Devide 12v square wave signal and output 5v squarewave

I am still learning, only had an arduino about 3 weeks, and before that never touched C, I have done some VB, but that was also self taught so I don't want to pick up too many bad habbits early on. So far I've learnt the little I know from the exmaples and from this forum.

I've updated my code with an else function. So now that I've got the frequncy stored into the varilable "sqaure_in" how do I output a frequency?

/*
Read square wave speed signal in on pin2 and output squarewave speed on pin4
 */

volatile uint32_t lastPulseTime = 0;
volatile uint32_t lastPulseWidth = 0;


const int speed_in = 2; //sqaure wave input from speed source 
const int gear_in = 3;     //gear select input 
const int speed_out = 4; //sqaure wave output

// variables for calculation
const float ratio1 = 1/ 2.315;
const float ratio2 = 1/ 1.731;
const float FD = 1 / 4.7;
const float idler = 1.04;
const float pulses = 4; //pulses per simultated revolution
float square_in; //speed received
float square_out; //speed to send

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.

  pinMode(speed_in, INPUT);
  pinMode(speed_out, OUTPUT);
  pinMode(gear_in, INPUT);

attachInterrupt(0, registerPulse, RISING);
}

// the loop routine runs over and over again forever:
void loop() {
  //Sample data to test
  square_in = 1000000UL / lastPulseWidth;


/*
 read the square wave speed input from "speed_in" into variable "sqaure_in"
*/



  if (gear_in == HIGH) {        //ratio1 is selected
    square_out = square_in / 2 * ratio1 / idler * FD * pulses; 
  }//end of ratio1


else{        //ratio2 is selected
  square_out = square_in / 2 * ratio2 / idler * FD * pulses;
  }//end of ratio2


/*
  //output the variable "sqaure_out" as square wave to "Speed_out"
*/
}
void registerPulse() {
  uint32_t cur = micros();
  lastPulseWidth = cur - lastPulseTime;
  lastPulseTime = cur;
}

You're still missing the digitalRead

An optocoupler may be your safest way to translate the voltage. Car voltages are not always clean 12V and can go as high as 18v. A voltage divider wouldn't protect against that. Since you will be driving an LED on the 12V side, just select a proper resistor to keep the current under the transmitter IF spec. Most I have looked at are around 50mA, so around 240 ohms (330 is probably a little safer which is about 36mA.)

Are you just using the arduino to translate the input pulses of 12v to output pulses of 5v or are you using the arduino to actually calculate the RPM? If the latter, I am not sure why you need to output the pulses on another pin.

AWOL:
You're still missing the digitalRead

/*
Read square wave speed signal in on pin2 and output squarewave speed on pin4
 */

volatile uint32_t lastPulseTime = 0;
volatile uint32_t lastPulseWidth = 0;


const int speed_pin = 2; //sqaure wave input from speed source 
const int gear_pin = 3;     //gear select input 
const int speed_out = 4; //sqaure wave output

// variables for calculation
const float ratio1 = 1/ 2.315;
const float ratio2 = 1/ 1.731;
const float FD = 1 / 4.7;
const float idler = 1.04;
const float pulses = 4; //pulses per simultated revolution
float square_in; //speed received
float square_out; //speed to send
int gear; // current gear selected
// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.

  pinMode(speed_pin, INPUT);
  pinMode(speed_out, OUTPUT);
  pinMode(gear_pin, INPUT);

  attachInterrupt(0, registerPulse, RISING);
}

// the loop routine runs over and over again forever:
void loop() {
  //Sample data to test
  square_in = 1000000UL / lastPulseWidth;


  /*
 read the square wave speed input from "speed_in" into variable "sqaure_in"
   */


  gear = digitalRead(gear_pin);
  if (gear == HIGH) {        //ratio1 is selected
    square_out = square_in / 2 * ratio1 / idler * FD * pulses; 
  }//end of ratio1


  else{        //ratio2 is selected
    square_out = square_in / 2 * ratio2 / idler * FD * pulses;
  }//end of ratio2


  /*
  //output the variable "sqaure_out" as square wave to "Speed_out"
   */
}
void registerPulse() {
  uint32_t cur = micros();
  lastPulseWidth = cur - lastPulseTime;
  lastPulseTime = cur;
}

Sorry, I see what you mean now, I've now added a a digtialread for the gear. I don't understand how I can get the frequncy from pin2 into the registerpulse function??

Retroplayer:
An optocoupler may be your safest way to translate the voltage. Car voltages are not always clean 12V and can go as high as 18v. A voltage divider wouldn't protect against that. Since you will be driving an LED on the 12V side, just select a proper resistor to keep the current under the transmitter IF spec. Most I have looked at are around 50mA, so around 240 ohms (330 is probably a little safer which is about 36mA.)

