Better voltage distance by swapping the 4k7 and 1k values.

[Koepel]

Hi, I have made a quick and dirty test sketch to find the best voltage distance between the keys. It turns out that if the high-side resistors at the rows are 1k and the low-side resistors at the columns are 4k7, then I get better results. My test-sketch is based on your ShowRange.ino sketch.

A few results of the minimum voltage distance between keys with certain resistors:

4k7 and 1k 	: 0.01615
1k and 4k7 	: 0.05183
1k and 3k9 	: 0.05957
2k7 and 10k 	: 0.06182
4k7 and 18k 	: 0.06035

Have you already optimized the results with 1k and 4k7 values ? Did you swap them or does my sketch swap them ?

float voltages[16];

void setup() 
{
  Serial.begin(115200);
  Serial.println( "---START------------------");

  Serial.println( "Finding the best resistors values,");
  Serial.println( "for the maximum voltage distance between keys.");

  Serial.println( "A few fixed values:");
  float x;

  Serial.print( "  4k7 and 1k \t: ");
  fillValues( 4, 4, 4700, 1000, 5);
  x = findMin();
  Serial.println( x, 5);

  Serial.print( "  1k and 4k7 \t: ");
  fillValues( 4, 4, 1000, 4700, 5);
  x = findMin();
  Serial.println( x, 5);

  Serial.print( "  1k and 3k9 \t: ");
  fillValues( 4, 4, 1000, 3900, 5);
  x = findMin();
  Serial.println( x, 5);

  Serial.print( "  2k7 and 10k \t: ");
  fillValues( 4, 4, 2700, 10000, 5);
  x = findMin();
  Serial.println( x, 5);

  Serial.print( "  4k7 and 18k \t: ");
  fillValues( 4, 4, 4700, 18000, 5);
  x = findMin();
  Serial.println( x, 5);

  Serial.println( "Calculate resistors...");

  float maxDistance = 0.0;
  
  for( long r1 = 100; r1<22000; r1+=100)
  {
    for( long r2 = 100; r2<22000; r2+=100)
    {
      fillValues( 4, 4, r1, r2, 5);

      float minimal = findMin();

      // Don't print values that are too close to zero.
      // Also print values that are close to the best value.
      if( minimal > (maxDistance - 0.0001) && minimal > 0.001)
      {
        maxDistance = minimal;

        Serial.print( "  ");
        Serial.print( r1);
        Serial.print( ",\t");
        Serial.print( r2);
        Serial.print( "\t : ");
        Serial.print( maxDistance, 5);
        Serial.println();
      }
    }
  }
  Serial.println( "---THE-END----------------");
}

void loop() 
{
}

void fillValues(int rows, int cols, long Rrows, long Rcols, int Volt)
{
   for( int R = 0; R < rows; R++)
   {
     for( int C = 0; C<cols; C++)
     {
        float V = (5.0f * float( Rcols )) / (float(Rcols) + (float(Rrows) * R) + (float(Rcols) * C));
        voltages[(R*4) + C] = V;
//        Serial.print(V, 3); Serial.print(F("\t"));
     } 
//     Serial.println();  
   }
}

float findMin()
{
  float absdist[16];

  // find minimal distance for each one, in positive distance
  for( int i=0; i<16; i++)
  {
    float min = 100.0;
    for( int j=0; j<16; j++)
    {
      if( i != j)   // don't compare to own voltage
      {
        float distance = voltages[j] - voltages[i];
        if( distance < 0.0)
          distance = -distance;

        if( distance < min)
          min = distance;
      }
    }
    absdist[i] = min;
  }

//  printValues( absdist);

  // find overal minimal distance 
  float overallmin = 100.0;
  for( int i=0; i<16; i++)
  {
    if( absdist[i] < overallmin)
      overallmin = absdist[i];
  }

  return( overallmin);
}

void printValues( float data[])
{
  for( int i=0; i<4; i++)
  {
    for( int j=0; j<4; j++)
    {
      Serial.print(data[(i*4)+j], 3); 
      Serial.print(F("\t"));
    }
    Serial.println();
  }
}