4 Digit 7 Segment Thermometer Help

Hi Guys,

So I decided I was going to start learning how to use 7 Segment Displays and shift registers. I am using a 74HC595 to control the anodes of a 4 digit 7 segment display. And 2N3904s for the Cathodes. and a Dallas DS18B20 temperature sensor.

However, I am having extreme flicker/timing issues with the display. here is the code I am using. Instead of the display normally updating it cycles through each Digit with a about one second delay before displaying the next digit. So it displays one digit at a time. I have read that DallasTemp library causes delays. But the display shouldn't have large delays in between numbers? So I am slightly confused. Can anyone help me out?

Thanks,

Austin

/*
* created by Rui Santos, http://randomnerdtutorials.com
* Temperature Sensor Displayed on 4 Digit 7 segment common anode
* 2013
*
* Modified by Austin Pauley for use with DS18B20
* 2015
*/


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


#define ONE_WIRE_BUS A0
OneWire ds(ONE_WIRE_BUS);
DallasTemperature sensors(&ds);
DeviceAddress insideThermometer;


const int digitPins[4] = {
  5,4,3,2};                 //4 common anode pins of the display
const int clockPin = 11;    //74HC595 Pin 11 
const int latchPin = 12;    //74HC595 Pin 12
const int dataPin = 13;     //74HC595 Pin 14
const byte digit[10] =      //seven segment digits in bits
{
  B11000000, //0
  B11111001, //4
  B10100100, //2
  B10110000, //3
  B10011001, //4
  B10010010, //5
  B10000010, //6
  B11111000, //7
  B10000000, //8
  B10010000  //9
};
int digitBuffer[4] = {
  0,0,0,0};
int digitScan = 0, flag = 0, soft_scaler = 0;
;
float  tempC, tempF;


void setup(){
  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);
  Serial.begin(9600);
  sensors.setResolution(9);

}




void updateDisp(){
  for (byte j = 0; j < 4; j++)
  digitalWrite(digitPins[j], LOW);
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, B11111111);
  digitalWrite(latchPin, HIGH);


  delayMicroseconds(100);
  digitalWrite(digitPins[digitScan], HIGH);


  digitalWrite(latchPin, LOW);


  shiftOut(dataPin, clockPin, MSBFIRST, digit[digitBuffer[digitScan]]);


  digitalWrite(latchPin, HIGH);
  digitScan++;
  if (digitScan>3) digitScan = 0;



}


float getTemp()
{
sensors.requestTemperatures();
tempF = sensors.getTempF(insideThermometer);
}
void loop(){
  int temp = (int)getTemp();


  digitBuffer[3] = int(temp) / 1000;
  digitBuffer[2] = (int(temp) % 1000) / 100;
  digitBuffer[1] = (int(temp) % 100) / 10;
  digitBuffer[0] = (int(temp) % 100) % 10;
  updateDisp();

}

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0 sftwrngnr over 10 years ago

First off, I would only update the display if the temperature has actually changed, otherwise, you're reloading and cycling the shift register constantly. You could simply retain the previous displayed temperature in a buffer, and then only shift in and modify the digits that need to be changed.
Secondly, you mention that it's slow. You're delaying 100 microseconds between writes to the display, so that is likely the culprit.

-Dan
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0 Former Member over 10 years ago in reply to sftwrngnr

I have tried what you stated, and it is noticeably faster, but I can still see it "scanning" the digits. I know that I shouldn't but cannot find out why?

/*
* created by Rui Santos, http://randomnerdtutorials.com
* Temperature Sensor Displayed on 4 Digit 7 segment common anode
* 2013
*
* Modified by Austin Pauley for use with DS18B20
* 2015
*/


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


#define ONE_WIRE_BUS A0
OneWire ds(ONE_WIRE_BUS);
DallasTemperature sensors(&ds);
DeviceAddress insideThermometer;


const int digitPins[4] = {
  5,4,3,2};                 //4 common anode pins of the display
const int clockPin = 11;    //74HC595 Pin 11 
const int latchPin = 12;    //74HC595 Pin 12
const int dataPin = 13;     //74HC595 Pin 14
const byte digit[10] =      //seven segment digits in bits
{
  B11000000, //0
  B11111001, //4
  B10100100, //2
  B10110000, //3
  B10011001, //4
  B10010010, //5
  B10000010, //6
  B11111000, //7
  B10000000, //8
  B10010000  //9
};
int digitBuffer[4] = {
  0,0,0,0};
int digitScan = 0, pastTemp = 0, currentTemp = 0;
;
float  tempC, tempF;


float getTemp()
{
  sensors.requestTemperatures();
  tempF = sensors.getTempF(insideThermometer);
}


void setup(){
  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);
  Serial.begin(9600);
  sensors.setResolution(9);
  currentTemp = (int)getTemp();
}




void updateDisp(){
  for (byte j = 0; j < 4; j++)
  digitalWrite(digitPins[j], LOW);
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, B11111111);
  digitalWrite(latchPin, HIGH);


  digitalWrite(digitPins[digitScan], HIGH);


  digitalWrite(latchPin, LOW);


  shiftOut(dataPin, clockPin, MSBFIRST, digit[digitBuffer[digitScan]]);


  digitalWrite(latchPin, HIGH);
  digitScan++;
  if (digitScan>3) digitScan = 0;



