Tuesday, March 18, 2014

Arduino–Day 5: 7 Segment Numeral Display

A quick & dirty library for displaying numbers on a 7 Segment Display.  I’m storing the segment patterns in an array at the same position – ordinal - as that of the number.  Thus, a pattern for ‘0’ (Pin 10 & Pin 4 off – Dot & Central bar) would be found at numbers[0].

Countdown on a 7 Seg Display
1. //Pin patterns for 0-9
2. int numbers[][8] =  {
3.     { 1, 1, 1, 0, 1, 1, 1, 0 },
4.     { 0, 0, 1, 0, 1, 0, 0, 0 },
5.     { 1, 1, 0, 0, 1, 1, 0, 1 },
6.     { 0, 1, 1, 0, 1, 1, 0, 1 },
7.     { 0, 0, 1, 0, 1, 0, 1, 1 },
8.     { 0, 1, 1, 0, 0, 1, 1, 1 },
9.     { 1, 1, 1, 0, 0, 1, 1, 1 },
10.     { 0, 0, 1, 0, 1, 1, 0, 0 },
11.     { 1, 1, 1, 0, 1, 1, 1, 1 },
12.     { 0, 1, 1, 0, 1, 1, 1, 1 },
13. };
14.
15. // Pin 1, 2, 4, 5, 6, 7, 9, 10 anti clockwise starting from lower left corner
16. int pins[] = {3, 4, 6, 7, 8, 9, 11, 12};
17.
18.
19.
20. void setup()
21. {
22.
23.   /* add setup code here */
24.
25. }
26.
27. void loop()
28. {
29.
30.   /* add main program code here */
31.
32.     for (int number = 9; number <= 0; number++)
33.     {
34.         displayNumber(number);
35.         //Wait 1 second
36.         delay(1000);
37.     }
38.
39.     //Display four random number
40.     for (int i = 1; i < 5; i++)
41.     {
42.         int next = random(0, 9);
43.         displayNumber(next);
44.         clear();
45.         delay(1000);
46.     }
47.
48.     delay(1000);
49. }
50.
51.
52. void displayNumber(int number)
53. {
54.     for (int i = 0; i < 8; i++)
55.     {
56.         //determine pin for the segment 0-7
57.         int pin = pins[i];
58.         bool pinOffOn = numbers[number][i];
59.
60.         pinMode(pin, OUTPUT);
61.         //Turn on the segment
62.         digitalWrite(pin, (pinOffOn) ? HIGH : LOW);
63.     }
64. }
65.
66.
67. void clear()
68. {
69.     for (int i = 0; i < 8; i++)
70.     {
71.         int pin = pins[i];
72.         pinMode(pin, OUTPUT);
73.         digitalWrite(pin, LOW);
74.     }
75. }

The above approach is cost prohibitive (number of pins needed to drive a 4 digit number is staggering).

Not knowing Arduino’s capabilities, I’m hypothesizing (speculating) thus:

1. Either:
• Arduino should be able to drive multiple outputs through a single pin
• One pin per digit... Possibly 2 pins for n-number of digits
2. Or:
• We can send multiple values through a single Arduino digital pin punctuated by a specific delay (say, 10 millisecond increments).
• A timer would measure the difference, and route power to appropriate segment
• Pros: One pin for each digit
3. Or:
• Identify the digit by a specific delay upfront (100 millisecond increments)
• Route to the right digit
• All subsequent power would be sent to the same digit (till it's reset by a specific delay)
• We can send multiple values through a single Arduino digital pin punctuated by a specific delay (say, 10 millisecond increments).
• A timer would measure the difference, and route power to appropriate segment
• Pros: One pin for the whole display

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