Extracts soil reading to SoilMonitor

code/parasite/lib/parasite/parasite/adc.cpp

@@ -0,0 +1,48 @@
+#include "parasite/adc.h"
+
+#include <Arduino.h>
+
+#include <algorithm>
+
+namespace parasite {
+namespace {
+// Resultion in bits. ADC read values will be mapped to [0, 2^reference].
+constexpr int kResolution = 10;
+
+/*
+ * Battery monitoring
+ */
+// Use the internal 0.6 reference with a gain of 1/2.
+// This lets us read values in the range [0, 1.2V].
+constexpr eAnalogReference kBattADCReference = AR_INTERNAL_1_2;
+constexpr double kMaxVoltage = 1.2;
+// How many samples will be averaged out.
+constexpr uint32_t kOversampling = 32;
+// Voltage divider.
+constexpr double kBattDividerR1 = 1470;
+constexpr double kBattDividerR2 = 470;
+constexpr double kBattDividerFactor =
+    (kBattDividerR1 + kBattDividerR2) / kBattDividerR2;
+}  // namespace
+
+double BatteryMonitor::Read() {
+  analogOversampling(kOversampling);
+  analogReference(kBattADCReference);
+  int batt_val = analogRead(pin_);
+  double v_in = kMaxVoltage * batt_val / (1 << kResolution);
+  return kBattDividerFactor * v_in;
+}
+
+soil_reading_t SoilMonitor::Read() {
+  analogOversampling(kOversampling);
+  // Set up the analog reference to be VDD. This allows us to cancel out
+  // the effect of the battery discharge across time, since the RC circuit
+  // also depends linearly on VDD.
+  analogReference(AR_VDD4);
+  int raw = analogRead(pin_);
+  double percentage =
+      static_cast<double>(raw - air_val_) / (water_val_ - air_val_);
+  return {raw, std::max(0.0, std::min(1.0, percentage))};
+}
+
+}  // namespace parasite

code/parasite/lib/parasite/parasite/adc.h

@@ -0,0 +1,35 @@
+#ifndef _PARASITE_ADC_H_
+#define _PARASITE_ADC_H_
+
+namespace parasite {
+
+class BatteryMonitor {
+ public:
+  explicit BatteryMonitor(int pin) : pin_(pin) {}
+  double Read();
+
+ private:
+  const int pin_;
+};
+
+struct soil_reading_t {
+  int raw;
+  double parcent;
+};
+
+class SoilMonitor {
+ public:
+  explicit SoilMonitor(int air_val, int water_val, int pin)
+      : air_val_(air_val), water_val_(water_val), pin_(pin) {}
+
+  soil_reading_t Read();
+
+ private:
+  // Referencce values for estimating the soil moisture percentage.
+  const int air_val_, water_val_;
+
+  // Pin the analog signal is connected to.
+  const int pin_;
+};
+}  // namespace parasite
+#endif  // _PARASITE_ADC_H_

code/parasite/src/main.cpp

@@ -1,8 +1,8 @@
 #include <Arduino.h>
 
 #include <cstring>
-#include <vector>
 
+#include "parasite/adc.h"
 #include "parasite/ble.h"
 #include "parasite/ble_advertisement_data.h"
 #include "parasite/pwm.h"
@@ -10,22 +10,25 @@
 constexpr int kLED1Pin = 17;
 constexpr int kLED2Pin = 18;
 constexpr int kPWMPin = 19;
-constexpr int kSensAnalogPin = 4;  // AIN2
+constexpr int kSoilAnalogPin = 4;  // AIN2
 constexpr int kBattAnalogPin = 3;  // AIN3
 constexpr int kDischargeEnablePin = 16;
 constexpr double kPWMFrequency = 500000;
-
-constexpr double kBattDividerR1 = 1470;
-constexpr double kBattDividerR2 = 470;
-constexpr double kBattDividerFactor = (kBattDividerR1 + kBattDividerR2) / kBattDividerR2;
+constexpr int kSoilMonitorAirVal = 680;
+constexpr int kSoilMonitorWaterVal = 60;
 
 const parasite::MACAddr kMACAddr = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06};
 parasite::BLEAdvertiser advertiser(kMACAddr);
 
-void updateAdvertisingData(parasite::BLEAdvertiser *advertiser,
-                           int moisture_level) {
+parasite::BatteryMonitor batt_monitor(kBattAnalogPin);
+parasite::SoilMonitor soil_monitor(kSoilMonitorAirVal, kSoilMonitorWaterVal,
+                                   kSoilAnalogPin);
+
+void updateAdvertisingData(parasite::BLEAdvertiser* advertiser,
+                           const parasite::soil_reading_t& soil_reading) {
   parasite::BLEAdvertisementData data;
-  data.SetRawSoilMoisture(moisture_level);
+
+  data.SetRawSoilMoisture(soil_reading.raw);
 
   advertiser->SetData(data);
 
@@ -48,25 +51,16 @@ void setup() {
 }
 
 void loop() {
-  // With a gain of 1/2, we can read the range of [0, 1.2V].
-  // I'm using a voltage divider with R1 = 1470, R2 470, so
-  // We can read 0 - ~5V.
-  // This seems to be working okay, but I need to investigate if making it
-  // stiffer (lower R1 and R2) work better.
-  analogOversampling(32);
-  analogReference(AR_INTERNAL_1_2);
-  int batt_val = analogRead(kBattAnalogPin);
-  double v_in = 1.2 * batt_val / (1<<10);
-  double batt_voltage = kBattDividerFactor * v_in;
-  Serial.printf("Batt val: %d, voltage: %f\n", batt_val, batt_voltage);
+  double batt_voltage = batt_monitor.Read();
+  Serial.printf("Batt voltage: %f\n", batt_voltage);
+
+  parasite::soil_reading_t soil_reading = soil_monitor.Read();
+  Serial.printf("Moisture val: %d, %f%%\n", soil_reading.raw,
+                100 * soil_reading.parcent);
 
-  // We setup the analog reference to be VDD. This allows us to cancel out
-  // the effect of the battery discharge across time, since the RC circuit
-  // also depends linearly on VDD.
-  analogReference(AR_VDD4);
-  int sens_val = analogRead(kSensAnalogPin);
-  // Serial.printf("Moisture val: %d\n", sens_val);
   digitalToggle(kLED1Pin);
-  updateAdvertisingData(&advertiser, sens_val);
+
+  updateAdvertisingData(&advertiser, soil_reading);
+
   delay(500);
 }