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Add NTC coefficients to measure celsius

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This commit is contained in:
Rodrigo Arias Mallo 2025-10-13 21:09:06 +02:00
parent 695aa4b3c2
commit 9c114b136a
8 changed files with 329 additions and 173 deletions
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2
barista/.gitignore vendored
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@ -1 +1,3 @@
build/ build/
test_ntc
*.o

22
barista/Makefile
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@ -1,13 +1,21 @@
# Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
# SPDX-License-Identifier: GPL-3.0-or-later
PORT=/dev/ttyUSB0 PORT=/dev/ttyUSB0
FQBN=arduino:avr:atmega328bb FQBN=arduino:avr:atmega328bb
OPTS=--no-color --log-level=info -v OPTS=--no-color --log-level=info
#OPTS+=-v
PROJ=barista PROJ=barista
BUILD=build/$(subst :,.,$(FQBN)) BUILD=build/$(subst :,.,$(FQBN))
HEX=$(BUILD)/$(PROJ).ino.hex HEX=$(BUILD)/$(PROJ).ino.hex
# For host test programs
CPPFLAGS=-I.
LIBS=-lm
all: $(HEX) all: $(HEX)
$(HEX): barista.ino $(HEX): barista.ino ntc.c ntc.h pinout.h
arduino-cli compile $(OPTS) -e --fqbn $(FQBN) arduino-cli compile $(OPTS) -e --fqbn $(FQBN)
upload: $(HEX) upload: $(HEX)
@ -15,3 +23,13 @@ upload: $(HEX)
serial: serial:
picocom -b 115200 --lower-rts --lower-dtr /dev/ttyUSB0 --imap lfcrlf picocom -b 115200 --lower-rts --lower-dtr /dev/ttyUSB0 --imap lfcrlf
test: test_ntc
test_ntc: test/test_ntc.o ntc.o
gcc $^ -o $@ $(LIBS)
clean:
rm -f test/test_ntc.o ntc.o
.PHONY: test all clean

