Cpb

NyanSat

Combined Payload Board

The Combined Payload Board (CPB) is a component of the NyanSat project, designed to interface with a variety of payloads, including imaging, material science experiments, the Attitude Determination and Control Subsystem (ADACS), and the acoustic spacecraft mapping subsystem.

Internal Interfaces

• Mechanical: PC/104 form factor for holes and board outline.
  • SMT components all on bottom side of board; top side for connectors and stacking Raspberry Pi Zero 2W.
• 40 pin spacecraft electrical bus
  • Battery voltage (post-inhibit switches, current sensing, current limiting on OBC).
  • One GPIO: Gating of battery voltage to board except bridge driver
  • One GPIO: Gating of battery voltage to bridge driver
  • I2C
    • I2C-UART Address: 0x90 = 1001 0000
      • Raspberry Pi: controlled by serial from I2C-UART.
      • Pi power controlled by I2C-UART GPIO
      • 3 external power switches controlled by I2C-UART GPIOs.
    • I2C-SPI converter for driver bridges 0x50 = 0101 000X
      • MAX22200 bridge chip select, command select, and enable controlled by I2C-SPI converter.
    • Microcontroller Address: TBD
  • Ground/return path for power and all signals
• Mounting holes
  • 0603 pads from holes to board ground exist; can populate with capacitor (AC-couple to stack), resistor, short, or leave open.

External Interfaces

• 4 versatile analog inputs. provided by microcontroller ADC, 0-3.3V 12 bit 1.1MSPS. Pads on board allow selections of various modes:
  • Divided voltage or pulled towards chosen voltage
  • Resistive termination or known impedance
  • AC coupling
  • Pin alternate functions allow use for digital inputs or timer outputs
• 2 DC (0-5V) or AC-coupled waveform generation channels produced from microcontroller DAC with ~40mA drive capability
  • Controlled by microcontroller; feedback to ADC allows precise control of voltages.
  • Low pass filter: 2nd order with -3dB bandwidth of 100KHz.
• 8 high-side switches of battery voltage for payloads and magnetorquers
  • 3 controlled by GPIO from I2C-UART peripheral
  • 1 controlled by onboard Raspberry Pi computer
  • 4 controlled by onboard Cortex-M0+ microcontroller
• 8 half-bridges with programmable current limits
• 5 pin connection for external I2C peripheral (e.g. magnetometer)
• On Pi: CSI interface for Raspberry Pi camera

Anticipated Use

• Attitude Determination and Control Subsystem (ADACS):
  • Switches: 3 magnetorquers, bipolar (6 half-bridges)
• Acoustic Spacecraft Sounding:
  • Switch: Solenoid, driven by pair of half-bridges
  • Possible switch: MEMS microphone power
  • ADC: 2 channels of MEMS microphone.
• Material science / semiconductor characterization experiment
  • Waveform generation: 2 channels of drive voltages.
  • ADC: 2 channels of measurement.
• Camera
  • Pi/CSI to camera.
  • Possible high powered LED via high side driver.
• Deployables
  • Option open to use high-side switches channels from here for deployment.
  • Consider using this board to energize second deployable resistor for redundancy.

Stored-Program Computing Components

• Microcontroller; used mostly as a smart ADC/DAC.
  • STM32L072RBT6; 32MHz Cortex-M0+ with single-cycle multiplier, 128k flash, 6k data EEPROM, 20k RAM.
• Raspberry Pi Zero 2W; used mostly as interface for camera.
  • Quad-core Cortex A53 64-bit processor, 512MB SDRAM.
  • Wireless capabilities (disabled in flight) can be used for ground troubleshooting.
  • Use SLC microSD card, e.g. SFSD2048N1BN1WI-E-QF-111-STD from SwissBit.

Design Philosophy

• Board's power is gated and will be completely de-powered if a pin on spacecraft electrical bus is not driven high.
• Seperate power gate for magnetorquer full-bridge.
• No high-level sequencing of experiments performed by this board; enabled and commanded from main On-Board Computer (OBC).
• I2C is isolated from spacecraft bus if de-powered or peripheral locks up.
• Large portions of functionality work even if non-volatile memory on a device is corrupted.
  • I2C-UART/GPIO chip does not have nonvolatile memory, and directly controls 4 output switches.
  • I2C-SPI and MAX22200 do not have nonvolatile state.
  • Microcontroller starts up held in reset until explicitly enabled by I2C-UART.
  • If microcontroller is corrupted, Raspberry Pi is capable of reprogramming via on-chip debug features.
  • Pi's power supply is separately enabled by I2C-UART.
  • If Pi filesystem is corrupted, small chance of recovery through failsafe pin (indicates to boot from different part of SD card).

Known Weaknesses & Shortcomings

• No provision to measure power used by this board.
• No real current limiting beyond master current limiting from ADM1176 PMIC on OBC.
  • But: If entire satellite resets due to overcurrent, this board will revert to default state (turned off).
  • 200 mohm resistors and FET Rds do provide a little bit of mitigation of catastrophes.
• Raspberry Pi must be turned on to generate waveforms / run matsci experiment due to board architecture (needs 5V rail).
• Only having 4 ADC is a little limiting.