4 DIGIT DISPLAY FROM AN ALARM CLOCK:
I did something similar, but I didn't need any resistors or shift registers.
I bought an alarm clock at a thrift store and took out the LED display. There were 15 wires coming out the back. By using a 5v wire and a Ground wire I was able to figure out the High/Low combinations on the different wires that would turn on different segments. It turns out that setting 1 HIGH and 2 LOW will allow half of the segments to be lit by setting other pins high, then doing the opposite and setting 1 LOW and 2 HIGH will allow the other half to be illuminated.
Then I connected each wire directly to an arduino pin and turned it into a countdown timer.
// Press a button to increase the starting minutes, then wait for
// 5 seconds and the countdown begins
int i=0;
int seconds=0;
int minutes=8;
int tens;
int ones;
int go=0;
char var=0;
int state;
int lastState;
int single;
int minutes1;
long now;
unsigned long then;
long timer=360000;
void setup() {
pinMode(2,INPUT);
pinMode(4,OUTPUT);
pinMode(5, OUTPUT);
pinMode(6, OUTPUT);
pinMode(7, OUTPUT);
pinMode(8,OUTPUT);
pinMode(9,OUTPUT);
pinMode(10, OUTPUT);
pinMode(11, OUTPUT);
pinMode(12, OUTPUT);
pinMode(13,OUTPUT);
pinMode(14, OUTPUT);
pinMode(15, OUTPUT);
pinMode(16, OUTPUT);
pinMode(17, OUTPUT);
pinMode(18,OUTPUT);
pinMode(19, OUTPUT);
// Using Serial.begin(9600) makes pin 1 stay HIGH for some reason
//Serial.begin(9600);
}
void loop()
{
// This part starts the timer after a button press
if(go==0){
now=millis();
state=digitalRead(2);
if(state==0 && state != lastState){
minutes++; //increase starting minutes every time it's pressed
timer=now;
}
lastState=state;
if(now - timer > 4000){
go=1; // START THE COUNTDOWN
}
}
// This counts the seconds and minutes
if (go==1)
{
now=millis();
if(now-then > 1000){
seconds--; //count down the seconds
then=now;
/*
Serial.print("Seconds: ");
Serial.println(seconds);
Serial.print("Minutes: ");
Serial.println(minutes);
Serial.println();
Serial.print("tens: ");
Serial.println(tens);
Serial.print("Ones: ");
Serial.println(ones);
*/
}
if(seconds<0){
minutes--;
seconds=59;
if(minutes<0){
seconds=0;
}
}
}
if(minutes>10){
single=1;
minutes1=minutes-10;
} else{
single=0;
minutes1=minutes;
}
tens= seconds/10; //This gives the 10's digit
ones= seconds-(tens*10); //The last digit
//FIRST NUMERAL ON THE DISPLAY
BlueFunction();
delay(5);
RedFunction();
delay(5);
}
//-----------------------------------------------------------
// THIS LIGHTS UP THE DISPLAY BY SETTING DIFFERENT PINS
// HIGH OR LOW
void BlueFunction(){
digitalWrite(19,LOW); //SET ALL TWOS LOW (RED)
digitalWrite(18,HIGH);
digitalWrite(17,LOW);
digitalWrite(16,LOW);
digitalWrite(13,LOW);
digitalWrite(15,LOW);
digitalWrite(14,LOW);
digitalWrite(12,LOW);
digitalWrite(11,LOW);
digitalWrite(10,LOW);
digitalWrite(9,LOW);
digitalWrite(5,LOW);
digitalWrite(6,LOW);
digitalWrite(4,LOW);
digitalWrite(7,HIGH); //Colon : ??????????
//NOW LIGHT UP THE BLUES
// digitalWrite(8,HIGH); // Colon : ??????????????