114
barista/barista.ino
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@ -1,64 +1,8 @@
/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com> /* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
* SPDX-License-Identifier: GPL-3.0-or-later */ * SPDX-License-Identifier: GPL-3.0-or-later */
/* #include "ntc.h"
* ATmega328p #include "pinout.h"
* +---------+
* (PCINT14/RESET) PC6 -|1 \_/ 28|- PC5 (ADC5/SCL/PCINT13)
* (PCINT16/RXD) PD0 -|2 27|- PC4 (ADC4/SDA/PCINT12)
* (PCINT17/TXD) PD1 -|3 26|- PC3 (ADC3/PCINT11)
* (PCINT18/INT0) PD2 -|4 25|- PC2 (ADC2/PCINT10)
* (PCINT19/OC2B/INT1) PD3 -|5 24|- PC1 (ADC1/PCINT9)
* (PCINT20/XCK/T0) PD4 -|6 23|- PC0 (ADC0/PCINT8)
* VCC -|7 22|- GND
* GND -|8 21|- AREF
* (PCINT6/XTAL1/TOSC1) PB6 -|9 20|- AVCC
* (PCINT7/XTAL2/TOSC2) PB7 -|10 19|- PB5 (SCK/PCINT5)
* (PCINT21/OC0B/T1) PD5 -|11 18|- PB4 (MISO/PCINT4)
* (PCINT22/OC0A/AIN0) PD6 -|12 17|- PB3 (MOSI/OC2A/PCINT3)
* (PCINT23/AIN1) PD7 -|13 16|- PB2 (SS/OC1B/PCINT2)
* (PCINT0/CLKO/ICP1) PB0 -|14 15|- PB1 (OC1A/PCINT1)
* +---------+
*
*
* ATMEL ATMEGA8 & 168 / ARDUINO
*
* +-\/-+
* PC6 1| |28 PC5 (AI 5)
* (D 0) PD0 2| |27 PC4 (AI 4)
* (D 1) PD1 3| |26 PC3 (AI 3)
* (D 2) PD2 4| |25 PC2 (AI 2)
* PWM+ (D 3) PD3 5| |24 PC1 (AI 1)
* (D 4) PD4 6| |23 PC0 (AI 0)
* VCC 7| |22 GND
* GND 8| |21 AREF
* PB6 9| |20 AVCC
* PB7 10| |19 PB5 (D 13)
* PWM+ (D 5) PD5 11| |18 PB4 (D 12)
* PWM+ (D 6) PD6 12| |17 PB3 (D 11) PWM
* (D 7) PD7 13| |16 PB2 (D 10) PWM
* (D 8) PB0 14| |15 PB1 (D 9) PWM
* +----+
*
*
*/
enum pinout {
/* Inputs */
PIN_POWER_ON = 8,
PIN_HOT = 9,
//PIN_FLOW = PIN_D5,
/* Outputs */
PIN_LED_GREEN = 5,
PIN_LED_RED = 6,
PIN_HEAT = 7,
PIN_PUMP = 12,
PIN_BUZZ = 10,
/* Analog */
PIN_NTC = PIN_A0,
};
enum logic { enum logic {
ON = 1, ON = 1,
@ -66,8 +10,8 @@ enum logic {
}; };
#define DEBOUNCE_TIME 20L /* ms */ #define DEBOUNCE_TIME 20L /* ms */
#define TEMP_MIN 600 #define TEMP_MIN 80.0f
#define TEMP_MAX 700 #define TEMP_MAX 90.0f
#define LED_MIN_VALUE 0 #define LED_MIN_VALUE 0
@ -114,6 +58,10 @@ int button_state[MAX_BUTTON];
unsigned long button_press_t0[MAX_BUTTON]; unsigned long button_press_t0[MAX_BUTTON];
unsigned long button_release_t0[MAX_BUTTON]; unsigned long button_release_t0[MAX_BUTTON];
float ntc_R;
float ntc_T;
int read_input(int pin) int read_input(int pin)
{ {
return !digitalRead(pin); return !digitalRead(pin);
@ -170,6 +118,13 @@ void update_buttons()
} }
} }
void update_ntc()
{
int Vo = analogRead(PIN_NTC);
ntc_R = ntc_resistance(Vo);
ntc_T = ntc_temp(ntc_R);
}
int red_min = 50; int red_min = 50;
int red_state = red_min; int red_state = red_min;
unsigned long brewing_time = 3000UL; /* 3 seconds */ unsigned long brewing_time = 3000UL; /* 3 seconds */
@ -274,11 +229,25 @@ update_leds()
} }
} }
/* Return the temperature in celsisus */
float
measure_temp()
{
int Vo = analogRead(PIN_NTC);
float c1 = 1.009249522e-03, c2 = 2.378405444e-04, c3 = 2.019202697e-07;
float R1 = 10e3; /* 10 kOhm resistor */
float R2 = R1 * (1023.0 / (float)Vo - 1.0);
float logR2 = log(R2);
float T = (1.0 / (c1 + c2*logR2 + c3*logR2*logR2*logR2));
float Tc = T - 273.15;
return Tc;
}
void void
update_heater() update_heater()
{ {
if (state == HEATING || state == HOT || state == BREWING) { if (state == HEATING || state == HOT || state == BREWING) {
int temp = analogRead(PIN_NTC); int temp = measure_temp();
if (temp < TEMP_MIN) if (temp < TEMP_MIN)
relay(PIN_HEAT, ON); relay(PIN_HEAT, ON);
else if (temp > TEMP_MAX) else if (temp > TEMP_MAX)
@ -318,6 +287,20 @@ update_buzz()
} }
} }
void inputs()
{
update_buttons();
update_ntc();
}
void outputs()
{
update_leds();
update_heater();
update_pump();
update_buzz();
}
void setup() void setup()
{ {
Serial.begin(9600); Serial.begin(9600);
@ -340,12 +323,9 @@ void setup()
void loop() void loop()
{ {
//Serial.println("Looping..."); inputs();
update_buttons();
progress(); progress();
update_leds(); outputs();
update_heater();
update_pump();
update_buzz();
delay(5); delay(5);
} }

44
barista/ntc.c Normal file
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@ -0,0 +1,44 @@
/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
* SPDX-License-Identifier: GPL-3.0-or-later */
#include <math.h>
/* Steinhart-Hart Thermistor Coefficients, used to convert resistance into
* temperature.
*
* The current NTC sensor has 102kOhm at 24C but I don't know the specific
* model, so the coefficients are computed for this NTC sensor instead:
* https://www.tme.eu/Document/f9d2f5e38227fc1c7d979e546ff51768/NTCM-100K-B3950.pdf
*
* The table seems to match what I would expect. Their R2 resistor is 6.8 kOhm,
* which yields a cuttof temperature of around 98.5 C at exactly half voltage
* (where the ADC would have more precision).
*
* In any case, we can calibrate the original NTC sensor by taking three
* temperature points. See:
* https://www.thinksrs.com/downloads/programs/therm%20calc/ntccalibrator/ntccalculator.html
*/
#define C1 0.7740577674e-3
#define C2 2.073449619e-4
#define C3 1.263502259e-7
/* Return the temperature in celsisus */
float
ntc_temp(float R)
{
/* Computing the log is slow, we may want to build a table */
float logR = log(R);
float T = (1.0 / (C1 + C2*logR + C3*logR*logR*logR));
float Tc = T - 273.15;
return Tc;
}
/* Return resistance in Ohms */
float
ntc_resistance(int Vo)
{
float R1 = 6.8e3; /* Resistor for voltage divider */
float R2 = R1 * (1023.0 / (float)Vo - 1.0);
return R2;
}

