Hardware

The OBDH board of the nanosatellite consist of six main sub-modules:

• Central Processing Unit (MCU: CPU + RAM + Program Flash)
• Non Volatile Memory (Mission Data)
• Current Drivers (Active ADCS control)
• Inertial Measurement Units (IMU)
• Current Sensing (Photodiodes reading and OBDH current cumsumption)
• Interfaces with external modules (UART, I2C and GPIO)

There is direct connection between the OBDH and all the other modules of the satellite:

• EPS
• TT&C
• Antenna
• Solar Panels
• Payloads

Each interface is presented in details in the subsequent sections. The general diagram of the OBDH board is presented below:

Central Processing Unit

The sub-module that executes the main code of the OBDH consists of a SoC that contains a CPU, RAM Memory and Flash Memory (used for program storage and non-volatile status registers). The chosen MCU is a low power 16-bit RISC (MSP430F6659IPZ) from Texas Instruments. It contains seven power comsumption operation modes, four 16-bit timers, 12-bit ADC and DAC, six universal serial communication interfaces (USCIs), a real-time clock (RTC) block and up to 74 I/O pins. The operating clock of the OBDH module is 32 MHz.

Together with the microcontroller there is a External Voltage Monitor with Watchdog Timer (TPS3823-33QDBVRQ1) to ensure a certain level of voltage to power up the system and to provide a redundant Watchdog. Also a Voltage Reference IC (REF5030A-Q1) to assure a clean reference for the ADC readings.

Non Volatile Memory

To retain data the OBDH uses a SD card and memories IC's. The micro SD Socket is the Molex 5031821852. The memories are a 128MBit Nor Flash (IS25LP128-JBLE).

Current Drivers

The current drivers used are two H-bridges(DRV8833). They control the Magnetorquers from NanoPower P110 Series solar panels according ADCS logic control.

Inertial Measurement Units

The IMU module is composed by two 9 axis inertial measure units for redundant readings. A Invensense MPU9250 and a Bosch BMX055.

Current Sensing

The Current Sensing module have three Rail to Rail Op Amps (TLV341AIDBVR) for the sun sensors readings. And a Current Sense amplifier (MAX9934TAUA+) for the OBDH total current consumption.

Interfaces

In order to exchange informations between other satellites modules was established a PC104 interface using two 52 pins connector(ESQ-126-39-G-D). For the JTAG and all debugging interfaces the Through Hole pin Headers 4-103327-5 were used. And for the communication with the solar panels three (one for each) 12 pins Molex 0533980671.