Science Board
Reads the atmospheric sensors on the science payload and publishes their readings on the CAN bus.
Firmware lives in src/science.
Hardware
Five sensors. Four sit on one I2C bus; the UV sensor is read through the ADC.
| Sensor | Part | Bus | Address | Publishes |
|---|---|---|---|---|
| Temperature, humidity, pressure | BME280 | I2C | 0x77 |
temperature, humidity, pressure |
| Carbon dioxide | SCD4x | I2C | 0x29 |
co2 |
| Oxygen | I2C | 0x70 |
oxygen |
|
| Ozone | I2C | 0x73 |
ozone |
|
| UV | analog | ADC | uv_index |
Behavior
| Timer | Rate | Purpose |
|---|---|---|
htim2 |
400 ms | CO2 sensor transmit |
htim3 |
100 ms | CO2 sensor receive |
htim6 |
500 ms | publish SCISensorData |
htim7 |
500 ms | I2C watchdog |
htim15 |
100 ms | publish SCISensorState |
htim16 |
1000 ms | retry faulted sensors |
Every sensor derives from ScienceSensor (src/science/Inc/ScienceSensor.hpp), which gives them
all the same four-part interface:
| Method | Purpose |
|---|---|
init() |
configure the device; returns false if it does not respond |
poll() |
start an acquisition |
update() |
consume the result and store it |
restart() |
re-run init() on a faulted sensor and clear the fault if it succeeds |
Acquisition is asynchronous: poll() starts a transfer and the completion interrupt drives
update(), so the main loop never blocks on a slow sensor. The CO2 sensor gets its own transmit
and receive timers because its exchange is slower than the others.
Fault Handling
Each sensor carries a state flag. One that fails to respond is flagged and the board keeps running
with the rest, publishing the flags so the rover knows which readings to trust. A 1 Hz timer
retries flagged sensors through restart(), so a sensor that browns out or is reseated recovers on
its own without a board reset.
CAN Interface
The board publishes to host 0x10 from node 0x40, both fixed in
src/science/Inc/config.hpp.
Receives
| Message | Base ID | DLC | Signals |
|---|---|---|---|
SCIResetCommand |
0x80510000 |
1 | reset, clear_faults |
Sends
| Message | Base ID | DLC | Signals |
|---|---|---|---|
SCISensorData |
0x80600000 |
32 | uv_index, temperature, humidity, pressure, oxygen, ozone, co2 (seven 32-bit signed values) |
SCISensorState |
0x80610000 |
1 | uv_state, thp_state, oxygen_state, ozone_state, co2_state (one bit each) |
clear_faults clears the sensor state flags without restarting the board; reset restarts the
MCU.
Note
Science implements neither ESWConfigCmd nor ESWProbe, so it cannot be probed or configured
over CAN.
Configuration
None over CAN. There is no config/science.yaml; the CAN IDs are compile-time constants in
src/science/Inc/config.hpp, so changing them means rebuilding and reflashing.
I2C Notes
The BME280 needs its factory calibration coefficients read out of NVM at startup before any reading
can be converted to physical units, which is why init() does several blocking reads before the
sensor becomes usable. The CO2 sensor has CRC checking disabled during initialization.
See Communication Protocols for background on I2C itself.
Building
./scripts/build.sh --src src/science --preset Debug
./scripts/build.sh --src src/science --preset Debug --flash
Warning
src/science is not in ci.json, so it is not built by CI. Build it locally before
pushing.