I cannot get my DS18B20 temperature sensor to work

NETMF & Gadgeteer
41

Pascal - please start a new thread. You’ll get much more attention.

42

Could you please tell me how to to start a new thread, I didn’t find it unfortunately.

43

Connect 5V to pin 3 of the DS18B20 and your problem should be solved

44

Yes it works now, thanks a lot for your help.
Next step connect more than one sensor on the bus…

45

Pascal - I meant start a new forum thread, not a NETMF code Thread object. Seems you figured it out already.

Welcome to the forum.

46

Ransomhall, well I only find the way to reply an existing topic, not the way to create a new one… Is there any “Post new topic” button somewhere ?

47

Go up a level to where you can see the list of all topics in a particular forum. Then there is a “New Topic” button.

48

Wouldn’t be much of a forum if we couldn’t create new topics ;D At the top of each forum is a New Topic button.

49

Get it, in my case I should have place it in Home > Forum > FEZ Rhino, Domino, Mini, Panda and USBizi
Thanks a lot for your help.

50

Hi Everybody, i have play arround with the DS1820 and i think that i found a bug in previous code exposed.
In fact, reading the DALAS Manufacturer documentation, i noticed that the temperature read through the 2 bytes read after the “Read Scratchpad” command shall be devided by 2 to get the result in Celsius:

 Ds1820Sensor.WriteByte(0xBE); // Read Scratchpad
ushort temp = Ds1820Sensor.ReadByte(); 
temp |= (ushort)(Ds1820Sensor.ReadByte() << 8);  
float Celcius = (float)(temp) * 0.5f;

There is an ever more precise method to get the temperature if you consider all the bytes that you could read from the ds1820:

 if (Ds1820Sensor.Reset())
{
	Ds1820Sensor.WriteByte(0x55); //Match ROM
        Ds1820Sensor.Write(address, 0, address.Length);
        Ds1820Sensor.WriteByte(0x44); //Start conversion
	
        while (Ds1820Sensor.ReadByte() == 0)
        {
		;
	}

	Ds1820Sensor.Reset();
	Ds1820Sensor.WriteByte(0x55); // Match ROM
	Ds1820Sensor.Write(address, 0, 8);
	Ds1820Sensor.WriteByte(0xBE); // Read Scratchpad


	ushort temp = Ds1820Sensor.ReadByte(); //LSB
	temp |= (ushort)(Ds1820Sensor.ReadByte() << 8);   // MSB

	ushort register = Ds1820Sensor.ReadByte(); 
	register |= (ushort)(Ds1820Sensor.ReadByte() << 8);   

	ushort reserved = Ds1820Sensor.ReadByte(); 
	reserved |= (ushort)(Ds1820Sensor.ReadByte() << 8);   

	byte countRemain = Ds1820Sensor.ReadByte(); 
	byte countPerC = Ds1820Sensor.ReadByte(); 
	byte CRC = Ds1820Sensor.ReadByte(); 

	float Celcius = (float)(temp) * 0.5f - 0.25f + (((float)countPerC - (float)countRemain) / (float)countPerC);

Be carefull about the cast in float.
Wrong positionning of the cast might truncate the result and introduce some errors.

I hope this will help …

Bye.

51

DGA2011,

First you sholud take care how your DS18B20 is configure, as temperature precision could be from 9 to 12 bits.
The simpless way I found to caluculate it (assum that you are on default 12 bits configuratiojn) is :

float temp=(Ds1820Sensor.ReadByte()|(Ds1820Sensor.ReadByte()<<8))*0.0625;

By default DS18B20 return Celsius temp, and this is not necessary an integer and it could be negative (from -55 to +125).

For information :
T° Precision Coef
9 bits 0.5
10 bits 0.25
11 bits 0.125
12 bits 0.0625

Rgds Pascal.