CubeSatPowerAnalyticsUnit

TiSAT CubeSat - Power Analytics Unit

This repository contains the design and development files for the Power Analytics Unit of the TiSAT CubeSat project. The primary objective is to monitor and analyze the power consumption of various sensors integrated into the satellite.

Project Overview

The core of this project is a custom-designed power measurement circuit. It utilizes a shunt resistor to measure minute currents and voltage levels across specific circuit branches, enabling precise power calculation.

Since the satellite is equipped with solar panels for battery charging, the power management logic accounts for both energy harvesting and consumption cycles to ensure balanced power distribution.

Current Progress

• Circuit Design: Completed the schematic and PCB layout using KiCad.
• Component Selection: Selected specialized ICs for precision current sensing (INA199A1) and the STM32L431KC microcontroller.
• Manufacturing & Assembly: The custom PCB has been fully manufactured, and all SMD and through-hole components (including critical high-precision IC packages) have been successfully soldered and assembled.
• Firmware Communication Loop: Established a low-level hardware communication interface between the STM32 MCU and a Raspberry Pi Pico W using single-wire, half-duplex UART with inverted polarity (open-drain transmitter, 9600 baud). The firmware is bare-metal and uses blocking (polling) USART access.
• Ping-Pong Verification: As the first step, confirmed working end-to-end UART communication on the shared single-wire bus — the STM32 replied pong\n to every ping\n sent by the Raspberry Pi Pico W, verifying the physical link between the two microcontrollers.
• Shunt Resistor Calibration: Performed a 4-point (Kelvin) measurement to precisely determine the shunt resistor's true value (52.2865 mΩ, not the nominal 50 mΩ).
• TiSAT Protocol Implementation: Replaced the raw ping-pong test with the full, checksum-validated TiSAT frame protocol ($/# direction, 3-character module ID, payload, checksum, terminator), matching the shared master-side specification used across the TiSAT project's other modules.
• ADC-Based Power Measurement: Implemented calibrated ADC sampling of the shunt voltage — using the internal VREFINT reference to compensate for real VDDA deviation and 64x oversampling to suppress noise — converting the INA199 current-sense amplifier output into live current, voltage and power readings, delivered over the GETDATA command.
• Current Calibration & Verification: Calibrated the current measurement against known reference currents with a straight-line (linear regression) correction, and added a no-load threshold so an unloaded module reports exactly 0. Verified on 38 reference points between 1 mA and 200 mA: the worst absolute error is 0.194 mA (about 0.1 % of the 200 mA range), the relative error is below 0.3 % from 50 mA up and reaches 8.7 % only at 1 mA, where one ADC step (about 0.31 mA) limits the resolution.

Software Architecture & Development

The software side consists of the low-level firmware of the onboard microcontroller and a test master for the receiving subsystem:

1. Custom HAL (Hardware Abstraction Layer): Bare-metal foundational drivers written from scratch in C++ to manage the MCU peripherals (RCC, GPIO, ADC, USART), without any vendor HAL or RTOS.
2. Request-Response Communication: The STM32 acts as a Slave: it waits for a command frame from the Master (ping, GETDATA) and answers it over the shared open-drain bus. Reception and transmission use polling in the main loop, which keeps the firmware simple and its timing predictable.
3. Calibrated Measurement Pipeline: Every GETDATA request is answered with fresh, calibrated current, voltage and power values, based on the VREFINT-compensated, 64x oversampled ADC readings and the linear-regression current calibration.
4. Subsystem Master (Test): A CircuitPython-based test master on the Raspberry Pi Pico W periodically sends ping and GETDATA frames, prints the replies, and toggles a diagnostic heartbeat LED.

About the Author

This project is being developed as part of my undergraduate thesis at the University of Szeged (SZTE), under the guidance of my supervisor.

It serves as a practical application of my ongoing studies in C, C++, and Assembly. This mission allows me to bridge the gap between hardware design and low-level software engineering while contributing to the TiSAT satellite mission.

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