Segmented Display for Bangla Numerals: Simplicity vs. Accuracy S. M. Niaz Arifin, Lenin Mehedy and M Kaykobad Department of Computer Science and Engineering, Bangladesh University of Engineering and Technology, Dhaka – 1000, Bangladesh. Emails: [email protected], [email protected], [email protected] Abstract: Numerals can be efficiently displayed using the segmented display method. This paper proposes two schemes to display Bangla numerals 0...9 that can be used in all sorts of electronic equipment. The proposed 10-segment scheme is an improvement over the previously proposed 11-segment scheme. It can be used when simplicity is preferred. The proposed 18segment scheme takes into account the special curved-edge characteristics of the Bangla numerals. It can be used when accuracy in appearance is the first preference. Both of these schemes can be suitably employed in lieu of dot matrix systems that need more complex logic, cost and memory space Keywords: Bangla Numerals, Segmented display, edges, combination vector. 1. Introduction Displays with finite number of segments for each numeric character are preferred to dot matrix displays because the former saves both in memory space and cost. To show English numerals, 7-segment display is used for long. Saber et al [8] proposed an 11segment display for Bangla digits. This paper proposes two methods to show Bangla numerals by the 10-segment display and the 18-segment display. The 10-segment display is a substantial improvement over the 11-segment display [8] in terms of the number of segments used, which in turn reduces the required combinational logic, memory space and also the cost if measured from the industrial production viewpoint. The shape and the overall outlook of each digit are also improved. This scheme can be used where simplicity is preferred. The 18-segment display can be chosen where accuracy in outlook of the numerals is the priority. 2. Characteristics of Bangla Numerals Unlike its English counterpart, each Bangla numeral has more curved corners that make the design of each segmented numeral a complicated task. The final appearance of each numeral heavily depends on the accuracy of implementing these curved corners with perfection. But we have observed that the number of segments needed to represent each numeral increases linearly with

the required degree of accuracy of the curved edges. So there lies a potential trade-off between simplicity of the design and accuracy of the final output. This is why two different schemes have been proposed to provide an option for the users. 3. The Proposed Architecture In order to minimize number of logic gates in the representation of segments in the numerals, we have used the Karnaugh map method. Minimization of number of segments was done by rigorous observation. Two schemes, namely 10-segment and 18segment displays, have been proposed considering simplicity and accuracy. The final appearances of the digits in both schemes are shown in Table 1 in two separate columns so that comparisons can be readily made. The circuit in Figure 1 is suitable for driving LED displays and is commonly used to illuminate English numerals [2][3]. The standard IC 7447 is used for this purpose. Figure 2 and Figure 3 shows the circuits for the 10-segment display and the 18-segment display, respectively [3]. The following principles have been used during the design phase of both the schemes, without affecting the basic shape of each Bangla numeral: No segment overlapping was allowed. It was tried to cover as many digits as possible by each segment. During the logic design phase, if more than one segment were found to be either on or off simultaneously, they were merged and treated as a single segment having at most one right angle bending or a bending having angle of 45° inside them, in order to reduce the number of total segments. As rounded or curved segments are still not available at low cost, none of them is used. Segments having one 45° or right angle bending were employed, as they are relatively cheap than the curved ones. Section 4 contains the combination vector for each digit, the truth table and simplified expression for each segment for the 10segment scheme. Section 5 contains the same for the 18-segment scheme.

Table 1: Appearance of individual digits in both schemes Digit

0

1

2

3

4

5

6

7

8

9

10-segment

18-segment

+5V o

+5V o

a

a f g

e

b

f gj

c

i

GND

A

a b c d e f g

VCC

7447

GND

B

c

C

d

150Ω each

Other inputs

150Ω Each o

h

e

d

VCC

b

Other inputs a b c d e f g h i j

o

IC1 A

D

B

C

D

BCD inputs

BCD inputs

Figure 1: Circuit for single 7- segment English numeral

Figure 2: Circuit for single 10- segment Bangla numeral

+5V o 10 1

17 13

2

9 11

18

8 15 6

14 16

7 12

5

3 4

Other inputs

150Ω each VCC

a1 .......................... a9 ............................. a18

o

GND

IC2 A

B

C

D

BCD inputs Figure 3: Circuit for single 18- segment Bangla numeral

A

B

C

D

A'C'

a A'B'D' A'BD

b

B'C'D A'B'

c

A'C'D' A'CD

d

A'D

e A'B

A'D'

f

B'C'

g B'C'D' AB'C'

h A'BC'D'

