Published October 15, 2020 © GPL3+

Automotive Engine Rev-Limiter

Easy implementation of Rev-limiter for Automotive or Motorcycle Engine.

IntermediateFull instructions provided6,720

Things used in this project

Hardware components

Arduino Nano R3

IRF520 Mosfet Driver, Arduino Compatible

5V Relay

LM2569 Voltage Regulator

Inductive Proximity Sensor, Stainless Steel

Machine Screw, M4

Resistor 10k ohm

Mounting Bracket, Bracket

Hand tools and fabrication machines

Soldering iron (generic)

Solder Wire, Lead Free

Hot glue gun (generic)

Drill / Driver, Cordless

Multitool, Screwdriver

Story

Introduction

This project is about automotive engines and how with a bit of elbow grease and a lot of passion you can use an arduino to protect its vital components. An old engine usually does not have a built-in rev-limiter and if you drive it hard enough bad things can happen! Especially an old project car with sentimental value needs to be protected!

The implementation of the electronically controlled and programmable rev-limiter is pretty simple, cheapest than anything aftermarket you can possibly find and lastly it is a very robust design.

The project uses an inductive sensor that measures the rotational speed of the engine. The data from the sensor are fed to the Arduino Nano and if the rotational speed threshold is exceeded the pin that controls the Mosfet becomes 'HIGH' which turns off the relay thus stopping the engine. When the RPMs drop back below the preset threshold the relay is turned on and the cycle repeats.

Electronics Box

It is recommended that the electronics are enclosed in an aluminum box for protection. All the electrical connections can be obtained from the included schematic. The electrical components are widely spaced in order to make troubleshooting easier. The arduino nano is fitted on a breadboard that enables a quick removal for programming or replacing it. The operating voltage of the system (voltage regulator output) should be between 6-12V! In the following pictures you can see the layout of the electronics.

1 / 4 • Electronics Unit

An important detail for the wiring is that the relay should be connected on its Normally Closed pins. This will ensure that the engine will be able to function properly even if the arduino is turned of or malfunctions!

RPM Sensor

The tricky part of the project is the placement of the two bolts that act as triggers to the inductive proximity sensor. They must be placed in a rotating pulley (preferably the crankshaft pulley) and 180 degrees apart. The installation should look like below.

1 / 4 • RPM Sensor Mounting

The distance between the sensor and the bolts should be less than 3mm so that the sensor will change its state. The mounting bracket can be made from anything you want as long as it is strong and placed in the correct position!!

End Result

After the installation of the electronics and after you have uploaded the code to the arduino you have to set desired RPM threshold!! Then you can enjoy the rev-limiter!! I took the liberty to remove a portion of the exhaust and created some awesome FLAMES!!

Code

Arduino Code for Rev-Limiter

// Rev-Limiter Code for Arduino Project Hub
//
//Written by Adrianos Botis: adrianosbotis@gmail.com
//
//Use at your own and change the parameters: rpm_val to set the rpm limit of your engine.
//You can also change the delay of milliseconds at the end of the code to set how fast your engine will be switched on-off.
//


int sensor_pin = 3;
// set number of hall trips for RPM reading (higher improves accuracy)
float sensor_thresh = 5.0;
int ignition = 2;

void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  // make the sensor pin an input:
  pinMode(sensor_pin, INPUT);
  pinMode(ignition, OUTPUT);
}

// this loop routine runs over and over again forever:
void loop() {
  // preallocate values for tach
  float hall_count = 1.0;
  float start = micros();
  bool on_state = false;
  // counting number of times the hall sensor is tripped
  // but without double counting during the same trip
  while(true){
    if (digitalRead(sensor_pin) == 1){
      if (on_state==false){
        on_state = true;
        hall_count+=1.0;
      }
    } else{
      on_state = false;
    }
    
    if (hall_count>=sensor_thresh){
      break;
    }
  }
  
  // print information about Time and RPM
  float end_time = micros();
  float time_passed = ((end_time-start)/1000000.0);
  Serial.print("Time Passed: ");
  Serial.print(time_passed);
  Serial.println("s");
  float rpm_val = (sensor_thresh/(2*time_passed))*60.0;
   if(rpm_val > 8000.0){
     digitalWrite(ignition, HIGH);
     } 
     else { 
     digitalWrite(ignition, LOW);
  } 
  
  Serial.print(rpm_val);
  delay(1);        // delay in between reads for stability
}

Credits

adrianos_botis

3 projects • 7 followers

Automotive Engine Rev-Limiter

Things used in this project

Hardware components

Hand tools and fabrication machines

Story

Introduction

Electronics Box

RPM Sensor

End Result

Schematics

Circuit Schematic

Code

Arduino Code for Rev-Limiter

Github/Arduino Code for Rev-Limiter

Credits

adrianos_botis

Comments

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Automotive Engine Rev-Limiter

Automotive Engine Rev-Limiter

Things used in this project

Hardware components

Hand tools and fabrication machines

Story

Introduction

Electronics Box

RPM Sensor

End Result

Schematics

Circuit Schematic

Code

Arduino Code for Rev-Limiter

Github/Arduino Code for Rev-Limiter

Credits

adrianos_botis

Comments

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