if(minutes1==10){
digitalWrite(13,HIGH); //0
digitalWrite(14,HIGH);
digitalWrite(16,HIGH);
} else if(minutes1==9){
digitalWrite(13,HIGH);
digitalWrite(15,HIGH);
} else if(minutes1==8){
digitalWrite(13,HIGH);
digitalWrite(15,HIGH);
digitalWrite(14,HIGH);
digitalWrite(16,HIGH);
} else if(minutes1==6){
digitalWrite(13,HIGH);
digitalWrite(15,HIGH);
digitalWrite(14,HIGH);
digitalWrite(16,HIGH);
} else if(minutes1==5){
digitalWrite(13,HIGH);
digitalWrite(15,HIGH);
digitalWrite(14,HIGH);
} else if(minutes1==4){
digitalWrite(13,HIGH);
digitalWrite(15,HIGH);
} else if(minutes1==3){
digitalWrite(15,HIGH);
digitalWrite(14,HIGH);
} else if(minutes1==2){
digitalWrite(15,HIGH);
digitalWrite(14,HIGH);
digitalWrite(16,HIGH);
}
if(tens==0){ //BLUES
digitalWrite(11,HIGH);
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==9){
digitalWrite(11,HIGH);
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==8){
digitalWrite(11,HIGH);
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==7){
digitalWrite(11,HIGH);
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==6){
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==5){
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==4){
digitalWrite(11,HIGH);
digitalWrite(10,HIGH);
}else if(tens==3){
digitalWrite(11,HIGH);
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==2){
digitalWrite(11,HIGH);
digitalWrite(12,HIGH);
}else if(tens==1){
digitalWrite(11,HIGH);
digitalWrite(10,HIGH);
}
if(ones==9){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
}else if(ones==8){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
digitalWrite(9,HIGH);
digitalWrite(5,HIGH);
}else if(ones==6){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
digitalWrite(9,HIGH);
digitalWrite(5,HIGH);
}else if(ones==5){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
digitalWrite(5,HIGH);
}else if(ones==4){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
}else if(ones==3){
digitalWrite(4,HIGH);
digitalWrite(5,HIGH);
}else if(ones==2){
digitalWrite(4,HIGH);
digitalWrite(9,HIGH);
digitalWrite(5,HIGH);
}else if(ones==0){
digitalWrite(6,HIGH);
digitalWrite(9,HIGH);
digitalWrite(5,HIGH);
}
}
//-------------------------------------------------------------------------
//------------------------------------------------------------------
void RedFunction(){
digitalWrite(18,LOW); //set it to RED
digitalWrite(19,HIGH);
digitalWrite(7,LOW); //set Colon : Low
digitalWrite(13,LOW); //set blues low
digitalWrite(15,LOW);
digitalWrite(16,LOW);
digitalWrite(14,LOW);
digitalWrite(12,LOW);
digitalWrite(11,LOW);
digitalWrite(10,LOW);
digitalWrite(7,LOW);
digitalWrite(5,LOW);
digitalWrite(9,LOW);
digitalWrite(6,LOW);
digitalWrite(4,LOW);
if (single==1){
digitalWrite(17,HIGH);
digitalWrite(16,HIGH);
}
if (minutes1==10){
digitalWrite(17,HIGH);
digitalWrite(16,HIGH);
digitalWrite(13,HIGH);
digitalWrite(14,HIGH);
digitalWrite(15,HIGH);
} else if (minutes1==9){
digitalWrite(13,HIGH);
digitalWrite(14,HIGH);
digitalWrite(15,HIGH);
} else if (minutes1==8){
digitalWrite(13,HIGH);
digitalWrite(14,HIGH);
digitalWrite(15,HIGH);
} else if (minutes1==7){
digitalWrite(13,HIGH);
digitalWrite(14,HIGH);
digitalWrite(15,HIGH);
} else if (minutes1==6){
digitalWrite(13,HIGH);
digitalWrite(14,HIGH);
} else if (minutes1==5){
digitalWrite(13,HIGH);
digitalWrite(14,HIGH);
} else if (minutes1==4){
digitalWrite(14,HIGH);
digitalWrite(15,HIGH);
} else if (minutes1==3){
digitalWrite(13,HIGH);
digitalWrite(14,HIGH);
digitalWrite(15,HIGH);
} else if (minutes1==2){
digitalWrite(13,HIGH);
digitalWrite(15,HIGH);
} else if (minutes1==1){
digitalWrite(14,HIGH);
digitalWrite(15,HIGH);
}
if(tens==0){
digitalWrite(9,HIGH);
digitalWrite(10,HIGH);
digitalWrite(12,HIGH);
}else if(tens==9){
digitalWrite(11,HIGH);
digitalWrite(12,HIGH);
}else if(tens==8){
digitalWrite(9,HIGH);
digitalWrite(10,HIGH);
digitalWrite(11,HIGH);
digitalWrite(12,HIGH);
}else if(tens==6){
digitalWrite(9,HIGH);
digitalWrite(10,HIGH);
digitalWrite(11,HIGH);
digitalWrite(12,HIGH);
}else if(tens==5){
digitalWrite(10,HIGH);
digitalWrite(11,HIGH);
digitalWrite(12,HIGH);
}else if(tens==4){
digitalWrite(11,HIGH);
digitalWrite(12,HIGH);
}else if(tens==3){
digitalWrite(10,HIGH);
digitalWrite(11,HIGH);
}else if(tens==2){
digitalWrite(9,HIGH);
digitalWrite(10,HIGH);
digitalWrite(11,HIGH);
}
if (ones==0){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
digitalWrite(5,HIGH);
} else if (ones==9){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
digitalWrite(5,HIGH);
} else if (ones==8){
digitalWrite(6,HIGH);
digitalWrite(4,HIGH);
digitalWrite(5,HIGH);
} else if (ones==7){
digitalWrite(6,HIGH);
There's no room for the rest of the code, but hopefully you get the gist