A'BCD

i A'B'CD'

A'C'D A'CD' A'BC'D

A'BCD'

Figure 4: Circuit Diagram for IC1

j

A B C

D

a1 A'B'CD

a2

A'BCD' AB'C'D'

a3

A'BC'D

a4

B'C'D A'C'

a5

B'C'

a6

A'B'D A'BD'

a7

B'C'D'

a8

A'BCD AB'C'D

a9

A'D

a10

A'B'C' A'BC

a11

AB'C' A'BC'D'

a12

A'B

a13

A'CD'

a14

A'B'

a15

A'CD A'C'D'

a16

A'B'D'

a17

A'BD A'B'CD'

a18

A'C'D

Figure 5: Circuit Diagram for IC2

Digits 0 1 2 3 4 5 6 7 8 9

A 0 0 0 0 0 0 0 0 1 1

BCD Inputs B C 0 0 0 0 0 1 0 1 1 0 1 0 1 1 1 1 0 0 0 0

D 0 1 0 1 0 1 0 1 0 1

Truth table for the 10-segment scheme Segments a b c d e f 1 1 1 1 1 1 1 1 1 1 1 0 1 1 0 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 0 0 1 1 1 1 1 1 1 0 0 1 0 0 0 0 1 1 1 1 1 0 1 0

g 0 1 1 0 1 0 0 1 1 1

h 0 1 1 0 1 1 1 1 1 1

i 0 0 0 0 0 0 0 0 1 0

a13 0 0 0 0 1 0 0 1 0 0

a14 0 1 1 0 1 0 0 1 1 1

j 0 0 0 0 0 1 1 0 0 0

Truth table for the 18-segment scheme Digits 0 1 2 3 4 5 6 7 8 9

A 0 0 0 0 0 0 0 0 1 1

BCD Inputs B C 0 0 0 0 0 1 0 1 1 0 1 0 1 1 1 1 0 0 0 0

D 0 1 0 1 0 1 0 1 0 1

a1 0 0 0 1 0 0 1 0 1 0

a2 1 0 0 1 0 1 1 0 1 0

a3 1 1 0 1 1 1 1 0 1 1

a4 1 1 0 1 1 1 1 0 1 0

a5 0 0 0 0 0 0 0 1 0 1

4. Scheme 1: The 10-segment display a. Combination vector for each digit 0* = { a, b, c, d, e, f }, 1 = { a, b, c, d, e, g, h }, 2 = { a, b, d, e, g, h }, 3 = { b, c, d, e, f }, 4 = { a, b, c, d, e, f, g, h }, 5 = { a, c, d, e, f, h, j }, 6 = { c, d, e, f, h, j }, 7 = { a, b, c, f, g, h }, 8 = { e, f, g, h, i }, 9 = { a, b, c, e, g, h }. *The digit here represents its Bangla counterpart. The right-hand side vector lists all segments needed to be ‘on’ to illuminate the particular digit.

a6 1 1 0 1 0 1 1 1 0 1

A7 0 1 0 0 1 0 0 0 1 1

a8 0 0 1 0 1 1 1 1 1 0

Segments a9 a10 a11 1 1 0 1 1 0 1 1 0 1 0 1 1 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0

a12 0 0 1 0 0 0 0 0 0 0

a15 0 1 1 0 1 1 1 1 1 1

A16 0 1 0 0 1 0 0 0 1 1

a17 1 0 0 0 1 1 0 1 0 0

a18 0 0 0 0 0 1 1 0 0 0

5. Scheme 2: The 18-segment display a. Combination vector for each digit: 0* = { a2, a3, a4, a6, a9, a10, a17 }. 1 = { a3, a4, a6,a7, a9, a10, a14, a15, a16 }. 2 = { a8, a9, a10, a12, a14, a15 }. 3 = { a1, a2, a3, a4, a6, a9, a11 }. 4 = { a3, a4, a7, a8, a9, a10, a13, a14, a15, a16, a17 }. 5 = { a2, a3, a4, a6, a8, a10, a11, a15, a17, a18 }. 6 = { a1, a2, a3, a4, a6, a8, a11, a15, a18 }. 7 = { a5, a6, a8, a9, a10, a13, a14, a15, a17 }. 8 = { a1, a2, a3, a4, a7, a8, a14, a15, a16 }. 9 = { a3, a5, a6,a7, a9, a10, a14, a15, a16 }. *The digit here represents its Bangla counterpart. The right-hand side vector lists all segments needed to be ‘on’ to illuminate the particular digit.

