Hi guys, I am very new to this and am doing alot of searching but wanted to see if anyone wanted to give me a boost on the learning curve/project.
I've got a truck that I need to give vehicle speed to the pcm with the standard being 8000 pulses per mile. I have a tone wheel on the drive shaft with 18 teeth that will give me 39312 pulses per mile that I need to convert to 8000 pulses per mile digital to go to the pcm and speedometer. The signal from the sensor is a sine wave which I'll attach a picture of.
The speedometer is a project for another day but it's not drivable until I have the speed for shift points.
I am sure I have left out alot of information but if any one has any pointers it'd be awesome.
That sounds like a job for the map() function. It is a bit confusing to beginners, so if you don't understand it, let us know, and we will explain it in more detail.
DrDiettrich:
More information about the electric circuitry around the tone wheel would be helpful. A wheel doesn't provide electric pulses by itself.
I would but about all the info I have on the sensor is it's a two wire magnetic. It's an automotive sensor so I don't have a data sheet on it. On it's factory wiring diagram you have one pin that is signal return and the other is vehicle speed to pcm. Resistance is listed as 781ohms - 1979ohms.
It is probably a magneto. As the shaft turns with a magnet(s) on it, a coil of wire picks up emf, and sends it out by the two wires. Probably no semiconductors in that circuit.
I also haven't commited to this sensor. I have another sensor, also automotive, that is a 5 volt reference sensor that will give me a square wave if need be.
I think the 5Volt square wave would be easier for the arduino to see, but would that mean you had to provide power (more wires)?
It's good to have a backup option, in case one does not work as expected.
Ok, so I've got the input side of it taken care of. I'm using the 3 wire hall effect and the internal pullup to get a 5v square wave. Now I'm starting to play with the output side of it.
so now i have the input and output working properly but i need to up the output from a 5v pattern to 12v. The output is going to a vehicles pcm so no real load. I've started to look into photocouplers and mosfets, is this the right direction?
i doubt it's done right as this is my first sketch and alot is from other sources but here it is
// Frequency counter sketch, for measuring frequencies low enough to execute an interrupt for each cycle
// Connect the frequency source to the INT0 pin (digital pin 2 on an Arduino Uno)
// Using pin 2 as a pullup, cmp sensor in goes here
volatile unsigned long firstPulseTime;
volatile unsigned long lastPulseTime;
volatile unsigned long numPulses;
void isr()
{
unsigned long now = micros();
if (numPulses == 1)
{
firstPulseTime = now;
}
else
{
lastPulseTime = now;
}
++numPulses;
}
void setup()
{
Serial.begin(9600); // this is here so that we can print the result
digitalWrite(2,HIGH);
pinMode(3,OUTPUT);
}
// Measure the frequency over the specified sample time in milliseconds, returning the frequency in Hz
float readFrequency(unsigned int sampleTime)
{
numPulses = 0; // prime the system to start a new reading
attachInterrupt(0, isr, FALLING); // enable the interrupt
delay(sampleTime);
detachInterrupt(0);
return (numPulses < 3) ? 0 : (1000000.0 * (float)(numPulses - 2))/(float)(lastPulseTime - firstPulseTime);
}
void loop()
{
float freq = readFrequency(50);
int val = freq;
val = map(val, 0, 2184, 0, 2184);
tone(3,val);
Serial.print(val);
Serial.print(freq);
delay(500);
}
I got a mosfet board (tinkerkit t010020) and am now getting a 12v pattern but its very dirty (see attatched pic) from what I've gathered I need a pulldown circuit but I am not sure. In the picture the green is from the arduino and the yellow is the output of the mosfet.
