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{{TechSidebar
{{HABEES-sidebar
| header = Oscar
| header = Oscar
| img link = File:oscar.JPG
| img link = File:oscar.JPG
| techline = Balloons Core Avionics
| techline = Balloons Core Avionics
| version = Generation I
| version = Generation I
| name = Oscar
| name = Oscar (the grouch)
}}
}}
The '''Balloons Gen 1 Avionics Platform''' is the first core avionics suite developed by HABEES. Named ''Oscar'', this avionics suite flew on a failed technology demonstration in SSI-39, followed by a successful demonstration in SSI-40. As the first core avionics suite, it set the expectations for features to be included in subsequent revisions.
The '''Balloons Gen 1 Avionics Platform''' is the first core avionics suite developed by HABEES. Named ''Oscar'', this avionics suite flew on a failed technology demonstration in SSI-39, followed by a successful demonstration in SSI-40. As the first core avionics suite, it set the expectations for features to be included in subsequent revisions.
=== Top Sheet ===
=== Top Sheet ===
[[File:oscar_raw.JPG | right| thumb | <center> Oscar PCB </center>]]
The top sheet displays the overarching hierarchy of the avionics board. Only perimeter Teensy pins were utilized, hence pins 24-33 and A10-A14 are NC. The GPS was connected to Hardware Serial 1 over pins 0/1. Pin 2 was driven low when SD card was detected (output of the Micro SD sheet). Pins 3-5 were not utilized. Pins 6-9 were used for RockBlock operation, although NETAV & SLEEP were not used for actual operation, and may be discarded in the future. Pins 10-13 were used to define the SPI Bus, and pin 10 was used as the Micro SD chip select. As seen in the bottom left, pinouts were supplied for I2C and SPI. VIN was supplied with +5V from the boost circuit. Two decoupling caps for +3.3 and +5 were sourced local to the MCU. Pins 22-20 were defined as chip selects for the thermocouple and BMP 280's (22 for thermocouple, 21/20 for BMP280). Pins 19/18 defined the I2C bus. The I2C bus had five total devices: Two MS5803's, One MPL3115A2, One MCP23017 multiplexer, and one RTC IC. Pin 16 connected to the battery protector (LTC4218) power good indicator. Pins 15 and 14 were used for current monitor (via 4218) and battery voltage detection.
The top sheet displays the overarching hierarchy of the avionics board. Only perimeter Teensy pins were utilized, hence pins 24-33 and A10-A14 are NC. The GPS was connected to Hardware Serial 1 over pins 0/1. Pin 2 was driven low when SD card was detected (output of the Micro SD sheet). Pins 3-5 were not utilized. Pins 6-9 were used for RockBlock operation, although NETAV & SLEEP were not used for actual operation, and may be discarded in the future. Pins 10-13 were used to define the SPI Bus, and pin 10 was used as the Micro SD chip select. As seen in the bottom left, pinouts were supplied for I2C and SPI. VIN was supplied with +5V from the boost circuit. Two decoupling caps for +3.3 and +5 were sourced local to the MCU. Pins 22-20 were defined as chip selects for the thermocouple and BMP 280's (22 for thermocouple, 21/20 for BMP280). Pins 19/18 defined the I2C bus. The I2C bus had five total devices: Two MS5803's, One MPL3115A2, One MCP23017 multiplexer, and one RTC IC. Pin 16 connected to the battery protector (LTC4218) power good indicator. Pins 15 and 14 were used for current monitor (via 4218) and battery voltage detection.
=== RTC ===
=== RTC ===
A DS1307 RTC IC is utilized for the real-time clock. The Teensy 3.2 internal RTC is avoided due to past difficulties/problems. The DS1307 is powered by 5V (no 3.3V variety exists). A 32.768kHz 12.5pF time-keeping crystal X1 is used for the RTC, and a keystone 12mm coin cell holder provides backup power for the RTC. A 100 nF decoupling cap is provided.
A DS1307 RTC IC is utilized for the real-time clock. The Teensy 3.2 internal RTC is avoided due to past difficulties/problems. The DS1307 is powered by 5V (no 3.3V variety exists). A 32.768kHz 12.5pF time-keeping crystal X1 is used for the RTC, and a keystone 12mm coin cell holder provides backup power for the RTC. A 100 nF decoupling cap is provided.
[[File:oscar_full.JPG | right| thumb | <center> Oscar in SSI-39, along with the RockBlock, Battery Pack, and Heater </center>]]
=== RockBlock ===
=== RockBlock ===
The RockBlock uses a 2x3 vertical Molex microfit connector. It is provided +5V, GND, Serial TX/RX lines, as well as connections for the SLEEP & NETAV pins, which are not utilized.
The RockBlock uses a 2x3 vertical Molex microfit connector. It is provided +5V, GND, Serial TX/RX lines, as well as connections for the SLEEP & NETAV pins, which are not utilized.
