4 digit 7 segments display wrong number

Question

I'm an Arduino newbie having problems with 4 digit 7 segments display. I want to display some thousands to 4 digit 7 segments display but it display only 0000. I want to receive data from serial with string. And display the data to 4 digit 7 segments display... So test make String = '2575'... but it's not work. What's wrong in my codes? Any suggestions here will be a great help. thanks

int segments[] = {A0, A1, A2, A3};
byte digits[10][7] =
{
 { 1,1,1,1,1,1,0 }, // 0
 { 0,1,1,0,0,0,0 }, // 1
 { 1,1,0,1,1,0,1 }, // 2
 { 1,1,1,1,0,0,1 }, // 3
 { 0,1,1,0,0,1,1 }, // 4
 { 1,0,1,1,0,1,1 }, // 5
 { 1,0,1,1,1,1,1 }, // 6
 { 1,1,1,0,0,0,0 }, // 7
 { 1,1,1,1,1,1,1 }, // 8
 { 1,1,1,0,0,1,1 } // 9
};
void setup() {
 Serial.begin(9600); 
 for(int i=2;i<10; i++) {
 pinMode(i, OUTPUT);
 }
 for(int i=0; i<4; i++) {
 pinMode(segments[i], OUTPUT);
 }
}
void loop() {
 String IncomingData = "2575";
 for(int i=0; i<4; i++) {
 digitalWrite(segments[i], LOW);
 int digit = atoi(IncomingData[i]);
 displayDigit(digit);
 delay(5);
 digitalWrite(segments[i], HIGH);
 } 
}
void displayDigit(int num){
 int pin = 2;
 for(int i=0;i<7;i++){
 digitalWrite(pin+i, digits[num][i]);
 }
}

• CrossRoads: Are you sure you have a common cathode display? Do you have current limit resistors on each segment pin? Also, why do you have int for everything, when byte is all that is needed for a 0,1 or 0 to 9? Try adding a Serial.print after this line int digit = atoi(IncomingData[i]); to see that digit is breaking out what you think it is.
• 김태정: use common anode display. and int number display very well like displayDigit(5) but the code did not work... thanks
• CrossRoads: Code is setup for common cathode; low on the cathode to select the digit, high on the segments to turn them on. If you are using common anode, then reverse the logic; high on the digit to select one, low on the segments to turn them on.
• Gerben: Change displayDigit(digit); to displayDigit(3); to see if the problem is in the string parsing, or in the led-displaying part.
• 김태정: displayDigit(3); works... string parsing problem... thanks

Answer 1

You call atoi() with a char. Parameter of atoi is const char*. To convert ASCII code of digit to the digit use

int digit = IncomingData[i] - '0'

• 김태정: i can't understand that... anyway apply IncomingData[i] - '0' ... it's not works... thanks
• Juraj: @김태정, int digit = IncomingData[i] - '0'
• Juraj: you do not know what is ASCII code? how characters are encoded? or you don't know why IncomingData[i] is char and can't be used with itoa?
• 김태정: woww@.@ it works! thanks a lot! How can I understand the theory...! Have a nice day!
• 김태정: how can i accept the answer?...