## 2 Materials and Methods
### Hardware and Related Software  
In this study, we delve into the possibilities of low-power sensing using BLE as our wireless communication strategy. Our approach involves implementing the sensor node system across three distinct microcontroller platforms. We aim to conduct experimental comparisons of their ultra-low-power performance, ultimately enabling us to identify the most power-efficient microcontroller. Our experimental investigation involves the following microcontrollers:  
Figure 3: Illustrative presentation of the sensor node broadcast operation (**a**), together with a scheme of internal sub-units of the wireless sensor node (**b**). * The \"TI-Launchpad\" development board, which is based on the CC2650 microcontroller from Texas Instruments Inc.(r), Dallas, TX, USA. * The \"Feather-nRF52 Bluefruit-LE\" development board, utilizing the Nordic Semiconductor nRF52832 microcontroller and produced by Adafruit Industries(r), New York, NY, USA. * A \"Custom AVR\" development setup, employing the Atmel ATmega328p microcontroller from Microchip Technology Inc.(r), Chandler, AZ, USA. The selection of microcontroller platforms is driven by their performance metrics, specifically their capability to operate at the lowest possible voltage levels, ensuring high efficiency. Additionally, ease of access and widespread availability in the market are key considerations in the decision-making process. Through these comparative experiments, we seek to determine the microcontroller platform that offers the best power efficiency for our sensor node system. The microcontroller is at the center of the sensor node system, and it interacts with various peripheral devices necessary for the functionality of the node. These peripheral modules are essential components that must be interfaced correctly with the MCU, utilizing specific digital interfacing protocols. Specifically, we intend to employ the following modules in conjunction with their respective MCU platforms: The BME680 shuttle board, which interfaces with the MCU to enable environmental sensing. The nRF24L01 wireless module, which facilitates wireless communication and data transmission. The TPL5110 timer breakout board, which plays a critical role in power management and scheduling tasks. By integrating these modules with their respective MCU platforms, we aim to create a fully functional sensor node system capable of efficient low-power sensing and communication. For environmental sensing, we choose the BME680 sensor provided by \"Bosch Sensortec GmbH(r), Reutlingen, Germany\". This sensor is characterized by its ultra-low-power consumption and is capable of measuring environmental parameters such as humidity, pressure, and temperature and the presence of Volatile Organic Compounds (VOCs) or gases. These measurements collectively offer insights into the quality of the surrounding air [42]. Two of the platforms we choose come equipped with built-in BLE features, whereas the Atmega328p does not. Consequently, for the latter, we require an external BLE device to broadcast the collected environmental data. To fulfil this need, we propose utilizing the nRF24L01 2.4 GHz wireless module from \"Nordic Semiconductor(r). Trondheim, Norway\". This module can be programmed to operate as a BLE device, aligning with the objectives of our present work. To regulate the broadcast frequency of our BLE sensor node, we require an ultra-low-power timekeeping mechanism to wake the MCU up at specified intervals. For the TI-CC2650, an internal operating timer is available even in the lowest power mode, with a power consumption of approximately 50 uA. This offers an alternative option for our operation, which is further investigated in the next section. However, for the nRF52832 and Atmega328p, using an external input as a trigger is the only viable option. Consequently, we rely on the external timer module TPL5110, supplied by Texas Instruments Inc.(r), Dallas, TX, USA.