Hi there, I have a problem in my code - I am presuming - that will not allow my auto-start function to work correctly. The "starter motor" relay will activate if the value condition is met, but will not deactivate when this is not true. I checked the serial values and they are reading correctly. I had this working correctly some time ago, then the file was lost, and now after recreating it, the "engine start" function will not work correctly. I would be extremely grateful if anyone could suggest a correction I could do to fix this issue. I hope I have formatted this code properly :slight_smile: #include #include LiquidCrystal_I2C lcd(0x27, 20,4); #include #include #define Password_a_Length 8 #define Password_b_Length 8 int ecuRelay = 4; int ignitionRelay=7; int fuelPumpRelay=8; int starterRelay=12; int startButton=5; int buzzerPin=3; int analogPin=A0; float val; char Data_a[Password_a_Length]; char Master_a[Password_a_Length] = "111111#"; byte data_a_count = 0, master_a_count = 0; char Data_b[Password_b_Length]; char Master_b[Password_b_Length] = "222222#"; byte data_b_count = 0, master_b_count = 0;bool Pass_is_good;char customKey; const byte ROWS = 4; const byte COLS = 3; char hexaKeys[ROWS][COLS] = { {'1', '2', '3'}, {'4', '5', '6'}, {'7', '8', '9'}, {'*', '0', '#'} }; byte rowPins[ROWS] = {31, 33, 35, 37}; byte colPins[COLS] = {39, 41, 43}; Keypad customKeypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS); void setup(){ Serial.begin(9600); lcd.init(); lcd.backlight(); pinMode(ecuRelay, OUTPUT); pinMode(ignitionRelay, OUTPUT); pinMode(fuelPumpRelay, OUTPUT); pinMode(starterRelay, OUTPUT); pinMode(startButton, INPUT); digitalWrite(startButton,HIGH); pinMode(analogRead, INPUT); digitalWrite(starterRelay, LOW); } void loop(){ val=analogRead(analogPin); val=(5./1023.)*val; Serial.println(val); lcd.setCursor(4,1); lcd.print("NISSAN 200SX"); customKey = customKeypad.getKey(); if (customKey){ Data_a[data_a_count] = customKey; data_a_count++; Data_b[data_b_count] = customKey; data_b_count++; } if(data_a_count == Password_a_Length-1){ if(!strcmp(Data_a, Master_a)){ lcd.clear(); lcd.setCursor(3,0); delay(250); lcd.print("Hello, Driver 1"); delay(50); tone(buzzerPin, 2100, 300); delay(100); tone(buzzerPin, 3225, 120); delay(50); tone(buzzerPin, 4300, 80); delay(1000); lcd.setCursor(3,2); lcd.print("Press To Start"); digitalWrite(ecuRelay, HIGH); delay(500); digitalWrite(ignitionRelay, HIGH); delay(500); digitalWrite(fuelPumpRelay, HIGH); delay(3000); digitalWrite(fuelPumpRelay, LOW); delay(500); lcd.clear(); } if(data_b_count == Password_b_Length-1){ if(!strcmp(Data_b, Master_b)){ lcd.clear(); lcd.setCursor(3,0); delay(250); lcd.print("Welcome, Driver 2"); delay(50); tone(buzzerPin, 2100, 80); delay(85); tone(buzzerPin, 2662.5, 50); delay(90); tone(buzzerPin, 3225, 50); delay(100); tone(buzzerPin, 4300, 50); delay(100); lcd.setCursor(3,2); lcd.print("Press To Start"); digitalWrite(ecuRelay, HIGH); delay(1000); digitalWrite(ignitionRelay, HIGH); delay(1000); digitalWrite(fuelPumpRelay, HIGH); delay(3000); digitalWrite(fuelPumpRelay, LOW); delay(500); lcd.clear(); } if (digitalRead(startButton)== LOW) { delay(250); lcd.clear(); lcd.setCursor(6,1); lcd.print("Starting"); lcd.setCursor(7,2); lcd.print("Engine!"); tone(buzzerPin, 4300, 75); delay(80); tone(buzzerPin, 4300, 100); delay(150); digitalWrite(fuelPumpRelay, HIGH); delay(1500); if (val<=2.5) { digitalWrite(starterRelay, HIGH); } else{ digitalWrite(starterRelay, LOW); delay(3000); } } delay(3000); lcd.clear(); } else{ delay(100); } clearData(); } } void clearData(){ while(data_a_count or data_b_count!=0){ Data_a[data_a_count--] = 0; Data_b[data_b_count--] = 0; } return; }

