PMSA003I: add support for driving SET pin low while not actively taking a telemetry reading (#6569)

* support manually shutting off power to the PMSA003I sensor when we aren't doing a telemetry reading

* add comment about PMSA003I_WARMUP_MS to AirQualityTelemetry.cpp

* fix typos, use arduino gpio defines instead of magic numbers

* support manually shutting off power to the PMSA003I sensor when we aren't doing a telemetry reading

* add comment about PMSA003I_WARMUP_MS to AirQualityTelemetry.cpp

* fix typos, use arduino gpio defines instead of magic numbers

* RAK4631: add PMSA003I_ENABLE_PIN define

* fix indentation

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/modules/Telemetry/AirQualityTelemetry.cpp

@@ -14,6 +14,13 @@
 #include "main.h"
 #include <Throttle.h>
 
+#ifndef PMSA003I_WARMUP_MS
+// from the PMSA003I datasheet:
+// "Stable data should be got at least 30 seconds after the sensor wakeup
+// from the sleep mode because of the fan’s performance."
+#define PMSA003I_WARMUP_MS 30000
+#endif
+
 int32_t AirQualityTelemetryModule::runOnce()
 {
     /*
@@ -34,6 +41,13 @@ int32_t AirQualityTelemetryModule::runOnce()
 
         if (moduleConfig.telemetry.air_quality_enabled) {
             LOG_INFO("Air quality Telemetry: init");
+
+#ifdef PMSA003I_ENABLE_PIN
+            // put the sensor to sleep on startup
+            pinMode(PMSA003I_ENABLE_PIN, OUTPUT);
+            digitalWrite(PMSA003I_ENABLE_PIN, LOW);
+#endif /* PMSA003I_ENABLE_PIN */
+
             if (!aqi.begin_I2C()) {
 #ifndef I2C_NO_RESCAN
                 LOG_WARN("Could not establish i2c connection to AQI sensor. Rescan");
@@ -63,6 +77,20 @@ int32_t AirQualityTelemetryModule::runOnce()
         if (!moduleConfig.telemetry.air_quality_enabled)
             return disable();
 
+        switch (state) {
+#ifdef PMSA003I_ENABLE_PIN
+        case State::IDLE:
+            // sensor is in standby; fire it up and sleep
+            LOG_DEBUG("runOnce(): state = idle");
+            digitalWrite(PMSA003I_ENABLE_PIN, HIGH);
+            state = State::ACTIVE;
+
+            return PMSA003I_WARMUP_MS;
+#endif /* PMSA003I_ENABLE_PIN */
+        case State::ACTIVE:
+            // sensor is already warmed up; grab telemetry and send it
+            LOG_DEBUG("runOnce(): state = active");
+
             if (((lastSentToMesh == 0) ||
                  !Throttle::isWithinTimespanMs(lastSentToMesh, Default::getConfiguredOrDefaultMsScaled(
                                                                    moduleConfig.telemetry.air_quality_interval,
@@ -76,8 +104,18 @@ int32_t AirQualityTelemetryModule::runOnce()
                 // Only send while queue is empty (phone assumed connected)
                 sendTelemetry(NODENUM_BROADCAST, true);
             }
-    }
+
+#ifdef PMSA003I_ENABLE_PIN
+            // put sensor back to sleep
+            digitalWrite(PMSA003I_ENABLE_PIN, LOW);
+            state = State::IDLE;
+#endif /* PMSA003I_ENABLE_PIN */
+
             return sendToPhoneIntervalMs;
+        default:
+            return disable();
+        }
+    }
 }
 
 bool AirQualityTelemetryModule::handleReceivedProtobuf(const meshtastic_MeshPacket &mp, meshtastic_Telemetry *t)

src/modules/Telemetry/AirQualityTelemetry.h

@@ -23,6 +23,14 @@ class AirQualityTelemetryModule : private concurrency::OSThread, public Protobuf
         setIntervalFromNow(10 * 1000);
         aqi = Adafruit_PM25AQI();
         nodeStatusObserver.observe(&nodeStatus->onNewStatus);
+
+#ifdef PMSA003I_ENABLE_PIN
+        // the PMSA003I sensor uses about 300mW on its own; support powering it off when it's not actively taking
+        // a reading
+        state = State::IDLE;
+#else
+        state = State::ACTIVE;
+#endif
     }
 
   protected:
@@ -42,6 +50,12 @@ class AirQualityTelemetryModule : private concurrency::OSThread, public Protobuf
     bool sendTelemetry(NodeNum dest = NODENUM_BROADCAST, bool wantReplies = false);
 
   private:
+    enum State {
+        IDLE = 0,
+        ACTIVE = 1,
+    };
+
+    State state;
     Adafruit_PM25AQI aqi;
     PM25_AQI_Data data = {0};
     bool firstTime = true;

variants/rak4631/variant.h

@@ -197,6 +197,12 @@ SO GPIO 39/TXEN MAY NOT BE DEFINED FOR SUCCESSFUL OPERATION OF THE SX1262 - TG
 
 */
 
+// configure the SET pin on the RAK12039 sensor board to disable the sensor while not reading
+// air quality telemetry.  PIN_NFC2 doesn't seem to be used anywhere else in the codebase, but if
+// you're having problems with your node behaving weirdly when a RAK12039 board isn't connected,
+// try disabling this.
+#define PMSA003I_ENABLE_PIN PIN_NFC2
+
 #define DETECTION_SENSOR_EN 4
 
 #define USE_SX1262