Instructables

Temperature Displayed on 4 Digit 7 segment (common anode)

Picture of Temperature Displayed on 4 Digit 7 segment (common anode)
IMG_0287.JPG
In this project I’ll display the temperature in a 4 digit 7 segment display (common anode).
The sensor is the cheapest you can find so actually the temperature changes pretty easily which makes the display to show always different temperatures. But the idea is to apply this code to other projects with 7 segment displays that I might do later. if you want to learn a bit more of 7 segment displays you can read more at this post I've made.

This project is great to learn more about:
  • Reading sensors (in this case temperature)
  • 7 segment displays (4 digit 7 segment displays)
  • 8 bit Shift Registers (74HC595)
  • Pratice wiring
and for more project and tips you can also check my website:
http://randomnerdtutorials.com/
You can see this project working right now:
 
Remove these adsRemove these ads by Signing Up

Step 1: Parts Required

Picture of Parts Required
  • 1x Arduino Uno
  • 1x Temperature Sensor (I’m using the LM335Z)
  • 1x 4 Digit 7 Segment Display (common anode)
  • 1x 74HC595 8 Bit Shift Register
  • 8x 220 Ohm Resistors
  • 1x 4700 ohm Resistor
  • 1x Breadboard (or  two)
  • Jumper Cables

Step 2: Schematics

Picture of Schematics
7 segment 4 digit common anode.png
images.jpg
IMG_0274.JPG
I think it's a bit hard to follow the yellow connections with this schematic.
So i recommend that you take a look at the 74HC595 pins and to the internal circuit diagram of the 4 digit 7 segment display (common anode).
So how does the yellow connections were made?
Basically  the pin 11 connects to the QA, the pin 7 to the QB and so one…

Step 3: Upload the Code

Picture of Upload the Code
You can find the code here: https://gist.github.com/ruisantos16/5419223

Step 4: Final Product

Picture of Final Product
Check this video to see the circuit in action!
you can also visit my website for more electronic projects, interesting news and tips


T
hanks for reading!
And make sure you follow me so you can be notified when I release my new projects! 
Raphango9 months ago
What if I'm using a common cathode 4 digit 7 segment? Does it changes the cirtuit/code very bad?
RuiSantos (author)  Raphango9 months ago
yeah it actually changes the code and the circuit a bit... but it's totally possible!
if you make a quick search you'll see the difference and what you have to change.

I hope this helps! thanks for commenting!
I have managed to do it! Take a look at my code:
/*
* created by Rui Santos, http://randomnerdtutorials.com
* ALTERED BY: Raphango
* Temperature Sensor Displayed on 4 Digit 7 segment common CATHODE
* 2013
*/
const int digitPins[4] = {7,6,5,4}; //4 common CATHODE pins of the display (inverted the pins order)
const int clockPin = 11;    //74HC595 Pin 11
const int latchPin = 12;    //74HC595 Pin 12
const int dataPin = 13;     //74HC595 Pin 14
const int tempPin = A0;     //temperature sensor pin
const byte digit[10] =      //seven segment digits in bits
{
  B00111111, //0
  B00000110, //1
  B01011011, //2
  B01001111, //3
  B01100110, //4
  B01101101, //5
  B01111101, //6
  B00000111, //7
  B01111111, //8
  B01101111  //9
};
int digitBuffer[4] = {0};
int digitScan = 0;
float tempC; //Deleted kelvin and farenheit

void setup(){               
  for(int i=0;i<4;i++)
  {
    pinMode(digitPins[i],OUTPUT);
  }
  pinMode(tempPin, INPUT);
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT); 
  pinMode(tempPin, INPUT);
  //Serial.begin(9600);
}

//writes the temperature on display
void updateDisp(){
  
  for(byte j=0; j<4; j++) {digitalWrite(digitPins[j], HIGH);} // Turns the display off. Changed to HIGH
  digitalWrite(latchPin, LOW); 
  shiftOut(dataPin, clockPin, MSBFIRST, B00000000);
  digitalWrite(latchPin, HIGH);

  delayMicroseconds(2);

  digitalWrite(digitPins[digitScan], LOW); //Changed to LOW for turning the leds on.

  digitalWrite(latchPin, LOW); 
  if(digitScan==2)
    shiftOut(dataPin, clockPin, MSBFIRST, (digit[digitBuffer[digitScan]] | B10000000)); //print the decimal point on the 3rd digit
  else
    shiftOut(dataPin, clockPin, MSBFIRST, digit[digitBuffer[digitScan]]);

  digitalWrite(latchPin, HIGH);

  digitScan++;
  if(digitScan>3) digitScan=0;
}


void loop(){
  tempC = analogRead(tempPin)*0.00488;  //multiplied for this conversion constant
  tempC = tempC*10000;
  digitBuffer[3] = int(tempC)/1000;
  digitBuffer[2] = (int(tempC)%1000)/100;
  digitBuffer[1] = (int(tempC)%100)/10;
  digitBuffer[0] = (int(tempC)%100)%10;
if (digitBuffer[0]>=5) {
digitBuffer[0] = 5;
}
else {
digitBuffer[0] = 0;
}
delay(4);
  updateDisp();
 
}


###########################
Here's a video too:
Do you have already discovered how to smooth the transitions of showed temperature? Its quite annoying to see that glittering all the time....
 
RuiSantos (author)  Raphango9 months ago
Awesome! thanks for trying my project...
I'm sorry I had a few issues with that code... and I don't know why I couldn't figure out how to smooth the transitions. but I agree with you... it's a bit annoying. In the meanwhile I've started some new projects and I've never had time again to upgrade that code... :(

Thanks again for trying my project.
Can I post it on my website?
(on this page: http://randomnerdtutorials.com/feedback)
Of course!
Feel free to use it.

About the flickering, I did some changes to the "delay" values, but all it does is lighting up one of the 4 digits each time at an eye perceivable speed.

What I thought about doing was slowing the "update" rate, but unsuccesfully, since I'm a begginer in the shiftOut thing... =P

Thanks again!
SudiartoHsu9 months ago
sir, what the code if i use lm 35?
RuiSantos (author)  SudiartoHsu9 months ago
I think my code will work for lm35... but i don't have time to write the code for you...
I'm sorry, I receive to many requests.
Good luck with your project!
rimar20001 year ago
What a good work!
RuiSantos (author)  rimar20001 year ago
Thanks!