The idea behind this work was to test the capabilities of using a near-field communication (NFC) tag to store the information acquired through an analogue input of a microprocessor powered by an energy harvesting source.
The setup includes these components:
- Peltier cell
- Energy harvesting system
- Dynamic NFC/RFID tag IC
- Temperature sensor
Energy harvesting system
The capabilities of Peltier cells to harvest energy from differences of temperature between its two sides has already been studied in other posts starting with this link, so I will not develop this part of the work here.
The energy harvesting system used in this project is now based on the outstanding Linear Technologies (now part of Analog Devices) Ultralow Voltage Step-Up Converter and Power Manager LTC3108. This device can work with four selectable output voltages: 2.35 V, 3.3 V, 4. V or 5 V to power wireless transmitters or sensors and a low dropout voltage regulator output (VLDO) to power an external microprocessor. According to its datasheet it can start harvesting energy from voltages as low as 20 mV which is precisely indicated for applications that use thermo-electric generator (TEG) such as Peltier cells. The energy is stored in a bank of supercapacitors connected to two outputs of the LTC3108. Two 1 F supercapacitors in series are connected to VOUT and charged when VAUX has reached 2.5 V. Another two 1 F supercapacitors are connected to VSTORE supporting VOUT and preventing an unexpected drop of voltage due to a high power demand by the load. A picture of the setup for this integrated circuit (IC) is: