subtract own radiation

src/main.cpp

@@ -58,6 +58,7 @@ static constexpr uint8_t SDS_RX = D2;
 
 static constexpr uint8_t GEIGER_PIN = D6;
 static constexpr float CONV_FACTOR = 0.008120;
+static constexpr float OWN_BACKGROUND_CPS = 0.2;
 static constexpr unsigned long logging_period_ms = 60000;
 
 ADC_MODE(ADC_VCC);
@@ -114,9 +115,10 @@ void ICACHE_FLASH_ATTR sendValues() {
   float radiationValue = -1;
   if (millis() - geiger_previousMillis > logging_period_ms) {
     cpm = geiger_counts * 60000 / (millis() - geiger_previousMillis);
+    unsigned long constexpr own_cpm = OWN_BACKGROUND_CPS * 60;
     geiger_previousMillis = millis();
     geiger_counts = 0;
-    radiationValue = cpm * CONV_FACTOR;
+    radiationValue = (cpm - own_cpm) * CONV_FACTOR;
 //    Serial.println(cpm);
   } else {
 //    Serial.println("Geiger Counter: no new value");