Atan oscilloscope and serial plotter

Projects Programming
1

Hi
Why atan on oscilloscope is correct = strait about 30deg line but on serial plotter not = it is vary from 10 to - 140deg ?

Ux _Uy
Ux _Uy1310×848 83.9 KB 

// DC bias 2000
float Ux ;
float Uy ;
float Uxb ;
float Uyb ;
int DEG;

void setup()
{
  Serial.begin(115200);
}

void loop()
{
  Ux = analogRead(PA0);
  Uy = analogRead(PA1);
  Uxb = Ux - 2000;      //bias
  Uyb = Uy - 2000;      //bias

  // DEG = degrees(atan2(Ux, Uy));
  DEG = degrees(atan2(Uxb, Uyb));

  Serial.print(" DEG  =  ");
  Serial.print(DEG);

  Serial.print("    10 = ");
  Serial.print(10);
  Serial.print("   -140 = ");
  Serial.print(-140);

  Serial.println();
  delay(20);
}
2

Try this.

// DC bias 512 (ADC 0..1023)
const float dcBias = 512;

float
Ux,
Uy,
DEG
;

void setup ()
{
  Serial.begin ( 115200 );
}

void loop ()
{
  Ux = analogRead ( A0 ) - dcBias;
  Uy = analogRead ( A1 ) - dcBias;
  
  DEG = degrees ( atan2 ( Uy, Ux ) );
  
  Serial.print ( DEG );
  Serial.print ( ',' );
  Serial.print ( 180 );
  Serial.print ( ',' );
  Serial.println ( -180 );
  delay ( 100 );
}
3

Thanks
The Same

4

Are you sure you're comparing "apples" with "apples" ?

What are the data-points (Ux, Uy) for your comparison and what do they represent (imaginary, real, polar coordinates). Might be missing a conversion or using the wrong data type.

Perhaps your answer is here.

5

can you post your values of Ux and Uy?

6

Ux and Uy are from synchronous detectors taken through capacitors from U2A/U2B
https://radiolocation.tripod.com/NewDQandBeaconFiles/DQsimpleMainSchematic.htm
Pins 1 and 7

sync braian
sync braian726×508 20 KB

7

deg
deg512×738 15.3 KB

8

can you cut them from the serial monitor and post them like code?

1 Like
9

what you posted isn't including the Ux and Uy values used to compute the angle. please add them

10

deg 3
deg 3682×764 34.7 KB

11 
 DEG =  -127.02      UxB  =  -183      UyB=  -138
 DEG =  -131.87      UxB  =  -280      UyB=  -251
 DEG =  -136.53      UxB  =  -310      UyB=  -327
 DEG =  -136.44      UxB  =  -271      UyB=  -285
 DEG =  -114.97      UxB  =  -146      UyB=  -68
 DEG =  -2.67      UxB  =  -9      UyB=  193
 DEG =  14.33      UxB  =  129      UyB=  505
 DEG =  15.67      UxB  =  188      UyB=  670
 DEG =  17.70      UxB  =  201      UyB=  630
 DEG =  12.75      UxB  =  105      UyB=  464
 DEG =  -13.28      UxB  =  -55      UyB=  233
 DEG =  -105.99      UxB  =  -164      UyB=  -47
 DEG =  -135.33      UxB  =  -257      UyB=  -260
 DEG =  -140.09      UxB  =  -312      UyB=  -373
 DEG =  -140.33      UxB  =  -311      UyB=  -375
 DEG =  -135.19      UxB  =  -297      UyB=  -299
 DEG =  -126.91      UxB  =  -233      UyB=  -175
 DEG =  -109.68      UxB  =  -151      UyB=  -54
 DEG =  -49.04      UxB  =  -91      UyB=  79
 DEG =  -22.72      UxB  =  -67      UyB=  160
 DEG =  -11.81      UxB  =  -37      UyB=  177
 DEG =  -27.88      UxB  =  -64      UyB=  121
 DEG =  -95.40      UxB  =  -127      UyB=  -12
 DEG =  -126.75      UxB  =  -221      UyB=  -165
 DEG =  -135.79      UxB  =  -285      UyB=  -293
 DEG =  -135.64      UxB  =  -265      UyB=  -271
 DEG =  -62.94      UxB  =  -92      UyB=  47
 DEG =  21.98      UxB  =  348      UyB=  862
 DEG =  26.23      UxB  =  917      UyB=  1861
 DEG =  28.61      UxB  =  1129      UyB=  2070
 DEG =  26.47      UxB  =  1011      UyB=  2
12

Thanks, looks like the main board schematic from here. Beyond my expertise so I'll sit this out.

13

the values you posted match the values calculated on my laptop for atan2 (x, y)

but arguments to atan2 are typically (y, x)

    (y,x)   ( x,y)      x      y
  -142.98  -127.02   -183   -138
  -138.13  -131.87   -280   -251
  -133.47  -136.53   -310   -327
  -133.56  -136.44   -271   -285
  -155.03  -114.97   -146    -68
    92.67    -2.67     -9    193
    75.67    14.33    129    505
    74.33    15.67    188    670
    72.30    17.70    201    630
    77.25    12.75    105    464
   103.28   -13.28    -55    233
  -164.01  -105.99   -164    -47
  -134.67  -135.33   -257   -260
  -129.91  -140.09   -312   -373
  -129.67  -140.33   -311   -375
  -134.81  -135.19   -297   -299
  -143.09  -126.91   -233   -175
  -160.32  -109.68   -151    -54
   139.04   -49.04    -91     79
   112.72   -22.72    -67    160
   101.81   -11.81    -37    177
   117.88   -27.88    -64    121
  -174.60   -95.40   -127    -12
  -143.25  -126.75   -221   -165
  -134.21  -135.79   -285   -293
  -134.36  -135.64   -265   -271
   152.94   -62.94    -92     47
    68.02    21.98    348    862
    63.77    26.23    917   1861
    61.39    28.61   1129   2070
     0.11    26.47   1011      2
14

That will be another angle of the triangle but will not make angle constant as on oscilloscope (straight line )

15

as i said, the values are correct for args (x,y)

the result of atan2(x,y) is 90 (Pi/2) - atan2(y,x)

16

The problem is not in the numbers, but why does the serial plotter have large variable angle values while the oscilloscope does not

17

bear in mind that the serial plotter is not an x,y plotter. it plots each value on a line as a separate plot.

can you post the output you send to the serial plotter captured on the serial monitor?

18

It is not what is on post #11 ?

19

assuming the serial plotted ignores the "DEG=" it's just going to sequentially plot the numeric values as three separate plots

the serial plotter is not an x-y plotter

20

Thanks I will look for solution.