Calculator with phone keypad question [closed]

Question

I am not an electronic person and found this site in a my quest for the perfect calculator. I use both a phone and calculator for calculations and find the back and forth to cause me to make errors due to the keypad reversal. Where would I go to find a simple handheld calculator (+,_,*./,% and =) with a keypad that looks like a phone setup. I can't bring my phone into exams and I make less errors with it since I use the phone keypad on a daily basis. A calculator with a phone keypad layout seems like a practical way to cut down on human error.

In the event my dream calculator is not in existence - is it possible to take an existing calculator and move the keys and reprogram it?

Thanks Tara

Answer 1

You may be able to do this - but you may have to experiment with a few cheap calculators. You'll need to open the case of course and the cheapest calculators may be glued together rather than joined with screws. It may be necessary to cut up a membrane keypad overlay and reassemble it and you may need to do some fine soldering work to cut and reconnect the wiring between keypad and PCB COB/chip/blob. You'll need a fine-tip soldering iron and a voltmeter at minimum.

See Easy Calculator Hack

Answer 2

Another approach is to buy a microprocessor based calculator kit such as this nice Arduino-compatible calculator kit rearrange the buttons and reprogram the chip accordingly.

Assembling this kit and reprogramming an Arduino-compatible calculator is certainly not rocket science and ought to be within the capabilities of someone with elementary soldering and programming skills.

The code is here ready to be hacked.

void decodeKeyPress()
{
  tempINT = 0;                                                        // New Dec 20th

  // KeyPad Layout
  //
  // Columns      Rows
  //   3 2 1 0
  //  
  //   7 8 9 /    0
  //   4 5 6 *    1
  //   1 2 3 -    2
  //   . 0 = +    3

  // Value mapping for decoding
  //     12  8  4  0
  //     13  9  5  1
  //     14  10 6  2
  //     15  11 7  3

  // commandType => 1="+", 2="-", 3="/", 4="*", 5="=", 6="Clear"

  for (i=0; i < 4; i++)                                                // This decodes the Rows
  {
    if(bitRead(rawKeys, i))
      //if(bitRead(rawKeyArray[column], i))   
    {
      tempINT = i;
      break;
    }
  } 

  currentKey = (column*4)+tempINT;

  if(KeyDown[currentKey] == false)
  {

    KeyOK = true;
    KeyDown[currentKey] = true;

    switch (currentKey) 
    {
    case 0:    
      KeyValue =  3;
      commandFlag = true;
      break;

    case 1:    
      KeyValue =  4;
      commandFlag = true;
      break;

    case 2:    
      KeyValue =  2;
      commandFlag = true;
      break;

    case 3:    
      KeyValue =  1;
      commandFlag = true;
      break;

    case 4:    
      KeyValue =  9;
      break;

    case 5:    
      KeyValue =  6;
      break;

    case 6:    
      KeyValue =  3;
      break;

    case 7:    
      KeyValue =  5;
      commandFlag = true;
      break;

    case 8:    
      KeyValue =  8;
      break;

    case 9:    
      KeyValue =  5;
      break; 

    case 10:    
      KeyValue =  2;
      break;

    case 11:    
      KeyValue =  11;
      decimalFlag = true;     
      break;  

    case 12:    
      KeyValue =  7;
      break;

    case 13:    
      KeyValue =  4;
      break; 

    case 14:    
      KeyValue =  1;
      break;

    case 15:    
      KeyValue =  0;
      break;  

      //    case 16:                                              // Clear
      //      KeyValue =  6;
      //      commandFlag = true;
      //      break; 
    default:                                                      // Should never get here
      KeyOK = false;
      KeyValue =  0;
      ErrorFlag = true;
      ErrorCode = 4; 
      //  KeyDown[currentKey] = false;
    }
  }
  else
  {
    KeyOK = false;                                                // Not a new key being pressed
  }
}