Turtle Sense communications board v.0.44

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The Communication board v.0.44 is the controlling circuitry for Turtle Sense. It connects, via a coax cable cable, to one or more Smart Sensors. A piggybacked M2M plug-in telephony board made by Janus enables GPS and cellular communications.

Microprocessor

The microprocessor (U1) is identical to the one on the Smart Sensor board. It controls all the operation of the device. Programmed in C, it manages all the circuitry by:

  • timing events
  • controlling, reading and recording data from the accelerometer IC
  • uploading data to the Comm Board

We selected theTexas Instruments MSP430FR5949 because it is extremely low power and contains 64 K of FRAM memory. The 3.0V power from the Comm Board comes into U1 on AVCC and DVCC. The power ground connections are on AVSS and DVSS. There are three 8 bit I/O ports in the chip, labelled P1.0-P1.7, P2.0-P2.7, and P3.0-P3.7, plus three other I/O pins labelled P4.0, P4.1, and P4.4. Some of these ports are connected to the Janus phone board, the power supplies, and to the coax transceiver (U4 and U5). Many other I/O pins are not used, but are available on optional headers. There are two pins connected to an external crystal (X1). X1, along with C1 an C2, provide the chip with a precise 32.768 KHz clock which is used for the timing functions in the program. The chip also has other internal higher frequency clocks. Another set of pins on the chip, labelled J.0-J.3, -RST, and Test, are used for programming the chip. These pins are connected to a PC via the JTAG connector J2.