Are you just using the arduino to translate the input pulses of 12v to output pulses of 5v or are you using the arduino to actually calculate the RPM? If the latter, I am not sure why you need to output the pulses on another pin.

the output from th ECU is regulated to 12v, however, I've just googled optocoupler and it looks that it could be a good idea, I assume these a fast enough?

I'm using the arduino to calculate the RPM and then output a different RPM based on another input (gear selector)

Another way would be to clamp the 12 volt pulse to the + 5volt supply with either a fast switching diode(1N4148) or a small signal schottky diode(1N5711) ..It would require a series resistor from the 12v pulse source to the diode clamp,then another voltage divider to drop the approx 5.5 volt pulse to a safer 4.5 volt level.It would mean a few more components but should work.I never did this so if someone thinks of a problem with this please jump in.
jolphil

The following formula moves your floats to integers (better uint32_t, precision: 3 digits behind the point):

square_out = square_in * 201UL / 1138UL ; // case ratio1
square_out = square_in * 420 / 1777; // case ratio2

Output can be:

uint32_t lastEdge = 0;
byte state = 0;

void loop() {
  uint32_t outPulse = 500000UL / square_out; // get pulse length (not wave length)
  uint32_t m = micros();
  if (m - lastEdge >= outPulse) {
    state = ! state;
    digitalWrite(out_pin, state);
    lastEdge = m;
  }
}

I would optimize a bit more and do the whole calculation only if the lastPulseWidth value changed.

Jimster:
I've just googled optocoupler and it looks that it could be a good idea, I assume these a fast enough?

That depends on the one you select. Most I have looked at would be fast enough. Just translate your PPS to BPS in the datasheets.

Pylon, thanks for all your input.

pylon:
The following formula moves your floats to integers (better uint32_t, precision: 3 digits behind the point):

square_out = square_in * 201UL / 1138UL ; // case ratio1

square_out = square_in * 420 / 1777; // case ratio2

Where would I add this code, in the main void loop?
so by adding that code, I could set all my variables to integers? What role does the "UL" have?

Is this the correct implimentation?

/*
Read square wave speed signal in on pin2 and output squarewave speed on pin4
 */

volatile uint32_t lastPulseTime = 0;
volatile uint32_t lastPulseWidth = 0;


const int speed_pin = 2; //sqaure wave input from speed source 
const int gear_pin = 3;     //gear select input 
const int speed_out = 4; //sqaure wave output

// variables for calculation
const int ratio1 = 1/ 2.315;
const int ratio2 = 1/ 1.731;
const int FD = 1 / 4.7;
const int idler = 1.04;
const int pulses = 4; //pulses per simultated revolution
int square_in; //speed received
int square_out; //speed to send
int gear; // current gear selected
// the setup routine runs once when you press reset:
uint32_t lastEdge = 0;
byte state = 0;

void setup() {                
  // initialize the digital pin as an output.

  pinMode(speed_pin, INPUT);
  pinMode(speed_out, OUTPUT);
  pinMode(gear_pin, INPUT);

  attachInterrupt(0, registerPulse, RISING);
}

// the loop routine runs over and over again forever:
void loop() {
  //Sample data to test
  square_in = 1000000UL / lastPulseWidth;


  /*
 read the square wave speed input from "speed_in" into variable "sqaure_in"
   */


  gear = digitalRead(gear_pin);
  if (gear == HIGH) {        //ratio1 is selected
    square_out = square_in / 2 * ratio1 / idler * FD * pulses; 
  }//end of ratio1


  else{        //ratio2 is selected
    square_out = square_in / 2 * ratio2 / idler * FD * pulses;
  }//end of ratio2


  /*
  //output the variable "square_out" as square wave to "Speed_out"
     */
     
     uint32_t outPulse = 500000UL / square_out; // get pulse length (not wave length)
  uint32_t m = micros();
  if (m - lastEdge >= outPulse) {
    state = ! state;
    digitalWrite(speed_out, state);
    lastEdge = m;
  }
     
     
}
void registerPulse() {
  uint32_t cur = micros();
  lastPulseWidth = cur - lastPulseTime;
  lastPulseTime = cur;
}

I have just found out some more info on the sqaurewave speed output from the ECU. The signal is 50% duty so the pulse length is determined by the frequency.The ECU updates the tachometer output every 50mS.

I'm hoping to read the signal in quicker than every 50ms to make sure that I'm not losing data.

I understand that the UNO is 16MHz, but how fast does that mean it could read and ouput data using my code?

Where would I add this code, in the main void loop?

