Wishield + sensors.requestTemperatures() with ds18b20: 23 sec. to get a webpage

Projects Networking, Protocols, and Devices
1

Hi guys,

i have a little problem i'm not even able to understand...

I wrote this simple sketch to make my Arduino write on a web page a temperature from a ds18b20; it works fine but it takes about 23 seconds to open the page.... too long...

I've also tried to modify some part of the code and i found that is the "sensors.requestTemperatures();" in void loop that makes the web rendering so slow. Infact, if i remove it and assign a static value to the temperature the web page appears instantly.

Can somebody help me?

this is the code:

#include <WiServer.h>

#define WIRELESS_MODE_INFRA    1 
#define WIRELESS_MODE_ADHOC    2
#include <OneWire.h>
#include <DallasTemperature.h>

#define ONE_WIRE_BUS 8
#define TEMPERATURE_PRECISION 12

DeviceAddress sonda1={0X28, 0XAC, 0XF6, 0XA7, 0X03, 0X00, 0X00, 0XCE};



// Setup a oneWire instance to communicate with any OneWire devices (not just Maxim/Dallas temperature ICs)
OneWire oneWire(ONE_WIRE_BUS);

// Pass our oneWire reference to Dallas Temperature. 
DallasTemperature sensors(&oneWire);

//float tempC = sensors.getTempC(sonda1);

// Wireless configuration parameters —————————————- 
unsigned char local_ip[] = {192,168,1,120};    // IP address of WiShield 
unsigned char gateway_ip[] = {192,168,1,1};    // router or gateway IP address 
unsigned char subnet_mask[] = {255,255,255,0};    // subnet mask for the local network 
const prog_char ssid[] PROGMEM = {"Cisco Home 2,4 gHz"};        // max 32 bytes

unsigned char security_type = 3;    // 0 – open; 1 – WEP; 2 – WPA; 3 – WPA2

// WPA/WPA2 passphrase 
const prog_char security_passphrase[] PROGMEM = {"xxx"};    // max 64 characters

// WEP 128-bit keys 
// sample HEX keys 
prog_uchar wep_keys[] PROGMEM = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,	// Key 0
				  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,	// Key 1
				  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,	// Key 2
				  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00	// Key 3
				};

// setup the wireless mode 
// infrastructure – connect to AP 
// adhoc – connect to another WiFi device 
unsigned char wireless_mode = WIRELESS_MODE_INFRA;

unsigned char ssid_len; 
unsigned char security_passphrase_len; 
// End of wireless configuration parameters —————————————-


// This is our page serving function that generates web pages 
boolean sendMyPage(char* URL) { 
   
   // if (strcmp(URL, "/") == 0) { 
        // Use WiServer’s print and println functions to write out the page content 
        WiServer.print("<html>"); 
        WiServer.print("Temperatura: ");
        
        //WiServer.print(tempC);
        
        WiServer.print(sensors.getTempC(sonda1));
        
        WiServer.print("</html>"); 
        // URL was recognized 
        return true; 
    //} 
    // URL not found 
    return false; 
}



void setup() { 
  // Initialize WiServer and have it use the sendMyPage function to serve pages 
  WiServer.init(sendMyPage); 
  // Enable Serial output and ask WiServer to generate log messages (optional) 
  //Serial.begin(57600); 
  //WiServer.enableVerboseMode(true); 
 
  //Serial.begin(9600);
  sensors.begin();
  sensors.setResolution(sonda1, TEMPERATURE_PRECISION);
}

void loop(){
 
  sensors.requestTemperatures();
  WiServer.server_task(); 
 // delay(10); 
 
}
2

It takes 0.75 seconds for a DS18B20 to measure a temperature. It is not a good idea to gather the temperature every time through loop().

3

i supposed so... what can i do? adding a delay() in the loop will slow down much more the entire loop.... if i was able, i would make the arduino read the temp. every 10 seconds and store the value... but i don't know how to do it...

4

If the library you use allows it you can tell the DS18B20 to start a conversion and send a separate request for the result at least 750 milliseconds later.

To check every 10 seconds, without putting in a delay(), you can use the "BlinkWithoutDelay" example as a starting point.

void loop()
    {
    static unsigned long lastSampleTime = 0;
    if (millis() - lastSampleTime > 10000)  // Only after 10 seconds
         {
         lastSampleTime = millis();
         //get temperature again
         }
    }