Test naive bang-bang control algorithm for temperature

src/bus/pwm.c

@@ -102,12 +102,6 @@ void PWM_SetValue(int port, int value)
 
 	n = CLAMP(value, 100, 0) * PWM_CYCLE_TOP / 100.0f;
 
-	Info("Setting duty cycle for %s to %d/%d...",
-		(port == FAN01) ? "FAN01" :
-		(port == FAN02) ? "FAN02" :
-		(port == FAN03) ? "FAN03" :
-		"UNKNOWN", n, PWM_CYCLE_TOP);
-
 	switch (port) {
 	case PD4: OCR1B = n; break;
 	case PD5: OCR1A = n; break;

src/main.c

@@ -6,6 +6,17 @@
 
 #include <avr/interrupt.h>
 
+#define HYSTERESIS 1.0f
+
+// https://en.wikipedia.org/wiki/Bang%E2%80%93bang_control
+// https://support.75f.io/hc/en-us/articles/360044956794-Deadband-and-Hysteresis
+// https://www.elotech.de/fileadmin/user_upload/PID-Regelungsgrundlagen.pdf
+// https://thomasfermi.github.io/Algorithms-for-Automated-Driving/Control/PID.html
+// https://www.ni.com/en/shop/labview/pid-theory-explained.html
+// https://en.wikipedia.org/wiki/Proportional%E2%80%93integral%E2%80%93derivative_controller
+// https://ctms.engin.umich.edu/CTMS/index.php?example=Introduction&section=ControlPID
+// https://www.youtube.com/watch?v=wkfEZmsQqiA&list=PLn8PRpmsu08pQBgjxYFXSsODEF3Jqmm-y
+
 enum state_e
 {
 	S_IDLE,
@@ -121,6 +132,7 @@ static void Update(void)
 {
 	char ch;
 	cmd_t cmd;
+	float terr;
 
 	// Parse serial commands
 	while ((ch = UART_Getc()) >= 0) {
@@ -137,13 +149,48 @@ static void Update(void)
 	// Get latest sensor values
 	FetchSensorValues();
 
-	// Handle state
+	// Two-step (bang-bang) controller testing
+
+	// TODO: Sanity check setpoint!
+	// TODO: Check thermistor for overheating!
+	// TODO: PID control for fan pulse-width modulation?
+
+	// The dead band represents the lower and upper limits
+	// of the error between which the controller doesn’t
+	// react.
+
+	state = S_IDLE;
+	terr = temp - temp_target;
+
+	if (terr < -HYSTERESIS) {
+		state = S_HEAT_UP;
+	}
+
+	if (terr > HYSTERESIS) {
+		state = S_COOL_DOWN;
+	}
+
 	switch (state) {
 	case S_IDLE:
+		MOS_Disable(MOS01);
+		MOS_Disable(MOS02);
+		PWM_SetValue(FAN01, 20);
+		PWM_SetValue(FAN02, 20);
+		PWM_SetValue(FAN03, 20);
 		break;
 	case S_HEAT_UP:
+		MOS_Enable(MOS02);
+		MOS_Disable(MOS01);
+		PWM_SetValue(FAN01, 20);
+		PWM_SetValue(FAN02, 60);
+		PWM_SetValue(FAN03, 60);
 		break;
 	case S_COOL_DOWN:
+		MOS_Enable(MOS01);
+		MOS_Disable(MOS02);
+		PWM_SetValue(FAN01, 60);
+		PWM_SetValue(FAN02, 60);
+		PWM_SetValue(FAN03, 60);
 		break;
 	case S_DEHUMIDIFY:
 		break;
@@ -213,6 +260,11 @@ static void FetchSensorValues(void)
 	Info("T3=%.2fC, TD3=%.2fC, RH3=%.2f%%, NT3=%.2fC", t[2], td[2], rh[2], t[5]);
 	Info("T_AVG=%.2fC, TD_AVG=%.2fC, RH_AVG=%.2f%%", temp, dewp, rhum);
 	Info("T_TAR=%.2fC, TD_TAR=%.2fC", temp_target, dewp_target);
+	Info("STATE=%s", (state == S_IDLE)        ? "S_IDLE"        :
+	                 (state == S_HEAT_UP)     ? "S_HEAT_UP"     :
+	                 (state == S_COOL_DOWN)   ? "S_COOL_DOWN"   :
+	                 (state == S_DEHUMIDIFY)  ? "S_DEHUMIDIFY"  :
+	                 "UNKNOWN");
 }
 
 int main(void)