Automotive dashboard display

Projects General Guidance
1

Here is code for an automotive display - so far only AFR / Lambda and RPM. Plan to include GPS speed & odo & running fuel consumption, rpm based on actual scoped frequency from an aftermarket ecu, narrowband AFR formula courtesy of Google. Criticism, comments and improvements welcome.

#include <LiquidCrystal.h>

// ---------------- LCD ----------------
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

// ---------------- PINS ----------------
const byte RPM_PIN = 2;   // ECU RPM output (INT0)
const int afrPin = A0;    // AFR analog input

// ---------------- RPM ----------------
volatile unsigned long lastPulseMicros = 0;
volatile unsigned long periodMicros = 0;
volatile bool newPeriod = false;
unsigned int rpm = 0;
unsigned long lastRPMUpdate = 0;
const unsigned long RPM_TIMEOUT = 300000; // 300 ms no pulses → RPM = 0
const unsigned long LCD_REFRESH = 200; // ms (5 Hz)
unsigned long lastLCDUpdate = 0;
unsigned int lastDisplayedRPM = 65535;
// ---------------- AFR / Lambda ----------------
float afr = 14.7;
float lambda = 1.0;

// ---------------- Warm-up ----------------
const unsigned long WARMUP_TIME = 180000;  // 3 minutes
unsigned long startMillis;

void rpmISR() {
  unsigned long now = micros();
  periodMicros = now - lastPulseMicros;
  lastPulseMicros = now;
  newPeriod = true;
}

void setup() {
  lcd.begin(16, 2);
  lcd.clear();

  lcd.setCursor(0, 0);
  lcd.print("RPM:");

  lcd.setCursor(0, 1);
  lcd.print("AFR:");
  lcd.setCursor(10, 1);
  lcd.print("L:");

  pinMode(RPM_PIN, INPUT);
  attachInterrupt(digitalPinToInterrupt(RPM_PIN), rpmISR, FALLING);

  startMillis = millis();
}

void loop() {
  unsigned long nowMillis = millis();

  // -------- RPM FROM FREQUENCY --------
  if (newPeriod) {
    noInterrupts();
    unsigned long p = periodMicros;
    newPeriod = false;
    interrupts();

    if (p > 0) {
      float frequency = 1000000.0 / p;   // Hz
      rpm = (unsigned int)(frequency * 40.0);
      lastRPMUpdate = micros();
    }
  }

  // RPM timeout → engine stopped
  if (micros() - lastRPMUpdate > RPM_TIMEOUT) {
    rpm = 0;
  }

 // -------- DISPLAY RPM (SLOW REFRESH) --------
if (millis() - lastLCDUpdate >= LCD_REFRESH) {
  lastLCDUpdate = millis();

  if (rpm != lastDisplayedRPM) {
    lcd.setCursor(4, 0);
    lcd.print("     ");
    lcd.setCursor(4, 0);
    lcd.print(rpm);

    lastDisplayedRPM = rpm;
  }
}
2

Welcome to the forum

All that on a 16 by 2 LCD display ?

1 Like
3
  1. Do not use single-characters for variables. Use descriptive words.
  2. Why are you assigning periodMicros to p? Just use periodMicros
  3. Why are you using both millis() and micros()? Just use micros()
4

Thanks for advice - still learning. Using a 162 lcd as thats what I had, but for full project will use 2 320480 TFT displays - 1 for speed, odo, Temp, 2nd for RPM. AFR, fuel gauge & fuel consumption(amt of fuel added entered via keypad). This is for an old project car being built with aftermarket ecu, so AFR needed.