Matthew Glazer

The mainboard for this project will control and interact with all other parts of the HAB payload. This board features the same MCU setup as the Teensy 3.2, allowing a range of people to be able to use this hardware. Other features include an altimeter, 9DOF IMU, onboard temperature sensor and three external thermistors, 64Mbit of onboard flash and MicroSD card support and finally multiple MOSFET and relay controlled switched power sources. These allow for nichrome cutoff systems as well as handling requirements of other tagalong payloads.

This view of the schematic details the sensors used in the design. Included are an altimeter sensor, 9DOF IMU and temperature sensor, as well as three external thermistors.

This view shows the data/input output as well as power control available onboard. RS485, CAN, I2C and a UART are broken out from the MCU and are available to the end user. A microSD card slot is available for data logging in tandem with the onboard flash storage. Two relays and three mosfet controlled power outputs are available supplying a range of voltages from 3.3V, 5V, protected Vbus and direct battery as well as a user input supply. These can all be triggered by the MCU for any need.

3D view of the finished board, the dimensions are 8 x 10cm. This revision one of the board will allow for testing, software development and to continue HAB launches. Revision two will be redesigned to standardize the mounting points and to better use the space available, as well as design in any changes required due to initial testing.

Board assembly complete, all work was done at the on campus SMD lab over the course of two days, about 10 hours in total. Assembly went smoothly, however it was discovered that three patterns were flipped and one misplaced. Debugging and troubleshooting allowed for the use of all but one sensor. More debugging is required for the SD card interface, as it was too unstable for use. Lessons learned: 1) Board design takes a while, take breaks to clear your thoughts as this will help avoid issues. 2) ALWAYS, ALWAYS double check all of your footprints, its depressing finding an inverted pad you thought was fine. 3) Extensive board reviews should not be dropped due to deadlines, move the deadline back, make sure they happen. A note on number three, I discovered a double edged sword being the only electrical engineer on a team. You can design great electronics, but you cant become complacent. If no one else on your team can help you, find someone that can.

The board powered up for the first time! The micro-controller setup worked flawlessly, as did most of the board. The primary function for the mission was operational, and while there were issues with the rest of the board, the HAB flight went flawlessly.

Due to a misunderstanding with the MCU's datasheet, the MISO/MOSI lines for the SPI were flipped. This is the fix, which enabled for at minimum basic detection of SD cards. While it didn't solve the problem, I learned much on how to debug and diagnose hardware issues. Applying the use of an oscilloscope and a logic analyzer, I was able to narrow down issues with communication and greatly expanded my knowledge of logic analyzers. These issues are planned to be fixed in the Rev 2 hardware of this board. As long as all goes well, this next revision will be able to fix all the current issues and expand the options SPEX has available to its HAB team.