Add temperature data with overheat protection

Prevents a hang from keeping the heater or pump relays always on, which
could cause the thermal fuses to burn or the pump to empty the deposit
and then burn as well.

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

@@ -2,7 +2,9 @@
  * SPDX-License-Identifier: GPL-3.0-or-later */
 
 #include "ntc.h"
+#include "overheat.h"
 #include "pinout.h"
+#include <avr/wdt.h>
 
 enum logic {
 	ON = 1,
@@ -22,6 +24,7 @@ enum machine_state {
 	HOT,
 	BREWING,
 	COOLING,
+	PANIC_OVERHEAT,
 };
 
 //int state = SLEEPING;
@@ -74,6 +77,7 @@ struct state {
 	unsigned long hot_t0;
 
 	int ntc_i; /* Next available place */
+	int ntc_n; /* Samples in array */
 	float ntc_R;
 	float ntc_last_T;
 	float ntc_array_T[MAX_SAMPLES];
@@ -82,6 +86,9 @@ 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)
@@ -126,12 +133,16 @@ void proc_ntc(struct state *state, const struct input *input)
 	state->ntc_array_T[state->ntc_i++] = state->ntc_last_T;
 	if (state->ntc_i >= MAX_SAMPLES)
 		state->ntc_i = 0;
+	if (state->ntc_n < MAX_SAMPLES)
+		state->ntc_n++;
 
 	float avg = 0;
-	for (int i = 0; i < MAX_SAMPLES; i++)
+	for (int i = 0; i < state->ntc_n; i++)
 		avg += state->ntc_array_T[i];
 
-	state->ntc_T = avg / MAX_SAMPLES;
+	state->ntc_T = avg / state->ntc_n;
+
+	overheat_input(&state->overheat, millis(), state->ntc_T);
 }
 
 void proc_buttons(struct state *state, const struct input *input)
@@ -168,10 +179,16 @@ 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 brewing_time     =  3000UL; /* 3 seconds */
-unsigned long cooling_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 */
 
@@ -191,6 +208,13 @@ 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;
@@ -237,6 +261,13 @@ 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");
+		}
 	}
 }
 
@@ -277,18 +308,21 @@ 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);
@@ -326,6 +360,7 @@ void do_output(const struct state *st)
 
 void setup()
 {
+	wdt_disable();
 	Serial.begin(9600);
 	Serial.println("Booting");
 
@@ -341,7 +376,10 @@ void setup()
 	relay(PIN_HEAT, OFF);
 	relay(PIN_PUMP, OFF);
 
+	overheat_init(&g_st.overheat);
+
 	Serial.println("Ready");
+	wdt_enable(WDTO_250MS);
 }
 
 void loop()
@@ -351,4 +389,5 @@ void loop()
 	do_output(&g_st);
 
 	delay(5);
+	wdt_reset();
 }

barista/data/overheat-cutoff.csv

@@ -0,0 +1,959 @@
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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;
+}