b. Minimized expression for each segment (obtained by the b. Minimized expression for each segment (obtained by the Karnaugh-map method) Karnaugh-map method) a = A'C' + A'B'D' + A'BD + B'C'D, a1 = A'B'CD + A'BCD' + AB'C'D', b = A'B' + A'C'D' + A'CD + B'C'D, a2 = B'C'D' + A'BC'D + A'B'CD + A'BCD', c = A'C' + A'D + A'B + B'C'D, a3 = A'C' + B'C' + A'B'D + A'BD', d = A'C' + A'B' + A'D', a4 = A'C' + B'C'D' + A'B'D + A'BD', e = A'C' + A'B' + A'D' + B'C', a5 = A'BCD + AB'C'D, f = A'B +A'C'D' + A'CD + B'C'D', a6 = A'D + A'B'C' + B'C'D + A'BC, g = B'C'D + AB'C' + A'BC'D' + A'BCD + A'B'CD', a7 = AB'C' + B'C'D + A'BC'D, h = A'B + A'C'D + A'CD' + AB'C', a8 = A'B + A'CD' + AB'C'D', i = AB'C'D', a9 = A'B' + A'CD + A'C'D' + B'C'D, j = A'BC'D + A'BCD' . a10 = A'C' + B'C'D + A'B'D' + A'BD, Figure 4 depicts the circuit diagram for all segments of the 10- a11 = A'B'CD + A'BCD' + A'BC'D, segment scheme. a12 = A'B'CD',

a13 = A'BC'D' + A'BCD, a14 = B'C'D + A'BCD + A'B'CD' + A'BC'D' + AB'C', a15 = A'B + AB'C' + A'C'D + A'CD', a16 = AB'C' + B'C'D + A'BC'D', a17 = A'C'D' + A'BD, a18 = A'BC'D + A'BCD'. Figure 5 depicts the circuit diagram for all segments of the 18segment scheme. Standard inverter, 2-input, 3-input and 4-input AND and OR logic gates were used as before. 6. Conclusion We have developed two schemes to show Bangla numerals. From the viewpoint of the number of segments needed for the design and also the final appearance, the 10-segment scheme is an improvement over the 11-segment scheme [8]. It can be efficiently used when simplicity is preferred. The 18-segment scheme takes into account the special curved-edge characteristics of the Bangla numerals. It can be used when accuracy in appearance is the first preference. There lies potential scope of improvement in the industrial field related to this particular technology. Both of these schemes can be suitably employed in lieu of currently used dot matrix systems that need more complex logic, cost and memory space.

References [1] Barry M Cook and Neil H White, Computer Peripherals, Third Edition, Edward Arnold, 2002. [2] Rudolf F. Graf, Encyclopedia of Electronics Circuits. [3] Douglas V. Hall, Microprocessors and Interfacing – Programming and Hardware, Second Edition, Ch. 9, Pg 267268, McGraw-Hill International, Inc., 1995. [4] Karnaugh, M., “A Map Method for Synthesis of Combinational Logic Circuits.” Trans. AIEE, Comm. and Electronics, Vol. 72, Part I (November 1953), Pg 593-599. [5] M. Morris Mano, Digital Logic and Computer Design, Ch. 3, Pg 72, Prentice-Hall, Inc., 2000. [6] Roger S. Pressman, Software Engineering. [7] Mohamed Rafiquzamman, Microprocessors and Microprocessor Based System Design, Second Edition, CRC Press. [8] Ahmed Yousuf Saber, Mamun Al Murshed Chowdhury, Suman Ahmed and Chowdhury Mofizur Rahman, “Designing 11-Segment Display for Bangla Digits”, in Proceedings of International Conference on Computer and Information Technology (ICCIT), Dhaka, Bangladesh, 2002. [9] Microprocessors Data Handbook, Revised Edition, BPB Publications, 2000.