== PCB Design ==
== PCB Design ==
[[File:Last_flight_space.jpg | right| thumb | <center> SPACE Micro </center>]]
[[File:Oscar_PCB.PNG | right| thumb | <center> Oscar PCB Layout </center>]]
The PCB layout for Oscar can be seen on the right.
The PCB layout for Oscar can be seen on the right. Oscar was notable for its novel shape -- a 3/4 hexagon, designed to fit perfectly in a Gen 1 HABHIVE container and allow some space for routing wiring and positioning a RB/battery pack vertically.
Oscar also notably has battery protection and boost circuits locally, on the bottom right hand side. This is the first and last instance that a Core Avionics suite contains on-board battery protection/boosting. Subsequent power circuits are relocated to an external BMS. Oscar is also notable for very low part density -- this is in part due to its large size, which, although more large than necessary, is defined as such for mechanical purposes. Oscar also features surface mount Molex Microfit connectors, which are replaced in subsequent lines of avionics platforms in exchange for smaller footprint through-hole varieties. Oscar is the first and only avionics suite to only use the perimeter pins of the Teensy 3.2 -- subsequent avionics all use the additional underbelly pins.
Oscar has three mounting holes, designed for #8 bolts, for mechanical integration into HABHIVE.
== Milestones ==
Oscar is the first-ever PCB developed for the Balloons Core Avionics Suite. It is also one of the most feature rich and modular avionics systems produced within SSI at the time of its creation. Every system on Oscar is functional and flight-proven -- the only subsystem that was not proven was the FET current sensing, which was removed.
== Problems ==
Oscar, as the first in the line of avionics suites, was riddled with problems in its production, design, execution, and testing.
Key problems included:
* Initial reflow of Oscar resulted in many shorts, most notably on the MCP23017 and LTC4218.
* Very small grid spacing in Altium resulted in multiple pins on the I2C multiplexer being unconnected to anything. All three address selection pins were short-soldered together, and greenwired to the backup battery ground pad.
* Vigorous whicking removed a trace & via leading to FET 1, resulting in FET 1 being unusable.
* Poor reflow of pressure sensors resulted in the removal and subsequent re-soldering of all pressure sensors. Only one of the two BMP280's and one of the MS5803's is functioning at final flight time. The MPL3115A2 is functional for some period of time, and non-functional by time of flight.
* Improper design of FET LED circuit.
* The GPS breakout TX/RX lines are swapped; they are later swapped on the breakout itself, to allow for the PCB to remain unmodified.
* Despite having SPI pinouts, there are no chip select pinouts.
* The thermocouple is connected backwards, the ferrite beads were of the improper frequency rating, and the diodes had to be removed.
== Flights ==
=== SSI-39 ===
[[File:ssi40oscar.jpg | right| thumb | <center> Oscar, during SSI-40 </center>]]
SSI-39, the inaugural flight of Oscar, was a flight plagued with unfortunate mistakes, and some poor decision making. Flight software for Oscar was completed approximately 4 hours before departure from campus, fully functional. En route to launch site, additional components were added, including ascent rate calculation, as well as GPS flight mode and a few other features.
At launch site, extensive debugging and checking took place to verify the system. GPS lock was seldom obtained initially, but was later regained with high frequency. RockBlock communication was very sparse, often losing lock and communicating on average every 15-20 minutes rather than the programmed 2 minute interval. Debugging, configuration, and testing took place on-site until 1 pm -- two hours past the 11 am expected launch time. At this point, the system was performing nominally outside of habhive, but, upon insertion, worked sporadically, until the flight software terminated randomly. At one point, it was determined that the time was getting late and the payload must be launched. A communication was received, and it was determined that the payload was ready for flight. After release, no more communications were received.
Upon return to campus, root cause of failure was analyzed. The problem lied in the GPS antenna being loose -- contact with pressure sensor housing of the BMP280 or MPL3115A2 caused flight software to crash. The flight provided no data logs, and no communications.
Aside from the antenna problem, the system was nominal.
=== SSI-40 ===
SSI-40, taking place shortly after SSI-39, was an exact re-flight of Oscar, with the modification of having the GPS antenna taped to a habhive wall. The system performed nominally from prep to launch and throughout the entire flight. Communications were frequent, coming in often 30 seconds apart. The payload successfully recorded and transmitted flight critical parameters for the entire duration of the flight, including internal and external temperatures, altitude, ascent rate, power state, and more. A successful cutdown was also triggered at 25 km using a custom FET and nichrome wire. A heater was included but did not activate during the flight.
The payload was recovered floating atop algae in an irrigation canal. All flight electronics remained in nominal state at time of recovery. The Micro SD card contained thorough data from throughout the entire flight.
[[Category: High Altitude Balloons]][[Category: HABEES]]