Specifications (from the EE Team)

Overall Hardware Architecture (taken from https://uwarg-docs.atlassian.net/wiki/x/AoCsmQ )

Background

The drone uses a battery pack containing 12 cells, where 2 groups of 6 cells are each connected in series (hence 6S).

Each group of 6 cells is connected to a battery monitoring circuit.

This circuit measures:

The voltage of each cell
The current delivered by the group
- This is done by forcing the battery to deliver current through a resistor with a tiny resistance. This resistor, called a shunt/shunt resistor, follows Ohm’s law: V=IR
- This implies that I=V/R, which means that the current passing through a shunt is equal to its voltage (which can be measured easily), divided by its resistance (which is a known constant).

And it sends:

We are not exactly sure of everything yet.

Battery-related information relating to the voltages and currents
The voltage and current information are sent as 2 analog signals, which our microcontroller converts to digital ones via an Analog-to-Digital Converter (ADC).
Some other information is sent via the I²C protocol

Description

MCU (STM32xX) in the top right is the microcontroller that we are writing the code to
Its job is to translate the messages it receives from the BQ76925 6s LiPo Battery Monitor boards and send the corresponding messages to the flight controller (FC) using the CAN protocol

Why are we making this?

The FC needs this information to make other decisions, e.g. if a part is consuming too much power, or when to land

Specific Hardware Information (taken from https://uwarg-docs.atlassian.net/wiki/x/HYBXq)

The ports we are interested in:

PA9: SCL_1, Serial Clock line for I²C 1
PA10: SDA_1, Serial Data line for I²C 1
PA7: SCL_2, Serial Clock line for I²C 2
PB4: SDA_2, Serial Data line for I²C 2
PA12: CAN_TX, Transmit line for CAN
PA11: CAN_RX, Receive line for CAN
PA3: OVERCURRENT, receives 5.5 V when an overcurrent occurs, and 0 V otherwise

Speculated ports:

PA5: VCOUT1_FILT, receives 1.47-1.53 V (REF_SEL=0) / 2.94-3.06 V (REF_SEL=1), representing the cell voltages for cells 1-6
PB0: ADC1_FILT, receives 0.25-1.25 V (REF_SEL=0) / 0.5-2.5 V (REF_SEL=1), representing the cell current for cells 1-6, as measured by a 1-milliohm shunt
PB1: VCOUT2_FILT, receives 1.47-1.53 V (REF_SEL=0) / 2.94-3.06 V (REF_SEL=1), representing the cell voltages for cells 7-12
PA2: ADC2_FILT, receives 0.25-1.25 V (REF_SEL=0) / 0.5-2.5 V (REF_SEL=1), representing the cell current for cells 7-12, as measured by a 1-milliohm shunt

\uD83E\uDD14 Current Roadblocks

Libcanard has a high learning curve. Neither the DroneCAN website nor the Libcanard repo has beginner-friendly tutorials. YouTube videos also won’t help directly

Tasks Break Down:

✅ Action Items

etc.

\uD83D\uDEA9 Milestones

Understand project specifications
Understand the I²C protocol
Understand the CAN protocol
Understand DroneCAN
etc.

Open Questions

What is REF_SEL set to for the battery monitoring boards?
Are our speculated ports correct?
Why are we reading the battery and voltage information via both I²C and analogue pins?
How should the MCU beacon itself to the FC (i.e. so that the FC is aware that the MCU on the power module is there)?
What should be sent over CAN?

\uD83D\uDD17 Reference materials

Relevant protocols

I²C: I2C - Inter-Integrated Circuit
- I²C is all about registers (i.e. memory that can be accessed by an address)
- Each I²C peripheral has its own register map (i.e. what the registers are used for, such as storing the voltage of a cell)
- To read data from a peripheral, you send an address to it, and it will respond with data
- To write data to a peripheral, you tell it which address to write to, and what data to write
CAN:
- A general description of CAN: https://uwarg-docs.atlassian.net/wiki/x/BgDPlw
- DroneCAN: a protocol built on top of CAN to communicate information between drone parts and the FC: https://dronecan.github.io/
  - Libcanard: an implementation of DroneCAN for low-end microcontrollers. An example code on how to use it: https://github.com/dronecan/libcanard/blob/master/examples/SimpleNode/simple_node.c
- A helpful presentation on CAN: https://docs.google.com/presentation/d/12i6TiUuXQw5mO2u3pq8DMXTD1bCRe8rJtzVZRk6pDz0/edit?usp=sharing
- A helpful document on CAN applications: https://uwarg-docs.atlassian.net/wiki/x/AwA8q

6S Power Module