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Smart Cities Group Project

SPS30

1.1 SPS30 Software Handling Logic

Function: HandleSPS30Logic()
Purpose: Periodically reads the SPS30 sensor, updates LED visualization, generates JSON payloads for debug and network posting, and manages a post queue with retry logic.

1.2 Measurement Timing

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unsigned long now = millis();
bool can_measure = now - sps30.last_measurement >= kDataMeasurementInterval;
bool can_update = now - sps30.last_update >= kDataTransmissionInterval;
````

* **Explanation:**

  * Checks if enough time has passed since the last measurement (`kDataMeasurementInterval`).
  * Checks if enough time has passed to update LED and JSON (`kDataTransmissionInterval`).
  * If measurement interval not reached, function returns immediately.

---

## 1.3 Reading Sensor Data

```cpp
SPS30_measurement spsData = sps30.readData();

if (!spsData.available)
{
    DEBUG_WARN("Failed to read from sps30 sensor");
    return;
}

sps30.last_measurement = now;

  • Explanation:

  • Reads the SPS30 sensor into an SPS30_measurement struct.

  • spsData.available indicates if the measurement is valid.
  • During warm-up (~5 s) or communication errors, data is unavailable, and the function exits.
  • Updates last_measurement timestamp on success.

1.4 LED Update

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SpsDataToColor(spsData.mc_2p0);

  • Explanation:

  • Converts PM2.5 mass concentration to an LED color.

  • Only executed if update interval has elapsed (can_update).
  • Provides real-time air quality visualization.

1.5 JSON Payloads

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String prettyData = JsonBuilder::BuildJson([&](JsonDocument &doc)
{
    doc["mc_1p0"] = spsData.mc_1p0;
    doc["mc_2p0"] = spsData.mc_2p0;
    doc["mc_4p0"] = spsData.mc_4p0;
    doc["mc_10p0"] = spsData.mc_10p0;
    doc["nc_0p5"] = spsData.nc_0p5;
    doc["nc_1p0"] = spsData.nc_1p0;
    doc["nc_2p5"] = spsData.nc_2p5;
    doc["nc_4p0"] = spsData.nc_4p0;
    doc["nc_10p0"] = spsData.nc_10p0;
    doc["typical_particle_size"] = spsData.typical_particle_size;
    doc["unix_time"] = modem.getCurrentTimestampMs() / 1000;
}, true);

  • Explanation:

  • Builds a pretty-printed JSON for debug logging.

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String data = JsonBuilder::BuildJson([&](JsonDocument &doc)
{
    doc["mc_1p0"] = spsData.mc_1p0;
    doc["mc_2p0"] = spsData.mc_2p0;
    doc["mc_4p0"] = spsData.mc_4p0;
    doc["mc_10p0"] = spsData.mc_10p0;
    doc["nc_0p5"] = spsData.nc_0p5;
    doc["nc_1p0"] = spsData.nc_1p0;
    doc["nc_2p5"] = spsData.nc_2p5;
    doc["nc_4p0"] = spsData.nc_4p0;
    doc["nc_10p0"] = spsData.nc_10p0;
    doc["typical_particle_size"] = spsData.typical_particle_size;
    doc["unix_time"] = modem.getCurrentTimestampMs() / 1000;
});

  • Explanation:

  • Creates a compact JSON payload for network transmission.

1.6 Post Queue Management

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postQueue.push_back(data);
if (postQueue.size() > kMaxQueueSize)
{
    postQueue.pop_front();
    DEBUG_WARN("Post queue full, dropping oldest data");
}

  • Explanation:

  • Adds payload to a queue for network posting.

  • Ensures queue size does not exceed kMaxQueueSize.
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while (!postQueue.empty())
{
    if (trySendQueue(SPS30path))
    {
        DEBUG_INFO("Successfully sent queued data");
    }
    else
    {
        DEBUG_WARN("Failed to send queued data, will retry later");
        break;
    }
}

  • Explanation:

  • Attempts to send each queued payload.

  • Stops at the first failure; retries on next loop.
  • Ensures reliable data transmission without blocking measurements.

1.7 Key Notes

  • Warm-up behavior: SPS30 measurements are invalid for ~5 s after power-up; spsData.available ensures no invalid data is used.
  • Non-blocking I²C: The function returns if intervals are not reached; communication itself does not block.
  • Decoupled intervals: Measurement and LED/JSON updates are independently timed.
  • Error handling: Logs warnings for failed reads and full queue but continues operation.