Near Space Engineering

The NASA Ames Research Center is responsible for various cube satellites, suborbital experiments, and high altitude balloons. The goal of this project is to design a new revision of a circuit board that both enables a modem to connect to the internet and supports auxiliary equipment for NASA’s activities.

Background
Continuing the University of Idaho's partnership with NASA, the aim of this project is to develop an advanced, general purpose, telemetry system for future space and high altitude balloon flights. The novel Iridium 9523 modem would enable a vast array of new research opportunities.

Deliverables
Design and program a PC104 telemetry board driven by an Intel Edison. The board would at minimum support an Iridium 9523 data modem, a camera, and have enough general purpose output to drive other miscellaneous equipment such as a cold gas system.

Specifications
The following table contains the specifications for both the new revision being developed and the old revision.

Dip Trace Software
Dip Trace is used to design a printed circuit board (PCB) layout. A PCB electrically connects all the necessary components in a compact space.

Intel Edison
The Intel Edison is the processor that will be used for this project. It contains a high-performance, dual-core CPU and a single-core microcontroller that supports complex data collection in a low-power package.

Overview
The purpose of this board is to be an efficient, low-power support that performs maintenance functions while the rest of the satellite is sleeping. It has a central microcontroller in a web of low-power peripherals that can be activated at need but remain sleeping otherwise. IO expander peripherals are used when possible to leave the microcontroller’s communications buses free for communicating with external devices.

Battery Connector
The 9155 MOBO 2.5mm Pitch Right Angle Battery Connector is rated at 3 amps. The connector’s design is small and compact to minimize its profile yet functionally stable having a contact point at 2.20mm above the PCB.

Battery Charger
The LTC 4000-1 is a controller that converts many externally compensated DC/DC power supplies into full-featured battery chargers with maximum power point control. The LTC4000-1’s battery charger includes: accurate (±0.25%) programmable float voltage, selectable timer or current termination, temperature qualified charging using an NTC thermistor, automatic recharge, C/10 trickle charge for deeply discharged cells, bad battery detection and status indicator outputs. The battery charger also includes precision current sensing that allows lower sense voltages for high current applications.

Thermocouple
The MAX31850 is the integrated circuit for the thermocouple. Communication with the master microcontroller is over a 1-Wire bus that by definition requires only one data line (and ground) for communication. Operating power can be obtained directly from the data line (“parasite power”), eliminating the need for an external power supply.

Each device has a unique 64-bit serial code, which allows multiple units to function on the same 1-Wire bus. Therefore, it is simple to use one microcontroller (the master device) to monitor temperature from many thermocouples distributed over a large area.

H-Bridge Motor Driver
The DRV8835 has two H-bridge drivers, and can drive two DC motors or one stepper motor, as well as other devices like solenoids. The output driver block for each consists of N-channel power MOSFET’s configured as an H-bridge to drive the motor winding. An internal charge pump generates needed gate drive voltages.

The DRV8835 can supply up to 1.5-A of output current per H-bridge. It operates on a motor power supply voltage from 0 V to 11 V, and a device power supply voltage of 2 V to 7 V.

Buck Regulator
The BD86120EFJ is synchronous buck converters. The device integrates power MOSFETS that provide a each maximums current output current continuous load current over a wide operating input voltage of 4.5V to 18V. Current mode operation provides fast transient response and easy phase compensation.

Solar Panel Connections
Solar panels will be mounted perpendicular to the board on all four edges. They will have bare copper pads, ground and power, running down the center. The power board will have spring-loaded connectors on each edge that will draw power from the pads on the back of each solar panel.

Software
The software for this circuit board will need to facilitate a number of housekeeping and communication tasks. Our code needs to collect sensor data from the thermocouples, IMU, barometer, batteries, and solar panels. The software must then be able to broadcast the data via the Iridium (long­range) and XBee (short­range) modems. In addition to broadcasting the housekeeping data, the software must also be able to interpret incoming commands from the Iridium modem. These commands will include tasks such as disabling power outputs and temporarily delaying Iridium transmissions.

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