## 3 Hardware Description
### Primary Node  
The primary node is an autonomous battery powered system controlled by its own processor (see Figure 6). It manages the secondary node's communication reception and the exchange of information  
Figure 5: Secondary node.  
with the base station. The node is equipped with a GPS, a 433 MHz receiver and a 166 MHz transceiver.  
The primary node is governed by an ARM-7 microcontroller selected because: _i)_ its low cost and consumption, _ii)_ the internal peripherals can be independently controlled and therefore the consumption can be adjusted to the needs of the peripherals, _iii)_ it allows the implementation of a real time operating system, _iv)_ it is a well studied architecture and _v)_ it has a GCC compiler.  
Moreover, the board has been designed in such a way that all external peripherals (i.e. GPS and radios) are power-controlled by the microcontroller. When no peripheral is active and the microcontroller is in sleep mode, a minimum consumption of 20 \(\mu\)A at 3.3 V is achieved. For each peripheral, the typical consumption when active is shown in Table 1. The board includes a 64 Mbit flash memory controlled through an SPI bus. This memory is in charge of storing the information provided by the secondary nodes for its transmission to the base station. In the board's design we have actively pursued _i)_ low consumption and _ii)_ miniaturization. Therefore, each of the internal modules explained below tries to follow the aforementioned characteristics. Moreover, because of the miniaturized components, the board has a size of 9x5 cm\({}^{2}\) which fits the specifications of being carried by the target mammals.  
A _u-blox_ GPS module is integrated into the board. This GPS module allows a connection time of less than one second which reduces the position acquisition and therefore saves power. It has a -160 dBm  
\begin{table}
\begin{tabular}{c c c} \hline Working mode & Peripheral & Consumption (mA @ 3.3V) \\ \hline \hline Sleep & NONE & 20 \(\mu\)A \\ Standard & NONE & 20 mA \\ Standard & GPS & 150 mA \\ Standard & 433 MHz radio & 22 mA \\ Standard & 166 MHz radio & 146 mA \\ \hline \end{tabular}
\end{table}
Table 1: Consumption characteristics of the primary node.  
Figure 6: (a) Top and (b) bottom view of the primary node.  
acquisition and tracking sensitivity and it is highly immune to jamming. Its low consumption characteristics and miniature size (16.0 x 12.2 mm\({}^{2}\)) make the module suitable for our application. Moreover, the module allows several connectivity options (i.e. UART, SPI, USB and I2C). In our design, the controller communicates with the GPS module through a UART while the USB connector has also been introduced for possible extended developments.  
An FSK superhetorodyne dual-channel receiver has been introduced into the design for the communication with the secondary node. It is tuned to receive at a frequency of 433 MHz and includes a low noise amplifier, an image-reject mixer, a PLL, a local oscillator, a limiting amplifier, a low-noise FM demodulator and a 3V voltage regulator. The module can be switched on and off by the microcontroller to save power. Preliminary results show that the primary-secondary node communication achieves ranges of up to 100 m (see Section 4). A patch antenna as been added to the communication system which allows high communication ranges.  
The long range communication system is implemented with an ISM Band FSK transceiver. It is designed for operation in the low UHF and VHF bands and a 166 MHz band has been chosen. In the primary-base station communication we emphasize maximum range, simple interface and high data rates. The transceiver allows a frame rate of up to 200 kbps and has a -119 dBm sensibility. Moreover, the transceiver allows a programmable output power from -16 dBm to +13 dBm in 0.3 dBm steps. The antenna should be located on the top of the supporting animal, therefore an SMA connector has been added for the 166 MHz antenna. This connector allows the antenna to be wired to an upper position, for example in a specific collar.