A common method of indicating an error.

Representing Letters on a Seven-Segment Display, while highly discouraged, have been done mostly in low-end products such as cheap portable media players and many hobby projects. In such places, 7-segment displays were extended to support letters. Those representations varies from implementation to implementation and are not standardized by any standards organization.

Note that some letters such as K (), M (), V (), W (), X (), and Z () are completely unrecognizable by most people and as such been left out of the table below.

Digit	7-Segments							abcdefg	gfedcba	Display	Reference
	a	b	c	d	e	f	g
A	1	1	1	0	1	1	1	0x77	0x77
b	0	0	1	1	1	1	1	0x1F	0x7C
C	1	0	0	1	1	1	0	0x4E	0x39
c	0	0	0	1	1	0	1	0x0D	0x58
d	0	1	1	1	1	0	1	0x3D	0x5E
E	1	0	0	1	1	1	1	0x4F	0x79
F	1	0	0	0	1	1	1	0x47	0x71
G	1	0	1	1	1	1	0	0x5E	0x3D
H	0	1	1	0	1	1	1	0x37	0x76
h	0	0	1	0	1	1	1	0x17	0x74
I	0	0	0	0	1	1	0	0x06	0x30
J	0	1	1	1	1	0	0	0x3C	0x1E
L	0	0	0	1	1	1	0	0x0E	0x38
n	0	0	1	0	1	0	1	0x15	0x54
O	1	1	1	1	1	1	0	0x7E	0x3F
o	0	0	1	1	1	0	1	0x1D	0x5C
P	1	1	0	0	1	1	1	0x67	0x73
q	1	1	1	0	0	1	1	0x73	0x67
r	0	0	0	0	1	0	1	0x05	0x50
S	1	0	1	1	0	1	1	0x5B	0x6D
t	0	0	0	1	1	1	1	0x0F	0x78
U	0	1	1	1	1	1	0	0x3E	0x3E
u	0	0	1	1	1	0	0	0x1C	0x1C
y	0	1	1	1	0	1	1	0x3B	0x6E

Lookup table

One can decode letters to pins via a simple lookup table.

const unsigned char seven_seg_digits_decode_abcdefg[75]= {
/*  0     1     2     3     4     5     6     7     8     9     :     ;     */
    0x7E, 0x30, 0x6D, 0x79, 0x33, 0x5B, 0x5F, 0x70, 0x7F, 0x7B, 0x00, 0x00, 
/*  <     =     >     ?     @     A     B     C     D     E     F     G     */
    0x00, 0x00, 0x00, 0x00, 0x00, 0x77, 0x00, 0x4E, 0x00, 0x4F, 0x47, 0x5E, 
/*  H     I     J     K     L     M     N     O     P     Q     R     S     */
    0x37, 0x06, 0x3C, 0x00, 0x0E, 0x00, 0x00, 0x7E, 0x67, 0x00, 0x00, 0x5B, 
/*  T     U     V     W     X     Y     Z     [     \     ]     ^     _     */
    0x00, 0x3E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
/*  `     a     b     c     d     e     f     g     h     i     j     k     */
    0x00, 0x00, 0x1F, 0x0D, 0x3D, 0x00, 0x00, 0x00, 0x17, 0x00, 0x00, 0x00, 
/*  l     m     n     o     p     q     r     s     t     u     v     w     */
    0x00, 0x00, 0x15, 0x1D, 0x00, 0x73, 0x05, 0x00, 0x0F, 0x1C, 0x00, 0x00, 
/*  x     y     z     */
    0x00, 0x3B, 0x00
};
const unsigned char seven_seg_digits_decode_gfedcba[75]= {
/*  0     1     2     3     4     5     6     7     8     9     :     ;     */
    0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F, 0x00, 0x00, 
/*  <     =     >     ?     @     A     B     C     D     E     F     G     */
    0x00, 0x00, 0x00, 0x00, 0x00, 0x77, 0x00, 0x39, 0x00, 0x79, 0x71, 0x3D, 
/*  H     I     J     K     L     M     N     O     P     Q     R     S     */
    0x76, 0x30, 0x1E, 0x00, 0x38, 0x00, 0x00, 0x3F, 0x73, 0x00, 0x00, 0x6D, 
/*  T     U     V     W     X     Y     Z     [     \     ]     ^     _     */
    0x00, 0x3E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
/*  `     a     b     c     d     e     f     g     h     i     j     k     */
    0x00, 0x00, 0x7C, 0x58, 0x5E, 0x00, 0x00, 0x00, 0x74, 0x00, 0x00, 0x00, 
/*  l     m     n     o     p     q     r     s     t     u     v     w     */
    0x00, 0x00, 0x54, 0x5C, 0x00, 0x67, 0x50, 0x00, 0x78, 0x1C, 0x00, 0x00, 
/*  x     y     z     */
    0x00, 0x6E, 0x00
};

/* Invalid letters are mapped to all segments off (0x00). */
unsigned char decode_7seg(unsigned char chr)
{ /* assuming implementation uses ASCII */
    if (chr > (unsigned char)'z')
        return 0x00;
    return seven_seg_digits_decode_abcdefg[chr - '0'];
    /* or  seven_seg_digits_decode_gfedcba */
}