Add overheat protection

barista/Makefile

@@ -9,13 +9,20 @@ PROJ=barista
 BUILD=build/$(subst :,.,$(FQBN))
 HEX=$(BUILD)/$(PROJ).ino.hex
 
+SRC=barista.ino \
+    ntc.c \
+    ntc.h \
+    pinout.h \
+    overheat.c \
+    overheat.h
+
 # For host test programs
 CPPFLAGS=-I.
 LIBS=-lm
 
 all: $(HEX)
 
-$(HEX): barista.ino ntc.c ntc.h pinout.h
+$(HEX): $(SRC)
 	arduino-cli compile $(OPTS) -e --fqbn $(FQBN)
 
 upload: $(HEX)
@@ -24,11 +31,14 @@ upload: $(HEX)
 serial:
 	picocom -b 9600 --lower-rts --lower-dtr /dev/ttyUSB0 --imap lfcrlf
 
-test: test_ntc
+test: test_ntc test_overheat
 
 test_ntc: test/test_ntc.o ntc.o
 	gcc $^ -o $@ $(LIBS)
 
+test_overheat: test/test_overheat.o overheat.o
+	gcc $^ -o $@ $(LIBS)
+
 clean:
 	rm -f test/test_ntc.o ntc.o
 

barista/barista.ino

@@ -2,6 +2,7 @@
  * SPDX-License-Identifier: GPL-3.0-or-later */
 
 #include "ntc.h"
+#include "overheat.h"
 #include "pinout.h"
 #include <avr/wdt.h>
 
@@ -23,6 +24,7 @@ enum machine_state {
 	HOT,
 	BREWING,
 	COOLING,
+	PANIC_OVERHEAT,
 };
 
 //int state = SLEEPING;
@@ -83,6 +85,9 @@ struct state {
 	struct btn btn[MAX_BTN];
 	enum buzz_state buzz_state;
 	unsigned long buzz_t0;
+
+	struct overheat overheat;
+	unsigned long overheat_t0;
 } g_st;
 
 int read_input(int pin)
@@ -133,6 +138,8 @@ void proc_ntc(struct state *state, const struct input *input)
 		avg += state->ntc_array_T[i];
 
 	state->ntc_T = avg / MAX_SAMPLES;
+
+	overheat_input(&state->overheat, millis(), state->ntc_T);
 }
 
 void proc_buttons(struct state *state, const struct input *input)
@@ -169,10 +176,16 @@ void proc_buttons(struct state *state, const struct input *input)
 	}
 }
 
+/* In PANIC_OVERHEAT state wait at least TIME_OVERHEAT_COOL and until the
+ * temperature goes below TIME_OVERHEAT_TEMP before doing anything. */
+#define TIME_OVERHEAT_COOL  10000 /* ms */
+#define TIME_OVERHEAT_TEMP  40.0  /* °C */
+
 int red_min = 50;
 int red_state = red_min;
 unsigned long brewing_time     =  3000UL; /* 3 seconds */
 unsigned long cooling_time     =  3000UL; /* 3 seconds */
+unsigned long overheat_time    = 10000UL; /* 10 seconds */
 unsigned long max_heating_time = 60000UL; /* 60 seconds */
 unsigned long max_idle_time    = 10000UL; /* 10 seconds */
 
@@ -192,6 +205,13 @@ void proc_machine(struct state *st)
 	Serial.print(temp);
 	Serial.println(" C");
 
+	/* If the machine is overheating */
+	if (overheat_panic(&st->overheat)) {
+		st->mstate = PANIC_OVERHEAT;
+		st->overheat_t0 = millis();
+		Serial.println("PANIC OVERHEATING");
+	}
+
 	/* Pressing ON cancels any operation */
 	if (st->mstate != SLEEPING && on) {
 		st->mstate = SLEEPING;
@@ -238,6 +258,13 @@ void proc_machine(struct state *st)
 			st->heating_t0 = millis();
 			Serial.println("heating");
 		}
+	} else if (st->mstate == PANIC_OVERHEAT) {
+		/* Wait until it cools down and enough time has passed */
+		if (st->ntc_T < TIME_OVERHEAT_TEMP &&
+				millis() - st->overheat_t0 > TIME_OVERHEAT_COOL) {
+			st->mstate = SLEEPING;
+			Serial.println("sleeping");
+		}
 	}
 }
 
