ASCII to 6-bit lookup table?

Projects Programming
1

Hi,

I've got a NYSE LED ticker that I finally figured out how to write characters to. It uses a 6-bit character code at 134.5 bits per second. I haven't figured out how to make Serial write to it, but I can bit-bang it.

I need help understanding how to convert ASCII characters to the character codes. Do I need a lookup table or what, and what should that look like.

Here is the table for the characters:

0x00		Undef
0x10		T
0x20		Figure D
0x30		1/8

0x01		E
0x11		Z
0x21		5
0x31		7/8

0x02		Letter Dot
0x12		L
0x22		C
0x32		S/S

0x03		A
0x13		W
0x23		1
0x33		1/2

0x04		Pr
0x14		H
0x24		Figure Dot
0x34  		8

0x05		S  
0x15		Y
0x25		S
0x35		3/4

0x06		I
0x16		P
0x26		9
0x36		S/T

0x07		U
0x17		Q
0x27		Spare 1/
0x37		1/4

0x08		WI
0x18		O
0x28		0     
0x38		Spare Figure Dot

0x09		D
0x19		B
0x29		4
0x39		2

0x0A		R
0x1A		G
0x2A		End Announcement Char
0x3A7

0x0B		J
0x1B		&
0x2B		Begin Announcement Char
0x3BB

0x0C		N
0x1C		M
0x2C		Space 
0x3C		$

0x0D		F
0x1D		X
0x2D		6
0x3D		5/8

0x0E		C
0x1E		V
0x2E		3
0x3E		3/8

0x0F		K
0x1F		R/T
0x2F		Spare Figure Dot
0x3F		Undef

And here is what my sketch for HELLO WORLD looks like:

int interval = 7;
int charDelay = 1;

char myText[]={0x14, 0x01, 0x12, 0x12, 0x18, 0x2C, 0x13, 0x18, 0x0A, 0x12, 0x09, 0x2C};

void setup() {
  pinMode(1, OUTPUT);
}

void loop(){
   for (int i = 0; i < 12; i ++){
     displayChar(myText[i]);
   }
}

void displayChar(byte charToDisplay){
  startBit();
    for (byte i = 0; i < 6; i ++){
      byte myBit = bitRead(charToDisplay, i); // the letter C 0r 001110  
      digitalWrite(1, myBit);
      delay(interval);
    }
    stopBit();
}

void stopBit(){            // two intervals of stop bit
  digitalWrite(1, LOW);
  delay(interval);
  delay(interval);
  digitalWrite(1, HIGH);
}

void startBit(){         // one interval for start bit
  digitalWrite(1, LOW); 
  delay(interval);
  digitalWrite(1, HIGH);
}

I plan to use a computer to send serial data to the ticker over an HC-05 bluetooth serial module from maybe a Raspberry Pi or other computer. Maybe I should do the data conversion on the sending side? Any pointers for doing that in Python also appreciated.

Thanks,

Jimmy

2

If you can find the logic for the conversion, you do not need a lookup table. Else you need one.

3

I would use two lookup tables. One for the alphabetic chars and one for the numerics. There aren't enough punctuation symbols to warrant a lookup table.

char alpha_6bit[26] = {
	0x03, //A
	0x19, //B
	// Fill in the rest of these
	...
	0x15, //Y
	0x11, //Z
};

char num_6bit[10] = {
	0x28 //0
	// Fill in the rest of these
	...
	0x26 //9
};

// Translate the ASCII character c to a 6-bit code.
// If the character is not found, return zero.
char ASCII_6bits(char c)
{
	c = toupper(c);
	if((c >= 'A') && (c <= 'Z'))return alpha_6bit[c - 'A']);
	if((c >= '0') && (c <= '9'))return num_6bit[c - '0']);
	// Handle the remaining punctuation characters
	if(c == ' ')return 0x2C;
	if(c == '

Pete)return 0x3C;
if(c == '&')return 0x1B;
return 0;
}


Pete
4

Thanks for the info, Pete. Can you show an example of how you access the array in the case you show? If I want to get 'A' (0x03), how do I reference the index? Do I just count because I know 'A' is 0 and 'B' is 1?

Or maybe subtract 0x41 to turn ASCII "A" into "0" for the index?

I was looking at the python side and found the Dict structure, which makes the conversion somewhat easy.

myChars = {	'N/A': 0x00,
          	'T':0x10,
          	'FIG DOT':0x20,
           	'1/8':0x30,
           	'E':0x01 ,
           	'Z':0x11 ,
           	'5':0x21 ,
           	'7/8': 0x31,
           	'LET DOT':0x02,
           	'L':0x12 ,
           	'C':0x22,
           	'S/S':     0x32,
           	'A':0x03,
		'W':0x13 ,
		'1':0x23,
		'1/2':0x33,
		'Pr':0x04,
		'H':0x14,
		'FIG DOT':0x24,
  		'8':0x34 }

and then I can do something like:

print hex(myChars['T'])

to get 0x10

Thanks for looking.

5

The ASCII_6bits function does the translation for you. Just call it for each character. For example:

Serial.println(ASCII_6bits(' '),HEX);

will print 2C.

Pete

6

Thanks Pete. I didn't see the ASCII_6bits(), I didn't scroll the block far enough!

Thanks.

Jimmy
7

Thanks so much for this help Pete! It was perfect and my stock ticker is ticking once again!

Karma and many thanks!