That code has to go into your ratio selector if statement like this:

  if (gear == HIGH) {        //ratio1 is selected
    square_out = square_in * 201UL / 1138UL; 
  }//end of ratio1
  else{        //ratio2 is selected
    square_out = square_in * 420UL / 1777UL;
  }//end of ratio2

so by adding that code, I could set all my variables to integers? What role does the "UL" have?

Yes, you now have to define your variables this way:

uint32_t square_in = 0;
uint32_t square_out = 0;

The UL hints the compiler that it should recognize the given integer constants as "unsigned long", meaning 32bit positive integers.

Ahh right,

So in this line of code
square_out = square_in * 201UL / 1138UL;

where did the numbers 201 abd 1138 come from?

Your calculation

square_out = square_in / 2 * ratio1 / idler * FD * pulses;

is the same as (constants replaced)

square_out = square_in / 2 / 2.315 / 1.04 / 4.7 * 4;

which is the same as (constants pre-calculated)

square_out = square_in * 0.176745271;

and 201 / 1138 = 0.176625659, which is the same factor with a precision of 3 digits after the point.

Very clever, mathimatically, how did you get to those numbers?

It's not just electronics and c I need to learn

how did you get to those numbers?

Take an estimate and approximate till you have the desired precision.

very clever

I've updated the code:

/*
Read square wave speed signal in on pin2 and output squarewave speed on pin4
 */

volatile uint32_t lastPulseTime = 0;
volatile uint32_t lastPulseWidth = 0;
uint32_t square_in = 0; //speed received
uint32_t square_out = 0; //speed to send

const int speed_pin = 2; //sqaure wave input from speed source 
const int gear_pin = 3;     //gear select input 
const int speed_out = 4; //sqaure wave output

// variables for calculation

int gear; // current gear selected
// the setup routine runs once when you press reset:
uint32_t lastEdge = 0;
byte state = 0;

void setup() {                
  // initialize the digital pin as an output.

  pinMode(speed_pin, INPUT);
  pinMode(speed_out, OUTPUT);
  pinMode(gear_pin, INPUT);

  attachInterrupt(0, registerPulse, RISING);
}

// the loop routine runs over and over again forever:
void loop() {
  //Sample data to test
  square_in = 1000000UL / lastPulseWidth;


  /*
 read the square wave speed input from "speed_in" into variable "sqaure_in"
   */


  gear = digitalRead(gear_pin);
  if (gear == HIGH) {        //ratio1 is selected
    square_out = square_in * 201UL / 1138UL; 
  }//end of ratio1


  else{        //ratio2 is selected
    square_out = square_in * 420UL / 1777UL;
  }//end of ratio2


  /*
  //output the variable "square_out" as square wave to "Speed_out"
   */

  uint32_t outPulse = 500000UL / square_out; // get pulse length (not wave length)
  uint32_t m = micros();
  if (m - lastEdge >= outPulse) {
    state = ! state;
    digitalWrite(speed_out, state);
    lastEdge = m;
  }


}
void registerPulse() {
  uint32_t cur = micros();
  lastPulseWidth = cur - lastPulseTime;
  lastPulseTime = cur;
}

Does this look right? is there anything which could be done more affectively?

You can eliminate the change from wave length to frequencies and back:

void loop() {
  uint32_t outPulse;

  gear = digitalRead(gear_pin);
  if (gear == HIGH) {        //ratio1 is selected
    outPulse = lastPulseWidth * 1138UL / 201UL; 
  } else {        //ratio2 is selected
    outPulse = lastPulseWidth * 1777UL / 420UL;
  }

  uint32_t m = micros();
  if (m - lastEdge >= outPulse) {
    state = ! state;
    digitalWrite(speed_out, state);
    lastEdge = m;
  }
}

The next step is to do the calculation only if one of the input values have changed:

uint32_t savedPulseWidth = 0;
byte savedGear = LOW;
void loop() {
  uint32_t outPulse;

  gear = digitalRead(gear_pin);
  if (gear != savedGear || lastPulseWidth != savedPulseWidth) {
    savedGear = gear;
    savedPulseWidth = lastPulseWidth;
    if (gear == HIGH) {        //ratio1 is selected
      outPulse = lastPulseWidth * 1138UL / 201UL; 
    } else {        //ratio2 is selected
      outPulse = lastPulseWidth * 1777UL / 420UL;
    }
  }

  uint32_t m = micros();
  if (m - lastEdge >= outPulse) {
    state = ! state;
    digitalWrite(speed_out, state);
    lastEdge = m;
  }
}

Thanks for that, I plan to have my test rig compleated this week to test this on, thanks again for your massive help :smiley: XD