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;
}
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.
/*
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
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?