Electrical Power Subsystem (EPS)

The open source hardware for the octanis EPS board can be found at https://github.com/Octanis1/Octanis1-Electronics/tree/master/octanis_eps/v0.4_second_run with its gerber files. The last version to date is named octanis_eps_revised. The Electrical Power Subsystem (EPS) Board is in charge of the power monitoring and delivery. It is driven by a low power MSP430G2544 MCU from Texas instruments. It ensures some critical functions:

• Battery voltage monitoring
• Battery temperature control
• Battery charge and discharge
• 3.3V voltage bus regulation
• Solar panels voltage monitoring
• Solar panels current monitoring
• External modules current motoring
• External modules power supply on TPS2022D switches (X3)
• External modules heaters (X3 including battery heater)
• Power dissipation loop
• Analog entries (X4 including battery temperature)
• I2C bus communication

In case the power capabilities of the rover become critically low, the EPS board is able to take the hand, shutting down all the other modules and becoming the I2C master for a while. These features allow the EPS to restart the Main board or/and the ISS if they become unresponsive. As the EPS is constantly monitoring the current consumption of the external modules it is able to detect a motor stall and tell the Main board so to find which motor is stuck and get the rover back on track. The temperature control of different modules is also ensured by the EPS because it is critical for some modules (eg. the batteries) not to freeze. In theory the EPS is able to develop 3A at 3.3V at full performance.

For clarity hereafter comes a detailed diagram of the inner mode of operation of the EPS board. The EPS is externally connected to the batteries (BT+ BUS) and the Solar panels (SC+ BUS) which provides input power for the whole rover. It receives as well as additional inputs information from external sensors. For instance it receives the temperature of the batteries to ensure a proper monitoring of this parameter required for controlled heating. Finally the EPS is connected on the I2C bus to communicate with the Main Board.