## 4 Energy Consumption Model  
Analysis and development of a controller to maintain ENO of a behavior monitor required an energy consumption and harvesting simulation model representing a typical tracking device. The CTT-1000a series, shown in Figure 1, is a 40 mm \(\times\) 100 mm \(\times\) 21 mm wildlife behavior monitor weighing 70 g that was selected for analysis and modeling to develop an ENO controller. Each of the tracking device's energy consuming and harvesting components were broken down in a systematic fashion for modeling and then compared to a fielded CTT-1000a deployed on Golden Eagles in eastern North America. The particular set of data used for validation was chosen because the actual deployed devices experienced a wide variance of harvesting energy and would benefit from a controlled rate. The CTT-1000a wildlife behavior monitor consists of an MSP430 microcontroller, a GPS receiver, a real-time clock, FLASH data storage, a Li-ion battery, a Global System for Mobile Communications (GSM) cellular modem, and solar panel tightly integrated into a single system.  
Measurements of the energy and power usage for each component of the CTT-1000a were performed by using a fixed voltage DC power supply and a high-accuracy digital multimeter (Tektronix DMM-4020). Several of the components included voltage regulators to satisfy input requirements. Therefore, measurements instead of manufacturer-stated current draws were used to gain a more accurate model of the system rather than just the individual components such as only the GPS module. In addition, due to each component utilizing a regulator to produce lower voltages than the battery, current draw to each component was independent of the battery voltage. Therefore, current draw can be used as the main indicator of power consumed and represents a direct translation to battery capacity used without having to consider power.  
The tracking device selected for modeling contains the ability to individually toggle power to components using the on-board microcontroller. Initially, the microcontroller's power consumption was measured in active and sleep mode. Next, each of the other system components were toggled on separately where the microcontroller's active current usage was subtracted out of the measured value since components could not be isolated, as shown in Table 2. All measurements were taken using a DC source set at Li-ion batteries with a nominal voltage of 3.7 V. The component measurement along with operation time allows for an insight of how much total energy would be required for a period of operation. For example: during a 24-h period, there are typically 60 GPS fixes collected that take about 1 min and one cellular modem operation, that to send 60 fixes, takes 2 min. The component usage information is able to assist a designer with an energy impact in that if no energy is harvested, 28 \(mA-hr\) of cellular modem would be used during a day. The modem device was a Telit-865 quad band GSM cellular network node. Taking into account the microcontroller operating during the GPS and modem periods, as well as sleep usage, 185 \(mA-hr\) of battery is used. Therefore, to last at least one day using a configuration of 15-min GPS fixes at 60 per day with one cellular operation, a 241 \(mA-hr\) battery is required.