## 2 Materials and Methods
### Design
#### 2.1.1 Hardware  
Both versions 1.0 (Figure 1) and 2.0 (Figure 2) of the Cryologger ITB were constructed primarily using Adafruit components (Table 1). A complete bill of materials is provided on the Cryologger GitHub repository. Both versions described here share the same functional design but differ in their assembly. In version 1.0, individual components were manually soldered to a protoboard, and hookup wires were used for all circuit wiring. In version 2.0, the Adafruit Feather ecosystem of components was adopted, which consists of main and daughter boards that share a common pinout configuration. This change greatly reduced the complexity of assembly by eliminating the need to measure, cut, route, and solder the many required individual hookup wires (Figure 2). The estimated assembly times for an experienced user are 4 h for version 1.0 and 2 h for version 2.0. Version 1.0 of the Cryologger ITB was based on the Adafruit Pro Trinket microcontroller, powered by the ATmega328P processor (Microchip Technology, Chandler, AZ, USA). The software used to run the Arduino was close to the ATmega328P's memory limit, which necessitated that the code was as memory efficient as possible. To overcome these memory constraints, the Adafruit Feather M0 microcontroller, powered by the Microchip Technology SAMD21 processor, was selected for version 2.0, which allowed for more complex code and feature-rich libraries to be used. \begin{table}
\begin{tabular}{l l c c} \hline \hline
**Component** & **Product** & **Version** & **Cost (USD)** \\ \hline Satellite transceiver & RockBLOCK 9603N & 1.0, 2.0 & \$272 \\ Satellite transceiver antenna & Maxtena M1621 HCT-P-SMA & 1.0 & \$54 \\ \hline Microcontroller & Adafruit Pro Trinket 3V 12 MHz & 1.0 & \$10 \\  & Adafruit Feather M0 Basic Proto & 2.0 & \$20 \\ \hline GNSS receiver & Adafruit Ultimate GPS Breakout & 1.0 & \$30 \\  & Adafruit Ultimate GPS FeatherWing & 2.0 & \$25 \\ \hline Accelerometer/magnetometer & Adafruit LSM303 & 1.0 & \$15 \\  & Pololu LSM303D & 2.0 & \$8 \\ \hline Temperature/pressure sensor & Adafruit MPL3115A2 & 1.0 & \$10 \\ \hline Real-time clock & Maxim DS3231 SN + Adafruit SMT Breakout & 1.0 & \$16 \\  & Adafruit DS3231 Precision RTC FeatherWing & 2.0 & \$14 \\ \hline Voltage regulator & Pololu 5 V, 2.5 A D24V22F5 & 1.0 & \$12 \\  & Pololu 3.3 V, 600 mA D36V6F3 & 2.0 & \$7 \\ \hline Enclosure & Nanuk 905 & 1.0 & \$74 \\  & Nanuk 903 & 2.0 & \$48 \\ \hline Battery & Tadiran TLP-93121-B-AL1 & 1.0, 2.0 & \$145 \\ \hline
**Totals** & & **1.0** & \$638 \\  & & **2.0** & \$539 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cryologger ITB electronics components and estimated costs current as of December 2023. Taxes and shipping are not included. Total costs for each version are shown in bold. Both versions of the Cryologger make use of the same GNSS receiver, real-time clock (RTC), and accelerometer/magnetometer. The GNSS is based on the MTK3339 chipset (GlobalTop, Kaohsiung, Taiwan), which has a positional accuracy of 3.0 m. Power to this  
Figure 1: Cryologger ITB version 1.0 (a) Hand-assembled electronic components and RockBLOCK Iridium transceiver; (b) Custom 3D-printed electronics enclosure installed in Nanuk case ready for deployment. Figure 2: Assembled Cryologger ITB version 2.0 (foreground) based on the Adafruit Feather ecosystem of components and version 1.0 (background) for comparison. RockBLOCK Iridium transceiver not shown. module can also be easily disabled when the beacon is in deep sleep. Timekeeping and alarms are achieved with the DS3231 SN RTC (Analog Devices, Wilmington, DE, USA), which can maintain a clock accuracy of \(\pm 3\) ppm (equivalent to \(\pm 3\) s of drift over 1 year) across a wide \(-40\)\({}^{\circ}\)C to \(80\)\({}^{\circ}\)C temperature range. The LSM303 DLHC (STMicroelectronics, Geneva, Switzerland) accelerometer (\(\pm 2\) g) and magnetometer (\(\pm 1.3\) gauss) provide pitch, roll, and tilt-compensated heading measurements.