Hi, i have been trting to put together a basic tachometer using an A3144 Hall effect sensor, an arduino NANO and a 7 segment/8DIGIT MAX7219 display, im pretty poor when it comes to actual coding so ive been using information gleaned from the following gihub page....
And the code...
// Frequency timer
// Author: Nick Gammon
// Date: 10th February 2012
// http://www.mikrocontroller.net/attachment/189505/Drehzahlmesser.ino
// some changes by Nicu FLORICA (niq_ro) - see movie from https://youtu.be/9jCCoyg4wmA
// source for LEDControl: http://embedded-lab.com/blog/?p=6862
#include "LedControl.h" // https://github.com/wayoda/LedControl
/*
Now we need a LedControl to work with.
***** These pin numbers will probably not work with your hardware *****
pin 12 is connected to the DataIn
pin 11 is connected to the CLK
pin 10 is connected to LOAD
We have only a single MAX72XX.
*/
LedControl lc=LedControl(12,11,10,1);
int vtot, vs, vsz, vz, vzu, vu, vv;
// Input: Pin D2
volatile boolean first;
volatile boolean triggered;
volatile unsigned long overflowCount;
volatile unsigned long startTime;
volatile unsigned long finishTime;
// here on rising edge
void isr ()
{
unsigned int counter = TCNT1; // quickly save it
// wait until we noticed last one
if (triggered)
return;
if (first)
{
startTime = (overflowCount << 16) + counter;
first = false;
return;
}
finishTime = (overflowCount << 16) + counter;
triggered = true;
detachInterrupt(0);
} // end of isr
// timer overflows (every 65536 counts)
ISR (TIMER1_OVF_vect)
{
overflowCount++;
} // end of TIMER1_OVF_vect
void prepareForInterrupts ()
{
// get ready for next time
EIFR = bit (INTF0); // clear flag for interrupt 0
first = true;
triggered = false; // re-arm for next time
attachInterrupt(0, isr, RISING);
} // end of prepareForInterrupts
void setup ()
{
Serial.begin(115200);
Serial.println("Frequency Counter");
// reset Timer 1
TCCR1A = 0;
TCCR1B = 0;
// Timer 1 - interrupt on overflow
TIMSK1 = bit (TOIE1); // enable Timer1 Interrupt
// zero it
TCNT1 = 0;
overflowCount = 0;
// start Timer 1
TCCR1B = bit (CS20); // no prescaling
// set up for interrupts
prepareForInterrupts ();
// Initialize MAX7219 device
lc.shutdown(0,false); // Enable display
lc.setIntensity(0,8); // Set brightness level (0 is min, 15 is max)
lc.clearDisplay(0); // Clear display register
lc.setChar(0,7,' ',false);// ma asigur ca nu e nimic pe coloana 7 (cea din stanga)
lc.setRow(0,6,B1100010); // afisez litera "n" pe coloane 6
lc.setRow(0,5,B0100000); // afisez litera "i" pe coloane 5
lc.setRow(0,4,B1110011); // afisez litera "q" pe coloane 4
lc.setRow(0,3,B0000001); // afisez semnul "-" pe coloane 3
lc.setRow(0,2,B1000010); // afisez litera "r" pe coloane 2
lc.setRow(0,1,B1100011); // afisez litera "o" pe coloane 1
lc.setChar(0,0,' ',false);// ma asigur ca nu e nimic pe colanea 0 (din dreapta)
delay(2000);
lc.clearDisplay(0); // Clear display register
} // end of setup
void loop ()
{
if (!triggered)
return;
unsigned long elapsedTime = finishTime - startTime;
// float rpm = 60 * F_CPU / float (elapsedTime); // each tick is 62.5 nS at 16 MHz
float rpm = 30 * F_CPU / float (elapsedTime); // each tick is 62.5 nS at 16 MHz
Serial.print ("RPM: ");
Serial.println (rpm);
vtot = rpm;
// calculate number for each figure number
vs = vtot /1000;
vsz = vtot - 1000*vs;
vz = vsz /100;
vzu = vsz - 100*vz;
vu = vzu /10;
vv = vzu - 10*vu;
//vtot = 0;
lc.setChar(0,7,' ',false);
//lc.setRow(0,7,B00111110); // afisez litera "U" pe coloana 7
lc.setChar(0,6,' ',false);
lc.setChar(0,5,' ',false);
//lc.setRow(0,5,B00001001); // afisez "=" pe coloana 5
lc.setChar(0,4,' ',false);
if (vs == 0) lc.setChar(0,3,' ',false); else
lc.setDigit(0,3,vs, false); // afisez miile pe coloana 3
lc.setDigit(0,2,vz, false); // afisez sutele pe coloana 2
lc.setDigit(0,1,vu, false); // afisez zecile pe coloana 1
lc.setDigit(0,0,vv,false);
// }
//Serial.print ("Took: "); // Ausgabe der gezählten counts
//Serial.print (elapsedTime);
//Serial.print (" counts. ");
// so we can read it
delay (500);
prepareForInterrupts ();
} // end of loop
I have the DIN, LOAD/CS and CLK connected to D12, D10 and D11 respectivley, and the DATA pin from the A3144 to D2 on the NANO as mentioned in a comment in the code.
Now, when ive tried the 3144 alone with a LED/resistor to confirm its functioning its fine, its high until magnets close, when close it goes low its all good.
but when i wire it up with the arduino/MAX7219 something isnt correct. a magnet near the 3144 makes no diference whatsoever, when the code is first uploaded it boots up and displays 'niq_ro' - but after that the display is either blank, with no reaction to the presence of a magnet, or it throws up seemingly random numbers, reset the NANO and it just does the same 
the code compiles and uploads fine in the IDE
Now like i said im a beginner when it comes to coding, i usually come back to the arduino when i have a use for it, learn enough to get me through a basic project like this then forget it all by the time the next project comes around, but i would really like to learn more and become slightly more proficient in C++, i started trying to look at the code logically, and allthough it mentions the DATA from the 3144 in a comment, surely that is ignored due to the //? other than that it doesnt explicitly define D2 as the DATA line from 3144 ? im 99% sure im being a fool here and am about to feel foolish, but if it helps me to learn then im willing to accept it lol.
Can someone please help with where im going wrong and point me in the right direction.
any info or advice would be greatly appreciated, and apologies for rambling 
cheers,
josh
