# Effect of Ambient Temperature on Impedance-Based Physiological Activity Evaluation of Zelkova Tree
## 3 Tree Physiological Activity Monitoring System
### TPAM System Hardware  
Figure 5a shows the top diagram of the TPAM system. The system consists of two parts: the on-tree system and the hub system. The on-tree system is attached to a tree and measures various data and transmits it to the hub system. The hub system receives measured data, displays it on the graphic user interface (GUI), and stores it in the storage device. The on-tree system consists of a measurement board (TPAM_PCB), a battery, and components located outside the measurement board (solar panel, light sensor, probes). Figure 5: Tree physiological activity monitoring (TPAM) system: (**a**) top block diagram of TPAM system and (**b**) implemented PCB (TPAM_PCB). The measurement board TPAM_PCB consists of a power supply unit, a sensing unit, a microprocessor, and a wireless communication unit. The solar cell harvesting chip in the power supply unit receives power from the solar panel and charges the battery. And the DC/DC converter and low dropout regulator (LDO) in the power supply unit receive power from the battery and generate various operation voltages required in the measurement board. The sensing unit consists of an on-chip temperature sensor and an impedance readout integrated circuit (ROIC). The microprocessor receives a detection signal from the optical sensor and performs analog-to-digital conversion every 4 min using an internal 12-bit analog-to-digital converter (ADC). The microprocessor also receives detection signals from the battery and performs analog-to-digital conversion every 4 min using an internal 12-bit ADC. The microprocessor receives 16-bit sensing data from the temperature sensor every 4 min via inter-integrated circuit (I2C) communication. The microprocessor receives sensed data from the impedance ROIC every 4 min via serial peripheral interface (SPI) communication. The impedance ROIC was implemented with a commercial chip (AFE4300) and includes current injection, voltage sensing, demodulation, and 16-bit digital conversion functions. The impedance ROIC generates 16 bits of data for each of the five channels, CH1 through CH5. In CH1 and CH2, impedance data are generated using the two-point and four-point measurement methods, respectively, using a probe inserted to a depth of 6 mm. In CH3 and CH4, impedance data are generated using the two-point and four-point measurement methods, respectively, using a probe inserted to a depth of 13 mm. CH5 generates impedance data measured from a standard resistor mounted on the TPAM_PCB. Additionally, all channels (CH1 to CH5) generate impedance data for the current injection at four frequencies (8 kHz, 16 kHz, 32 kHz, and 64 kHz). When the microprocessor writes a specific register combination to the impedance ROIC, the impedance ROIC outputs a current of 8 kHz, measures the data on CH1, and transmits the data to the microprocessor. When transmitting data from the impedance ROIC to the microprocessor, a total of 32 bits of data are transmitted, including 16 bits of the reference resistance measurement value and 16 bits of the impedance measurement value measured at 8 kHz in CH1. Immediately after that, when the microprocessor writes another specific register combination to the impedance ROIC, the impedance ROIC outputs a current of 16 kHz, measures the data on CH1, and transmits the data to the microprocessor. Then, when data are transmitted from the impedance ROIC to the microprocessor, a total of 32 bits of data are transmitted, including 16 bits of the reference resistance measurement value and 16 bits of the impedance measurement value measured at 16 kHz on CH1. In this way, 32 bits of data are generated for five channels and four injection current frequencies every 4 min, collecting a total of 640 bits of data. Whenever new data are collected from each sensor, the microprocessor constructs a data packet and transmits it to the wireless communication unit through I2C communication. The wireless communication unit transmits the data packet received from the microprocessor to the hub system using ZigBee wireless communication.