Use custom ADC interface using AVR flags

src/atmega/Makefile

@@ -27,9 +27,10 @@ CXXFLAGS = $(CFLAGS) -fno-exceptions -fpermissive -std=gnu++11
 LDFLAGS = -Wall -Os -mmcu=$(MCU) -Wl,--gc-sections
 LIBS = -lm
 
-SRCS_CPP = main.cpp moisture.cpp
-HDRS = moisture.h config.h
-OBJS = $(addprefix $(OBJ_DIR)/, $(SRCS_CPP:.cpp=.o))
+SRCS_C = adc.c moisture.c main.c
+#SRCS_CPP = main.cpp
+HDRS = moisture.h config.h adc.h
+OBJS = $(addprefix $(OBJ_DIR)/, $(SRCS_CPP:.cpp=.o) $(SRCS_C:.c=.o))
 
 CORE_C_SRCS = \
 	wiring.c \
@@ -44,7 +45,6 @@ CORE_CPP_SRCS = \
 	Stream.cpp \
 	HardwareSerial.cpp \
 	HardwareSerial0.cpp \
-	main.cpp
 
 CORE_SRCS = $(addprefix $(ARDUINO_CORE_PATH)/, $(CORE_C_SRCS) $(CORE_CPP_SRCS))
 CORE_OBJS = $(patsubst $(ARDUINO_CORE_PATH)/%.c,$(CORE_DIR)/%.o,$(filter %.c,$(CORE_SRCS))) \
@@ -66,6 +66,9 @@ $(ELF_TARGET): $(OBJS) $(CORE_LIB)
 $(CORE_LIB): $(CORE_OBJS)
 	$(AR) rcs $@ $^
 
+$(OBJ_DIR)/%.o: %.c $(HDRS) Makefile
+	$(CC) $(CFLAGS) -c $< -o $@
+
 $(OBJ_DIR)/%.o: %.cpp $(HDRS) Makefile
 	$(CXX) $(CXXFLAGS) -c $< -o $@
 

src/atmega/adc.c

@@ -0,0 +1,27 @@
+#include <stdint.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+void adcInit(void) {
+    // Set reference voltage to AVcc (REFS0 = 1, REFS1 = 0)
+    ADMUX = (1 << REFS0);
+
+    // Enable ADC and set prescaler to 128 (for 16 MHz clock, gives 125 kHz ADC clock)
+    ADCSRA = (1 << ADEN) | (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0);
+}
+
+uint16_t adcRead(uint8_t channel) {
+    // Select ADC pin (A0-A7) by setting MUX bits in ADMUX
+    // Pins A6 and A7 would make an 8 sensor array possible (for large vases).
+    // Achievable only when using the 328p as a DIP, through port C (PC6, PC7)
+    ADMUX = (ADMUX & 0xF8) | (channel & 0x07);
+
+    // Start conversion
+    ADCSRA |= (1 << ADSC);
+
+    // Wait for conversion to complete (ADSC becomes '0' when done)
+    while (ADCSRA & (1 << ADSC));
+
+    // Read ADC (reading order: ADCL --> ADCH)
+    return ADC;
+}

src/atmega/adc.h

@@ -0,0 +1,11 @@
+#ifndef ADC_H
+#define ADC_H
+
+#include <stdint.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+void adcInit(void);
+uint16_t adcRead(uint8_t channel);
+
+#endif

src/atmega/config.h

@@ -1,7 +1,18 @@
 #ifndef CONFIG_H
 #define CONFIG_H
 
-#define MOISTURE_SENSOR_A0 A0
-#define SENSOR_READINGS 3
+#define MOISTURE_SENSOR_A0 PC0
+#define MOISTURE_SENSOR_A1 PC1
+#define MOISTURE_SENSOR_A2 PC2
+#define MOISTURE_SENSOR_A3 PC3
+#define MOISTURE_SENSOR_A4 PC4
+#define MOISTURE_SENSOR_A5 PC5
+// NOTE: PC6 PC7 are not accessible by default on Arduino Uno R3
+// You need to use the ATMega328p on a custom PCB and use pins 1 and 2
+#define MOISTURE_SENSOR_A6 PC6
+#define MOISTURE_SENSOR_A7 PC7
+
+
+#define SENSOR_READINGS 5
 
 #endif

src/atmega/main.c

@@ -1,4 +1,3 @@
-#include <Arduino.h>
 #include <stdint.h>
 #include <stdbool.h>
 #include <avr/sleep.h>
@@ -26,17 +25,19 @@ void enterSleep(void) {
 }
 
 void setup(void) {
-    Serial.begin(9600);
     initMoistureSensor();
     watchdogs();
 }
 
 int main(void) {
+    setup();
+
     while(true) {
+
         if (readSensors) {
             int16_t result = readMoisture();
             if (result != -1) {
-                Serial.println(result);
+                //Serial.println(result);
                 readSensors = false;
             }
         }

src/atmega/moisture.c

@@ -1,10 +1,10 @@
-#include <Arduino.h>
 #include <stdint.h>
 #include <stdbool.h>
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include "moisture.h"
 #include "config.h"
+#include "adc.h"
 
 static int16_t moistureReadingSum = 0;
 static int8_t moistureReadingCount = 0;
@@ -12,7 +12,8 @@ static int8_t moistureReadingCount = 0;
 volatile bool readSensors = false;
 
 void initMoistureSensor(void) {
-    pinMode(MOISTURE_SENSOR_A0, INPUT);
+    DDRC &= ~(1 << MOISTURE_SENSOR_A0); // set as input
+    PORTC &= ~(1 << MOISTURE_SENSOR_A0); //disable pullup
 }
 
 void triggerSensorRead(void) {
@@ -23,13 +24,13 @@ int16_t readMoisture(void) {
     if (!readSensors)
         return -1;
 
-    moistureReadingSum += analogRead(MOISTURE_SENSOR_A0);
+    adcInit();
+    moistureReadingSum += adcRead(MOISTURE_SENSOR_A0);
     moistureReadingCount++;
 
     //TODO: implement variance check (if over a certain variance discard measurements for this cicle)
     if (moistureReadingCount >= SENSOR_READINGS) {
         int16_t average = moistureReadingSum / SENSOR_READINGS;
-        //Serial.println(average);
         moistureReadingSum = 0;
         moistureReadingCount = 0;
         readSensors = false;