@@ -278,18 +305,21 @@ output_leds(const struct state *st)
 		if (r >= 255)
 			r = 0;
 		else
-			r += 3;
+			r += 5;
 	} else if (st->mstate == HOT) {
 		setled(PIN_LED_RED, 0);
 		setled(PIN_LED_GREEN, 1);
 		r = 0;
+	} else if (st->mstate == PANIC_OVERHEAT) {
+		setled(PIN_LED_RED, 1);
+		setled(PIN_LED_GREEN, 0);
 	} else if (st->mstate == BREWING) {
 		setled(PIN_LED_RED, 0);
 		analogWrite(PIN_LED_GREEN, g);
 		if (g >= 255)
 			g = 0;
 		else
-			g += 3;
+			g += 5;
 	} else {
 		setled(PIN_LED_RED, 0);
 		setled(PIN_LED_GREEN, 0);
@@ -343,6 +373,8 @@ void setup()
 	relay(PIN_HEAT, OFF);
 	relay(PIN_PUMP, OFF);
 
+	overheat_init(&g_st.overheat);
+
 	Serial.println("Ready");
 	wdt_enable(WDTO_250MS);
 }

barista/overheat.c

@@ -0,0 +1,52 @@
+/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include "overheat.h"
+#include <string.h>
+
+void
+overheat_init(struct overheat *o)
+{
+	memset(o, 0, sizeof(struct overheat));
+}
+
+void
+overheat_input(struct overheat *o, unsigned long t_ms, float temp)
+{
+	unsigned long delta = t_ms - o->last_time;
+
+	if (delta < OVH_INTERVAL)
+		return;
+
+	o->temp[o->next++] = temp;
+	if (o->next >= OVH_NSAMPLES)
+		o->next = 0;
+	if (o->n < OVH_NSAMPLES)
+		o->n++;
+
+	/* Recompute state */
+	float tmin = 10000.0, tmax = 0.0;
+	for (int i = 0; i < o->n; i++) {
+		if (o->temp[i] < tmin)
+			tmin = o->temp[i];
+		if (o->temp[i] > tmax)
+			tmax = o->temp[i];
+	}
+
+	o->delta = tmax - tmin;
+}
+
+float
+overheat_delta(struct overheat *o)
+{
+	return o->delta;
+}
+
+int
+overheat_panic(struct overheat *o)
+{
+	if (o->delta > OVH_THRESHOLD)
+		return 1;
+	else
+		return 0;
+}

barista/overheat.h

@@ -0,0 +1,32 @@
+/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#ifndef BARISTA_OVERHEAT_H
+#define BARISTA_OVERHEAT_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define OVH_NSAMPLES	20
+#define OVH_INTERVAL	200 /* ms */
+#define OVH_THRESHOLD	2.0 /* °C */
+
+struct overheat {
+	unsigned long last_time;
+	float temp[OVH_NSAMPLES];
+	int next;
+	int n;
+	float delta;
+};
+
+void overheat_init(struct overheat *o);
+void overheat_input(struct overheat *o, unsigned long t_ms, float temp);
+float overheat_delta(struct overheat *o);
+int overheat_panic(struct overheat *o);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* BARISTA_OVERHEAT_H */

barista/test/test_ntc.c

@@ -1,3 +1,6 @@
+/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
 #include <stdio.h>
 #include "ntc.h"
 

barista/test/test_overheat.c

@@ -0,0 +1,36 @@
+/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <stdio.h>
+#include "overheat.h"
+
+/* Read a CSV from the stdin in the format
+ * <time_in_seconds> <state> <temp_in_C>
+ * skipping the first row (header).
+ *
+ * Outputs overheat state. */
+
+#define MAX_LINE 1024
+
+int main(void)
+{
+	char buf[MAX_LINE];
+	fgets(buf, MAX_LINE, stdin);
+
+	float t, temp;
+	int st;
+
+	struct overheat ovh;
+	overheat_init(&ovh);
+
+	while (scanf("%f %d %f", &t, &st, &temp) == 3) {
+
+		overheat_input(&ovh, t * 1000.0, temp);
+		float delta = overheat_delta(&ovh);
+		int panic = overheat_panic(&ovh);
+
+		printf("%.3f %d %.2f %.1f %s\n", t, st, temp, delta, panic ? "PANIC" : "OK");
+	}
+
+	return 0;
+}