diff --git a/src/main.c b/src/main.c
index 78a87a5..a33ef5d 100644
--- a/src/main.c
+++ b/src/main.c
@@ -6,17 +6,31 @@
 
 #include <avr/interrupt.h>
 
+// TODO: Implement primary state machine for update loop.
+// TODO: Migrate to ATMega 1284P-PU for 2nd 16-bit timer.
+// TODO: Keep persistent TEMP and DEWP targets in EEPROM.
+// TODO: Check thermistor conversion results /w thermometer.
 // TODO: Implement optional CRC8 sensor measurement check.
-// TODO: Either implement software PWM for the FAN03 timer
-// (which will be quite complicated) or pick a chip with
-// more than two 16-bit PWM outputs like the ATmega328PB.
-// https://www.mikrocontroller.net/articles/Soft-PWM
-// TODO: Check if FAN02 is receiving the right frequency.
+// TODO: Use 18.432MHz quarz crystal, burn required fuses.
 // TODO: Write an improved command parser (low priority).
 // TODO: Proper error handling and recovery (after testing).
 
+enum state_e
+{
+	S_IDLE,
+	S_HEAT_UP,
+	S_COOL_DOWN,
+	S_DEHUMIDIFY
+};
+
+static enum state_e state;
+static float temp, temp_target;
+static float dewp, dewp_target;
+
 static int Init(void)
 {
+	state = S_IDLE;
+
 	// MOSFETS control things like the heating element
 	// so they are the highest priority to initialize
 	// to a default state via MOS_Init().
@@ -96,32 +110,46 @@ static int Init(void)
 
 static void Update(void)
 {
-	float temp[3], rh[3];
+	float t[3], rh[3];
 	float adct[3];
 
 	Info("Reading sensor values...");
 
 	I2C_SetChannel(AHT01);
-	I2C_AHT20_Read(&temp[0], &rh[0]);
+	I2C_AHT20_Read(&t[0], &rh[0]);
 
 	I2C_SetChannel(AHT02);
-	I2C_AHT20_Read(&temp[1], &rh[1]);
+	I2C_AHT20_Read(&t[1], &rh[1]);
 
 	I2C_SetChannel(AHT03);
-	I2C_AHT20_Read(&temp[2], &rh[2]);
+	I2C_AHT20_Read(&t[2], &rh[2]);
 
 	adct[0] = I2C_ADS1115_ReadThermistor(ADS01);
 	adct[1] = I2C_ADS1115_ReadThermistor(ADS02);
 	adct[2] = I2C_ADS1115_ReadThermistor(ADS03);
 
-	Info("TEMP1=%.2fC, RH1=%.2f%% ADCT1=%.2fC", temp[0], rh[0], adct[0]);
-	Info("TEMP2=%.2fC, RH2=%.2f%% ADCT2=%.2fC", temp[1], rh[1], adct[1]);
-	Info("TEMP3=%.2fC, RH3=%.2f%% ADCT3=%.2fC", temp[2], rh[2], adct[2]);
+	Info("T1=%.2fC, RH1=%.2f%%, ADCT1=%.2fC", t[0], rh[0], adct[0]);
+	Info("T2=%.2fC, RH2=%.2f%%, ADCT2=%.2fC", t[1], rh[1], adct[1]);
+	Info("T3=%.2fC, RH3=%.2f%%, ADCT3=%.2fC", t[2], rh[2], adct[2]);
 
 	// TODO: Implement state machine
+	// TODO: Handle serial commands
 
-	// Inputs: TEMP, DEWP
-	// States: IDLE, DEHUMIDIFY, HEATUP, COOLDOWN
+	switch (state) {
+	case S_IDLE:
+		break;
+	case S_HEAT_UP:
+		break;
+	case S_COOL_DOWN:
+		break;
+	case S_DEHUMIDIFY:
+		break;
+	}
+
+	UNUSED(temp);
+	UNUSED(dewp);
+	UNUSED(temp_target);
+	UNUSED(dewp_target);
 }
 
 int main(void)