[ADXL 345] saving and reusing old variable value, while it's being actualised.

Projects Programming
1

Firstly, I want to say hello, as I'm newbie on this forum.

I'm working on my first arduino project which is self-balancing one axis swing.

Here is what I want from code :

In first void loop run, I have 'new_angle' variable which is first mesurement of current angle.
Then, this angle is being saved in other variable named 'old_angle'.

In following void loop runs I want to have 'new_angle, being actualised, while old_angle would have the value of new_angle from previous runs. So that I can calculate angle difference in time (acceleration).

The problem is, that old_angle is being actualised together with new_angle, so I can't calculate the difference.

I've tried many ways to solve this, but none of them were good enough. The best I did, was adding a counter variable, and actualising old_angle when counter was even and new_angle when counter was odd.

Here's my code:

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_ADXL345.h>
#include <math.h>

/* Assign a unique ID to this sensor at the same time */
Adafruit_ADXL345 accel = Adafruit_ADXL345(12345);


int outPin = 5;
int outPin2 = 6;
int outPin4 = 10;
int outPin3 = 11;

void setup(void) 
{
  Serial.begin(9600);
  Serial.println("Accelerometer Test"); Serial.println("");
  
  /* Initialise the sensor */
  if(!accel.begin())
  {
    /* There was a problem detecting the ADXL345 ... check your connections */
    Serial.println("Ooops, no ADXL345 detected ... Check your wiring!");
    while(1);
  }

  /* Set the range to whatever is appropriate for your project */
  accel.setRange(ADXL345_RANGE_2_G);
  accel.setDataRate(ADXL345_DATARATE_1600_HZ);


pinMode(outPin, OUTPUT);
pinMode(outPin2, OUTPUT);
pinMode(outPin3, OUTPUT);
pinMode(outPin4, OUTPUT);
}

void loop(void) 
{
 
  sensors_event_t event; 
  accel.getEvent(&event);
  
  float y = event.acceleration.y;
  float z = event.acceleration.z;
  float alfa_old;
   
   // correction for each axis used  
  if(y>0)
  y=event.acceleration.y-0.86;
  if(y<0)
  y=event.acceleration.y-0;
  if(z>0)
  z=event.acceleration.z+0.16;
  if(z<0)
  z=event.acceleration.z+1.02;
 
 // calculating angles and acceleration
  float alfa_new = atan2(y , z) * 180/PI;
  float Dalfa=abs(alfa_new-alfa_old);
  alfa_old = alfa_new;
    
    
  
  
  
   /* Display the results (acceleration is measured in m/s^2) */
  Serial.print("alfa_old: "); Serial.print(alfa_old); Serial.print("  ");
  Serial.print("Dalfa: "); Serial.print(Dalfa); Serial.print("  ");
  Serial.print("alfa_new: "); Serial.print(alfa_new); Serial.print("  ");
  Serial.print("Y: "); Serial.print(y); Serial.print("  ");
  Serial.print("Z: "); Serial.print(z); Serial.print("  ");Serial.println("m/s^2 ");

  
  // demo work for engines
 // if(y>=0){
   // analogWrite(outPin, y+50);
  //  digitalWrite(outPin2, LOW);  //prawy
  //  analogWrite(outPin3, 0);
  //  digitalWrite(outPin4, LOW);
 // }
 // if(y<=0){
    
   // analogWrite(outPin, 0 );
   // digitalWrite(outPin2, LOW);   //lewy
    //analogWrite(outPin3, abs(y)+50);
   // digitalWrite(outPin4, LOW);
  //}
  
  
  delay(15);
   
}

Greetings and thanks for any help.

2

Make alfa_old static or global?

3

Here is what I want from code :

In first void loop run, I have 'new_angle' variable which is first mesurement of current angle.
Then, this angle is being saved in other variable named 'old_angle'.

You do not have any variables named new_angle or old_angle. If you are going to talk about your code, it's best to use names that are ACTUALLY defined in your code.

  float alfa_old;

I'm guess that this uninitialized local variable should be initialized AND should be static.

4

PaulS:
If you are going to talk about your code, it's best to use names that are ACTUALLY defined in your code.

sorry for that.

AWOL:
Make alfa_old static or global?

PaulS:
I'm guess that this uninitialized local variable should be initialized AND should be static.

I've initialized it, and it's now global.
Here's what I've hanged:

static float alfa_old = 0;
             void setup (void){
...
} 
void loop(void) 
{ ...

float alfa_new = atan2(y , z) * 180/PI;
  
  alfa_old = alfa_new;
    
  float Dalfa=abs(alfa_old-alfa_new); 

...
}

Still, the readings are:

5 
alfa_old = alfa_new;
    
  float Dalfa=abs(alfa_old-alfa_new);

Let's figure out what value that difference will have.

6

it will be 0.
After changing to this:

 float alfa_new = atan2(y , z) * 180/PI;
  float Dalfa=abs(alfa_old-alfa_new); 
  alfa_old = alfa_new;

I'm getting unpredictable Dalfa values, when alfa_old and _new are still the same.