   rf95.setModemConfig(RH_RF95::Bw500Cr45Sf128);
   rf95.setTxPower(10, false);
 
+  pinMode(PIN_SENSOR_VCC, OUTPUT);
+  // Start with no volts to the sensors using this power source.
+  digitalWrite(PIN_SENSOR_VCC, LOW);
+
   ads.begin();
 }
 


#define RF95_FREQ 868.0

#define PIN_SENSOR_LIGHT A0
#define PIN_SENSOR_SOIL A2



uint16_t readSolarVolts() {
  // Voltage divider to reduce the maximum to 2V.
  // 8V -> 2V
  // Solar panel --- 300K --- | --- 100K --- GND
  int16_t val = ads.readADC_SingleEnded(2);
  // Calibration:
  // 1000mV = 268, 2000mV = 537, 3000mV = 805... 
