fix pm low power reading

1 files changed, 16 insertions, 5 deletions

diff --git a/pm.h b/pm.h
index 9c8a508..4bfc10c 100644
--- a/pm.h
+++ b/pm.h
@@ -19,11 +19,13 @@ private:
   uint8_t auto_clean_days;
   unsigned long last_measurment_millis;
   unsigned long read_interval_millis;
+  bool awake;
 public:
   PM(uint8_t acd=4, unsigned long ri=30000) :
     auto_clean_days(acd),
     last_measurment_millis(0),
-    read_interval_millis(ri)
+    read_interval_millis(ri),
+    awake(false)
   {}
 
   void start() {
@@ -47,6 +49,8 @@ public:
     if (ret < 0) {
       Serial.print("PM starting measurement error\n");
     }
+
+    awake=true;
   }
 
   bool dataReady() {
@@ -55,13 +59,19 @@ public:
 
     // have we read recently?
     unsigned long now=millis();
-    // that first check is in case of overflow & rollover
-    if (now > last_measurment_millis && (now - last_measurment_millis) < read_interval_millis) {
+    if (
+        last_measurment_millis > 0 && // have we measured once at least?
+        now > last_measurment_millis && // has there been no overflow & rollover?
+        (now - last_measurment_millis) < read_interval_millis // is it too soon?
+        ) {
       return false;
     }
 
-    sps30_wake_up();
-    sps30_start_measurement();
+    if (!awake) {
+      sps30_wake_up();
+      sps30_start_measurement();
+      awake=true;
+    }
 
     ret = sps30_read_data_ready(&data_ready);
     if (ret < 0) {
@@ -90,5 +100,6 @@ public:
     last_measurment_millis = millis();
     sps30_stop_measurement();
     sps30_sleep();
+    awake=false;
   }
 };