}




void loop(){

  Serial.println(currentTemp);
  currentTemp = (int)getTemp();
  if (pastTemp != currentTemp)
  {
  digitBuffer[0] = int(currentTemp) / 1000;
  digitBuffer[1] = (int(currentTemp) % 1000) / 100;
  digitBuffer[2] = (int(currentTemp) % 100) / 10;
  digitBuffer[3] = (int(currentTemp) % 100) % 10;
  pastTemp = currentTemp;
  }
  updateDisp();
}


























}

Is this what you wanted me to do?

-Austin

0 Robert Peter Oakes over 10 years ago in reply to Former Member

Thats a good start but the call to requestTemperatures is a blocking call and it does several things including reseting the one wire bus, initiating a start conversion on all connected devices and then waits for all conversions to complete, this can be quite a significant delay

A way around this is to set waitForConversion to false with a call to setWaitForConversion but you will have to repeatedly check isConversionAvailable to see if the conversion has completed

this can be integrated into the gettemp function by testing if conversion is complete first, if it is not then return the last value read, if it is complete then read the temperature into your holding variable and imediatly initiate a new conversion (Even if you dont need it yet as it will take a while to complete) as much as 750 - 1000mS and will be the reason for your scanning display issues as at the end of a scan there will be upto 750mS delay while it makes another reading from the temp sensor

this way your never waiting for the conversion to complete (Which is what your currently doing) which is a slow process on the temp sensors.
You could improve even more by moving the conversion to your buffer into the gettemp function too and only update the buffer when a conversion is complete
then the main Loop() simply calls gettemp, then update display, it will never know or care if a new conversion has happened, it will simply display the contents of the buffer[], the conversion to the temperature is also only done after a sucesful conversion

this is a half baked version of this where the sketch simply waits a set amount of time ather than testing for completion https://github.com/milesburton/Arduino-Temperature-Control-Library/blob/master/examples/WaitForConversion2/WaitForConversion2.pde

This example shows the difference in time for each method https://github.com/milesburton/Arduino-Temperature-Control-Library/blob/master/examples/WaitForConversion/WaitForConversion.pde

neither example actually checks for conversion to complete but it is a simple function to implement and the cpp library file has implementation you could use as part of its coding

there are other optimizations you could perform but "Baby Steps"

Hope this helps
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0 mcb1 over 10 years ago in reply to Robert Peter Oakes

This is the code I use to check the temperature using One wire.

The idea is to note when you send off the temperature read instruction, and then keep checking to see if 750/1000mS has passed.

If it has then go read it.

This example only sampled every 10 secs (Line 108)

Line 150 checks to see if it is time to read and Line 185 resets the timer.

/* 
based on Eric Tsai 
License: CC-BY-SA, https://creativecommons.org/licenses/by-sa/2.0/ 

Date: 29-09-2014 
File: eLDERmon_Temp.ino 
This sketch is for a wired Arduino w/ RFM69 wireless transceiver 
Sends sensor data (temp) back to gateway.
See OpenHAB configuration file. 

1) Update encryption string "ENCRYPTKEY" 
2) 
*/  
  
  
/* sensor 
node = 12 
device ID 
6 = 1262, 1263 = temperature, humidity 


**** connections *****
Moteino Pin assignments
   Pin D0  Rx
   Pin D1  Tx
   Pin D2  RFM69 D100
   Pin D3  
   Pin D4  
   Pin D5  
   Pin D6  
   Pin D7  Temp sensor DS18B20 data pin with 4k7 external pullup resistor to 3v3
   Pin D8  
   Pin D9  
   Pin D10  RFM69 SS
   Pin D11  RFM69 MOSI
   Pin D12  RFM69 MISO
   Pin D13  RFM69 SCK
   
   Program as an UNO.

*/  
  
  
  
//RFM69  --------------------------------------------------------------------------------------------------  
#include <RFM69.h>
#include <RFM69registers.h>  
#include <SPI.h> 
#include <OneWire.h>


#define NODEID        12    //unique for each node on same network  
#define NETWORKID     100  //the same on all nodes that talk to each other  
#define GATEWAYID     1  
//Match frequency to the hardware version of the radio on your Moteino (uncomment one):  
#define FREQUENCY   RF69_433MHZ  
//#define FREQUENCY   RF69_868MHZ  
//#define FREQUENCY     RF69_915MHZ  
#define ENCRYPTKEY    "eLDERmon12345678" //exactly the same 16 characters/bytes on all nodes!  
#define IS_RFM69HW    //uncomment only for RFM69HW! Leave out if you have RFM69W!  
#define ACK_TIME      30 // max # of ms to wait for an ack  
#define LED           9  // Moteinos have LEDs on D9  
#define SERIAL_BAUD   9600  //must be 9600 for GPS, use whatever if no GPS  
  
boolean debug = 0;  
  