18
barista/ntc.h Normal file
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@ -0,0 +1,18 @@
/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
* SPDX-License-Identifier: GPL-3.0-or-later */
#ifndef BARISTA_NTC_H
#define BARISTA_NTC_H
#ifdef __cplusplus
extern "C" {
#endif
float ntc_resistance(int Vo);
float ntc_temp(float omhs);
#ifdef __cplusplus
}
#endif
#endif /* BARISTA_NTC_H */

78
barista/pinout.h Normal file
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@ -0,0 +1,78 @@
/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
* SPDX-License-Identifier: GPL-3.0-or-later */
#ifndef BARISTA_PINOUT_H
#define BARISTA_PINOUT_H
#include <Arduino.h>
#ifdef __cplusplus
extern "C" {
#endif
/*
* ATmega328p
* +---------+
* (PCINT14/RESET) PC6 -|1 \_/ 28|- PC5 (ADC5/SCL/PCINT13)
* (PCINT16/RXD) PD0 -|2 27|- PC4 (ADC4/SDA/PCINT12)
* (PCINT17/TXD) PD1 -|3 26|- PC3 (ADC3/PCINT11)
* (PCINT18/INT0) PD2 -|4 25|- PC2 (ADC2/PCINT10)
* (PCINT19/OC2B/INT1) PD3 -|5 24|- PC1 (ADC1/PCINT9)
* (PCINT20/XCK/T0) PD4 -|6 23|- PC0 (ADC0/PCINT8)
* VCC -|7 22|- GND
* GND -|8 21|- AREF
* (PCINT6/XTAL1/TOSC1) PB6 -|9 20|- AVCC
* (PCINT7/XTAL2/TOSC2) PB7 -|10 19|- PB5 (SCK/PCINT5)
* (PCINT21/OC0B/T1) PD5 -|11 18|- PB4 (MISO/PCINT4)
* (PCINT22/OC0A/AIN0) PD6 -|12 17|- PB3 (MOSI/OC2A/PCINT3)
* (PCINT23/AIN1) PD7 -|13 16|- PB2 (SS/OC1B/PCINT2)
* (PCINT0/CLKO/ICP1) PB0 -|14 15|- PB1 (OC1A/PCINT1)
* +---------+
*
*
* ATMEL ATMEGA8 & 168 / ARDUINO
*
* +-\/-+
* PC6 1| |28 PC5 (AI 5)
* (D 0) PD0 2| |27 PC4 (AI 4)
* (D 1) PD1 3| |26 PC3 (AI 3)
* (D 2) PD2 4| |25 PC2 (AI 2)
* PWM+ (D 3) PD3 5| |24 PC1 (AI 1)
* (D 4) PD4 6| |23 PC0 (AI 0)
* VCC 7| |22 GND
* GND 8| |21 AREF
* PB6 9| |20 AVCC
* PB7 10| |19 PB5 (D 13)
* PWM+ (D 5) PD5 11| |18 PB4 (D 12)
* PWM+ (D 6) PD6 12| |17 PB3 (D 11) PWM
* (D 7) PD7 13| |16 PB2 (D 10) PWM
* (D 8) PB0 14| |15 PB1 (D 9) PWM
* +----+
*
*
*/
enum pinout {
/* Inputs */
PIN_POWER_ON = 8,
PIN_HOT = 9,
//PIN_FLOW = PIN_D5,
/* Outputs */
PIN_LED_GREEN = 5,
PIN_LED_RED = 6,
PIN_HEAT = 7,
PIN_PUMP = 12,
PIN_BUZZ = 10,
/* Analog */
PIN_NTC = PIN_A0,
};
#ifdef __cplusplus
}
#endif
#endif /* BARISTA_PINOUT_H */

1
barista/test/Makefile Normal file
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test_ntc: test_ntc.o ../ntc.c

15
barista/test/test_ntc.c Normal file
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@ -0,0 +1,15 @@
#include <stdio.h>
#include "ntc.h"
int main(void)
{
for (int i = 0; i <= 1023; i++) {
float R = ntc_resistance(i);
float T = ntc_temp(R);
if (T < 96.0 || T > 100.2)
continue;
printf("%6d %12.1f Ohm %12.1f C\n", i, R, T);
}
return 0;
}