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• The Android App

  Nitesh Kadyan • 04/03/2018 at 05:16 • 0 comments

  ANDROID APP:

  I modified the demo BLE app by google (here) to work with the HM-11 BLE modules for transferring text messages to the device. The entire source code for the app can be found in the project github repo here.

  A demo video of uploading a text message:
  

• Building the Firmware

  Nitesh Kadyan • 04/03/2018 at 05:09 • 0 comments

  
  

  FIRMWARE:

  Each character to be displayed is stored as 8 bytes in the program memory of ATMEGA. For example char 'A' is stored in 8 bytes as:

  0b00001110, 
  0b00010001,
  0b00010001, 
  0b00010001,
  0b00011111, 
  0b00010001,
  0b00010001, 
  0b00010001

  You can see the arrangement of 1s in the above array forms the character 'A'. The complete text is displayed in a row scanning mode where each row is scanned for a very short amount of time and the columns are fed with a the appropriate bytes. By quickly scanning across the rows, and turning on the respective LEDs in each column of that row, the persistence of vision comes in to play, and we perceive the displayed image as still.

  A buffer variable is maintained which stores the characters currently displayed.

  unsigned int DisplayBuffer[][8] = {{0, 0}, {0, 0}, {0, 0}, {0, 0}, {0, 0}, {0, 0}, {0, 0}, {0, 0}}; 

  To scroll the text this buffer variable is shifted left after every few milliseconds and new data is fed into the buffer from the right.

  if(Serial.available() > 0){
        message = Serial.readString();
     }
    StringLength = message.length() ;
  
    for (k = 0; k < StringLength; k++) {
      for (scroll = 0; scroll < (8 / shift_step); scroll++) {
        for (ShiftAmount = 0; ShiftAmount < 8; ShiftAmount++) {
  
          DisplayBuffer[0][ShiftAmount] <<= 1;
          if (DisplayBuffer[1][ShiftAmount] & 0x80) {
            DisplayBuffer[0][ShiftAmount] |= 1;
          }
  
          index = message[k];
          temp = pgm_read_byte_near(&Data[index - 32][ShiftAmount]);
          DisplayBuffer[1][ShiftAmount] = (DisplayBuffer[1][ShiftAmount] << shift_step) | (temp >> ((8 - shift_step) - scroll * shift_step));
        }
  
        speed = 10;
        for (l = 0; l < speed; l++) {
          for (i = 0; i < 8; i++) {
            write595(DisplayBuffer[0][i]);
            write595(DisplayBuffer[1][i]);
            delayMicroseconds(50);
            digitalWrite(rowPins[row], HIGH);
            delay(1);
            digitalWrite(rowPins[row], LOW);
            row++;
            if (row >= 8)
              row = 0;
          }
        }
      }
    }

  Two firmware boot on the first soldered board:
  

• First batch of the badge

  Nitesh Kadyan • 04/02/2018 at 04:44 • 0 comments

  Since I don't have a stencil hence soldering the first circit few board with hand. This board is getting diffused white leds.
  

  
  

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