, but at the same time are characterized by low efficiency due to the power dissipation on a regulating element. For example, the effective measuring circuit voltage response lies in the range of tens of V up to a few mV (depending on a design of measuring circuit). That is why the main objective of the power supply circuit is to ensure the low level of noise in the circuit.
To increase the long-term operation of sensor node we plan to employ the energy scavenging technology, e.g. harvesting of indoor/outdoor light [26], for the batteries’ replenishment.