Well after a few hours of head scratching, I finally understood how to use millis in the most basic form, and apply it to my program. :slight_smile: I am pleased to say that it works, although not as nice and well timed as it was previously, and no beeps on password acceptance as they are continuous in the loop. So here is the code I currently am using - Feel free to point out any improvements I could make! :smiley: #include #include LiquidCrystal_I2C lcd(0x27, 20, 4); #include #include #define Password_a_Length 8 #define timeCount millis int neutralSwitch = 11; int ecuRelay = 4; int ignitionRelay = 7; int fuelPumpRelay = 8; int starterRelay = 12; int startButton = 5; int buzzerPin = 3; int rpmVoltage = A0; float val2; unsigned long val = 0; char Data_a[Password_a_Length]; char Master_a[Password_a_Length] = "111111#"; byte data_a_count = 0, master_a_count = 0; bool Pass_is_good; char customKey; const byte ROWS = 4; const byte COLS = 3; char hexaKeys[ROWS][COLS] = { {'1', '2', '3'}, {'4', '5', '6'}, {'7', '8', '9'}, {'*', '0', '#'} }; byte rowPins[ROWS] = {31, 33, 35, 37}; byte colPins[COLS] = {39, 41, 43}; Keypad customKeypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS); void setup() { Serial.begin(9600); lcd.init(); lcd.backlight(); pinMode(neutralSwitch, INPUT); digitalWrite(neutralSwitch, LOW); pinMode(ecuRelay, OUTPUT); pinMode(ignitionRelay, OUTPUT); pinMode(fuelPumpRelay, OUTPUT); pinMode(starterRelay, OUTPUT); pinMode(startButton, INPUT); digitalWrite(startButton, HIGH); pinMode(rpmVoltage, INPUT); } void loop() { val = timeCount(); val2 = analogRead(rpmVoltage); val2 = (5. / 1023) * val2; Serial.println(val2); lcd.setCursor(4, 1); lcd.print("NISSAN 200SX"); customKey = customKeypad.getKey(); if (customKey) { Data_a[data_a_count] = customKey; data_a_count++; } if (data_a_count == Password_a_Length - 1) { if (!strcmp(Data_a, Master_a)) { if (digitalRead(neutralSwitch) == HIGH) { tone(buzzerPin, 1500, 500); } else { if (val > 9000) { digitalWrite(fuelPumpRelay, HIGH); } if (val > 10000) { digitalWrite(ecuRelay, HIGH); } if (val > 12000) { digitalWrite(ignitionRelay, HIGH); } if (val > 13000) { lcd.setCursor(3, 2); lcd.print("Ready To Start"); } if (val > 14000) { if (digitalRead(startButton) == LOW) { digitalWrite(starterRelay, HIGH); } } if (val2 >= 0.5) { digitalWrite(starterRelay, LOW); lcd.clear(); clearData(); lcd.noBacklight(); } } } } } void clearData() { while (data_a_count != 0) { Data_a[data_a_count--] = 0; } return; }

Yes I would be happy to, thankyou. :slight_smile: Driver enters one of 2 available 6-digit codes followed by the hash key. Ignition relay, ECU relay and Fuel pump relay activate - the Fuel pump relay remains on only for 5 seconds, the others remain on indefinitely. Display prompts driver to press start button, so button must be depressed within a few seconds or the unit will need reset to try again. With successful start button input, the display reads "starting engine", and the fuel pump relay will activate again, and remain on until power off. The starter relay will now activate, and remain energised until the value from the potentiometer reads more than 2.5. This represents a voltage supplied by the vehicles ECU. At this moment, the Starter relay should deactivate.

This would be the end of the program, and the unit should remain in this final state until power off. Thanks again for the help everyone. :slight_smile:

[image] nizeianson: remain in this final state until power off. Okay... You probably will want status "dials" on the LCD for each of the relays, pumps, engine, voltage... something like that?

Actually, this was a happy mistake that it reverts back to saying Nissan, as there is no further input needed it seems good this way! :smiley:

I had not thought about a status of the relays being something I could put on the LCD, as I am still learning the basics, but this is something useful that the screen could be used for.

Okay. I'll see what I can tinker with. About the "long start"... My uncle had a car that needed a "enable spark" switch turned on before pressing an "ignition" button. You could press "ignition" and the starter motor would do its motor thing, but only when "spark enable" was on, would the car start. I've also driven multi-purpose vehicles that needed 17-switches set to start. Nothing is too long.

I never like projects that could have strange undesirable actions and unpredictable failure modes . ( fail safety , processor crash ?) You need to check it’s not in gear the brakes are on , it’s not in a closed space such as a garage, there is no one inside it (child?) etc etc . What happens in an accident ? Will it start ? What’s to stop it switching the engine off ? When it drives off by itself the insurance is unlikely to pay out , it may also be illegal to have a car running with no body in it , you need to check that . I would just get in turn the key and drive off .

The worst case scenario is I would use it but without the auto-start function, this way I can create a 'limp mode' scenario instead with the extra relay, which is perfect when leaving the car at a garage for example, they won't have full power available. But I will include a neutral switch input into the program to protect against starting in gear, as I have this switch on the car available. But other than the auto-start, it would operate exactly as any other immobiliser does.

I was an Auto Electrician by trade for many years, so am familiar with these systems and how they all work. Just to add, in case anyone thought I'm in over my head or anything. :slight_smile:

Thankyou so much, I greatly appreciate your help and any improvements that could be made to the project. I did also mean to say I am using the Arduino 4 relay piggyback board, just in case that helps you. Thankyou again

Vehicle Immobiliser with Auto-Start function - A small problem!

Projects Programming

xfpd October 23, 2026, 1:21pm 28

This is due to delay() allowing nothing to happen while it counts milliseconds.

Yes, this will stop the unresponsiveness, but it will need a "finite state machine" which will step from state to state as actions (pswd, button) or time occur.

Topic		Replies	Views
Project works for a while, then hangs General Guidance	43	799	August 1, 2026
Gestione stepper NEMA17 con A4988: uso della libreria Bounce Software	56	706	February 12, 2026
Hello, I'm a new to Arduino and this forum General Guidance	39	418	November 11, 2025
Using Millis to Turn On/Off Relay for a set interval Programming	21	3743	October 19, 2021
Control cabinet with 12 electric locks Programming	24	479	April 10, 2025

Vehicle Immobiliser with Auto-Start function - A small problem!

Related topics