//struct for wireless data transmission  
typedef struct {    
  int             nodeID;             //node ID (1xx, 2xx, 3xx);  1xx = basement, 2xx = main floor, 3xx = outside  
  int             deviceID;           //sensor ID (2, 3, 4, 5)  
  unsigned long   var1_usl;           //uptime in ms  
  float           var2_float;         //sensor data?  
  float           var3_float;         //battery condition?  
} Payload;  
Payload theData;  
  
char buff[20];  
byte sendSize=0;  
boolean requestACK = false;  
RFM69 radio;  
  
//end RFM69 ------------------------------------------  

//inputs
const int TempSensor = 7;                   // Tempsensor name
  
// DS18B20 Temperature chip i/o
OneWire ds(7);                     // TempSensor on pin 7
byte i;
byte present = 0;
byte data[12];
byte addr[8];
word TReading;
byte HighByte, LowByte;
int SignBit;  
  
  
//temperature / humidity  =====================================  

float tempValue_previous = 0;

// 6 = 1262, 1263 = temperature, humidity  
  
  
// timings  

unsigned long last_temperature_time;
int temperature_interval = 10000;         // 10 seconds
  
  
void setup()  
{  
  Serial.begin(9600);          //  setup serial  
  Serial.println("Serial Up");
  pinMode(TempSensor, INPUT);
  delay(500);
  Temp_init();
  
  //RFM69-------------------------------------------  
  radio.initialize(FREQUENCY,NODEID,NETWORKID);  
  #ifdef IS_RFM69HW  
    radio.setHighPower(); //uncomment only for RFM69HW!  
  #endif  
  radio.encrypt(ENCRYPTKEY);  
//  char buff[50];  
//  sprintf(buff, "\nTransmitting at %d Mhz...", FREQUENCY==RF69_433MHZ ? 433 : FREQUENCY==RF69_868MHZ ? 868 : 915);  
//  Serial.println(buff);  
  theData.nodeID = NODEID;  //this node id should be the same for all devices in this node  
  //end RFM--------------------------------------------  

   
  
  //initialize times  
 last_temperature_time = millis();
  
  
  //PIR sensor  
  Serial.println("Starting now");
  delay(500);
}  
  
void loop()  
{  
  unsigned long time_passed = 0;  

  //===================================================================  
  //device #6  
  //temperature / humidity  
  
  if (millis() - last_temperature_time > temperature_interval) 
    {
    
    //reset and setup the temp sensor for communicating
        ds.reset();
        ds.select(addr);
        ds.write(0x44,1);        // start a temp reading
        
        delay(1000);             // wait 1 sec for data to be present
        
        present = ds.reset();
        ds.select(addr);    
        ds.write(0xBE);          // Read Scratchpad in the temp sensor
    
      for ( i = 0; i < 9; i++)   // we need 9 bytes
      {
        data[i] = ds.read();     //read the 9 bytes of data for a temperature      
      }
      
      LowByte = data[0];                       // the first byte is the lowest
      HighByte = data[1];                      // second byte is the highest
      TReading = (HighByte << 8) + LowByte;
      SignBit = TReading & 0x8000;             // test most sig bit
      if (SignBit)                             // If its negative
      {
         TReading = (TReading ^ 0xffff) + 1;   // 2's comp 
      }
     
      float t = TReading *0.0625; 
      if (debug)
      {
        Serial.print("temp = ");
        Serial.println(t);
      }

        last_temperature_time = millis(); 

        // Check if any reads failed and exit early (to try again).  
        if (isnan(t))
        {  
          if (debug) Serial.println("Failed to read from temp sensor!");
          tempValue_previous =0;  
          return;  
        }
       
       if (t > (tempValue_previous + 0.1)|| (t < (tempValue_previous - 0.1)))
       // only send if not the same  
       {
            //send data  
            theData.deviceID = 6;  
            theData.var1_usl = millis();  
            //theData.var2_float = f;    // Fahrenheit 
            theData.var2_float = t;  
            theData.var3_float = 0;  
            radio.sendWithRetry(GATEWAYID, (const void*)(&theData), sizeof(theData));         
            tempValue_previous = t;
            if (debug)
            {
               Serial.println("SENDING temp");
               Serial.print("tempValue_previous = ");
               Serial.println(tempValue_previous);
            }
       }
        
       if (debug)  
        {  

            Serial.print("   Temp= ");
            Serial.print(t);
            Serial.println(" C");
            delay(1000);
        }
  
  }
  
  
} 
void Temp_init()
{
  
  if ( !ds.search(addr)) {
    Serial.print("No more addresses.\n");
    ds.reset_search();
    delay(250);
    return;
  }
  
  Serial.print("R=");
  for( i = 0; i < 8; i++) {
    Serial.print(addr[i], HEX);
    Serial.print(" ");
  }

  if ( OneWire::crc8( addr, 7) != addr[7]) {
      Serial.print("CRC is not valid!\n");
      return;
  }
  
  if ( addr[0] != 0x28) {
      Serial.print("Device is not a DS18B20 family device.\n");
      return;
  }
}

Mark

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