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I am working on an Arduino based temperature reader using a DS18B20 temperature IC. The display is a 4 digit 7 segment LED common anode display driven by a single 74HC595 shift register. Currently, it is setup to read a variable assigned with a number to test the display portion. It displays to the tenths decimal place I am having troubles trying to get rid of the leading zeros. When the variable 'tempF' is assigned a number such as 12.3, the display yields 012.3 and if the variable is assigned a number such as 1.2, the display will yield 001.2. At the same time, I was wanting to have it place a minus (-) sign when the number is less than zero. So far, the examples I'm finding on the web don't seem to match into the code I'm currently working with or don't work at all. I haven't been able to locate a sketch that seems to work for this type of setup. I have posted below, the code I am working with. The original code was obtained from the link provided in the sketch.

The sketch there does not provide the means of reading negative temps or suppress leading zeros.


   /*
 * www.pial.net/arduino-controlling-a-4-digit-seven-segment-display/
 */

//#include <OneWire.h>
//#include <DallasTemperature.h>

//#define ONE_WIRE_BUS 2

//OneWire oneWire(ONE_WIRE_BUS);
//DallasTemperature sensors(&oneWire);
//DeviceAddress insideThermometer;

const int ledPin =  13;// LED connected to digital pin 13
const int latchPin = 8;//Pin connected to ST_CP of 74HC595
const int clockPin = 9;//Pin connected to SH_CP of 74HC595
const int dataPin = 10;//Pin connected to DS of 74HC595

const int digitPins[4] = {
  3,4,5,6}; //pins to control the 4 common anode pins of the display

const byte digit[10] = //seven segment digit bits
{
  B00111111, //0
  B00000110, //1
  B01011011, //2
  B01001111, //3
  B01100110, //4
  B01101101, //5
  B01111101, //6
  B00000111, //7
  B01111111, //8
  B01101111, //9
//  B00000000, //all segments off
//  B01000000 //-
};

int digitBuffer[4] = {
  1};
int digitScan = 0;
int soft_scaler = 0;
float tempC, tempF;
int tmp;

void setup()   {                
  TCCR2A = 0;
  TCCR2B = (1<<CS21);
  TIMSK2 = (1<<TOIE2);
  TCNT2 = 0;
  Serial.begin(9600);

  pinMode(ledPin, OUTPUT); 
  for(int i=0;i<4;i++)
  {
    pinMode(digitPins[i],OUTPUT);
  }
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);  

//  sensors.begin();
//  sensors.getAddress(insideThermometer, 0);
}

ISR(TIMER2_OVF_vect) {
  soft_scaler++;
  if(soft_scaler==15)
  {
    refreshDisplay();
    soft_scaler = 0;
  }
};  

void refreshDisplay()
{
  for(byte k=0;k<4;k++)
  {
    digitalWrite(digitPins[k], LOW);
  }
  digitalWrite(latchPin, LOW);  
  shiftOut(dataPin, clockPin, MSBFIRST, B11111111);
  digitalWrite(latchPin, HIGH);
  delayMicroseconds(50);
  digitalWrite(digitPins[digitScan], HIGH); 

  digitalWrite(latchPin, LOW);
//  if (digitScan==3)
//  {
//    shiftOut(dataPin, clockPin, MSBFIRST, ~(digit[digitBuffer[digitScan]] | B00000000)); //inserting the blank
//    }
//    else
//  {
//    shiftOut(dataPin, clockPin, MSBFIRST, digit[digitBuffer[digitScan]]);
//  }

  if(digitScan==1)
  {
    shiftOut(dataPin, clockPin, MSBFIRST, ~(digit[digitBuffer[digitScan]] | B10000000)); //inserting the dot
  }
  else
  {
    shiftOut(dataPin, clockPin, MSBFIRST, ~digit[digitBuffer[digitScan]]);
  }
  digitalWrite(latchPin, HIGH);
  digitScan++;
  if(digitScan>3) digitScan=0;
}

void loop()                     
{ 
  digitalWrite(ledPin, HIGH);
  boolean sign = false;
  //sensors.requestTemperatures();
  //tempC = sensors.getTempC(insideThermometer);
  //tempF = DallasTemperature::toFahrenheit(tempC);
  //tmp = int(tempF*100);
  tempF = 0.2;
  tmp = int(tempF*10);

//   if (digitScan == 4 ){
//    shiftOut(dataPin, clockPin, MSBFIRST, ~(digit[digitScan] | B00000000)); //inserting the blank
//    }
//    else
//  {
//    shiftOut(dataPin, clockPin, MSBFIRST, digit[digitBuffer[digitScan]]);
//  }

//if (tmp < 0){
//sign = true;
//tmp = abs(tmp);
//}

//if (digitScan == 3) {
//  if (tmp < 0){
//    shiftOut(dataPin, clockPin, MSBFIRST, ~(digit[digitBuffer[digitScan]] | B01000000)); // outputs minus sign
//  }
//  else {
//    shiftOut(dataPin, clockPin, MSBFIRST, ~(digit[digitBuffer[digitScan]] | B00000000));
//   }

//  tmp = abs(tmp);
// }   
//  else if (digitScan == 3 && digit[digitScan-1] == 0) { // writing on the second display (tens; if there are none, outputs nothing)
//     shiftOut(dataPin, clockPin, MSBFIRST, ~(digit[digitBuffer[digitScan]] | B00000000));
//   }
//   else if (i == 2) { // writing on the third display, where decimal point is needed
//     shiftOut(data_pin, clk_pin, MSBFIRST, digit[digitBuffer[i-1]]);
//   }
//   else { // writing on "other" displays (in fact fourth display AND seecond display only if there are some tens)
//     shiftOut(data_pin, clk_pin, MSBFIRST, digit[digitBuffer[i-1]]);
//   }


  digitBuffer[3] = int(tmp)/1000;
  digitBuffer[2] = (int(tmp)%1000)/100;
  digitBuffer[1] = (int(tmp)%100)/10;
  digitBuffer[0] = (int(tmp)%100)%10;
  Serial.print("number assigned to the variable 'tmp' = ");
  Serial.println(tmp);
  Serial.print("number assigned to the variable 'tempF' = ");
  Serial.println(tempF);
  digitalWrite(ledPin, LOW);
  delay(500);
}

The commented out commands in the sketch were attempts to remove leading zeros and add a minus sign when needed but failed. I have also posted a schematic of the project as well. A 74HC595 was used in this manner to free up pins to be used later in a deep freezer project.

I am by no means an expert programmer but if anyone could help me out or provide some insight on how to solve this problem, it would be most appreciated.

Arduino temp reader

  • Please edit your question (click "edit") and mark the code as code. When including code in a stackexchange question or answer, first paste the code into the question or answer editing box; then in that editing box, highlight the code and press ctrl-k. Or highlight the code and click the {} icon in the toolbar at the top of the editing box. To highlight text click-drag across it or use the arrow keys while holding the shift key. – James Waldby - jwpat7 Mar 13 '17 at 8:11
  • First figure out how you would do it by hand. Then translate that into code. – Ignacio Vazquez-Abrams Mar 13 '17 at 8:13
  • @IgnacioVazquez-Abrams - For me, easier said than done. I've been trying to find answers to this for a very long time with no luck. That or I don't know what exactly to search for to find the answers. – Remembermyname Mar 13 '17 at 8:34
  • Remembermyname, I didn't downvote, merely commented, but if you hadn't fixed it, I might have downvoted tomorrow. Anyhow, I upvoted after you fixed the code formatting. Now your question has 1 upvote and 1 downvote. – James Waldby - jwpat7 Mar 13 '17 at 19:51
  • @jwpat7 You're right, it was while before I caught my own error and had to correct it. If I had seen it, I would probably have downvoted it as well. I apologize, I didn't mean to accuse. I've removed the unwarranted comment. – Remembermyname Mar 13 '17 at 21:40
1

Any way to get rid of leading zeros?

Sure but two conditions have to be true:

1) you have the font information for "blank"; you need to un-comment it in your code for that.

2) you need to get rid of leading zeros, after having calculated the display buffer.

  displayBuffer[0]=(displayBuffer[0]==0)?FONT_BUFFER:displayBuffer[0]; //eliminate leading zero for displayBuffer[0]
  displayBuffer[1]=((displayBuffer[1]==0) && (displayBuffer[0]==FONT_BUFFER))?FONT_BUFFER:displayBuffer[1];
  ...

edit:

here is an example implementation of the concept from above, on a PIC12F675 driving two HC595. The number to be displayed is "12" on a 4-digit display. Blanking done on the first three digits -> you can confirm that by looking at the value of the display buffer lRAM[4]. 0x11 is my blank designator.

The partial display of '1' is due to multiplexing. Code largely based on what I wrote here: https://dannyelectronics.wordpress.com/2017/03/03/driving-7-segment-leds/, modified to drive over HC595s.

enter image description here

it should work on any mcu with minimum changes.

edit 2: here is your code driving a CC display directly. the number to be displayed is 1.23, with the leading zeros in the most significant 2 digits taken out.

enter image description here

  • I was aware of the uncommenting parts. They were previous attempts that didn't work as explained earlier. I tried the code snip before the display portion with it changed to match the variables in the sketch but I'm not certain of 'FONT_BUFFER'. Please elaborate. – Remembermyname Mar 13 '17 at 19:02
  • Is there an example anywhere that utilizes this? I've been going in circles on google for far too long. As if it were some kind of state secret. :/ – Remembermyname Mar 13 '17 at 19:04
  • I mean, this looks like a fairly straight forward answer. I tried to add shiftouts to use the masks (albeit poorly) and of course, they don't work. I'm just not aware why. – Remembermyname Mar 13 '17 at 22:00
  • Well, this appears to be a microchip example. I'm certain that the principles are the same but I haven't been able to get this to work at all. – Remembermyname Mar 18 '17 at 9:27

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