Description

I have covered few temperature sensors in the past eg- LM35, DHT11, DHT22 and also the internal temperature sensor of the STM32 itself. Today in this tutorial I am going to interface DS18B20 temperature sensor with STM32.

The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements and has an alarm function with non-volatile user-programmable upper and lower trigger points. Like DHT11 and DHT22, DS18B20 also communicates over a 1-Wire bus that by definition requires only one data line (and ground) for communication with the micro controller. Let’s see how to program a ds18b20 temperature sensor using STM32.

HOW TO

NOTE:- This code now works with STM32CUBEIDE and it uses TIMER to create delay in microsecond. If you don’t know how to do that, watch the video on my channel on YouTube.

I am going to skip the Cube mx setup process as it’s usual one only. I am using pin PA1 as the data pin for the sensor and controller is running at it’s maximum frequency. Also I am NOT going to use DWT library for the delay in microseconds, as it is shown in the Video. I am using TIMER for the delay purpose.

void delay (uint32_t us)
{
	__HAL_TIM_SET_COUNTER(&htim1,0);
	while ((__HAL_TIM_GET_COUNTER(&htim1))<us);
}

It will be included in the code when you download it below. We need to write few functions for the sensor. They are as follows..

In order for the sensor to work, we need to initialize it every time. According to the datasheet, the initialization is done by pulling the data pin LOW for 480 us and than reading the pin for the presence pulse sent by sensor. Here is the function for that

uint8_t ds18b20_init (void)
{
	gpio_set_output ();   // set the pin as output
	HAL_GPIO_WritePin (GPIOA, GPIO_PIN_1, 0);  // pull the pin low
	delay (480);   // delay according to datasheet

	gpio_set_input ();    // set the pin as input
	delay (80);    // delay according to datasheet

	if (!(HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1)))    // if the pin is low i.e the presence pulse is there
	{
		delay (400); // wait for 400 us
		return 0;
	}

	else
	{
		delay (400);  // wait for 400 us
		return 1;
	}
}

To write a BIT to the sensor, we need to perform some operation on the data line. To generate a Write 1, after pulling the 1-Wire bus low, the master must release the 1-Wire bus within 15µs. When the bus is released, the 5kΩ pullup resistor will pull the bus high.

To generate a Write 0 time slot, after pulling the 1-Wire bus low, the master must continue to hold the bus low for the duration of the time slot (at least 60µs).

void write (uint8_t data)
{
	gpio_set_output ();   // set as output

	for (int i=0; i<8; i++)
	{

		if ((data & (1<<i))!=0)  // if the bit is high
		{
			// write 1

			gpio_set_output ();  // set as output
			HAL_GPIO_WritePin (GPIOA, GPIO_PIN_1, 0);  // pull the pin LOW
			delay (1);  // wait for  us

			gpio_set_input ();  // set as input
			delay (60);  // wait for 60 us
		}

		else  // if the bit is low
		{
			// write 0

			gpio_set_output ();
			HAL_GPIO_WritePin (GPIOA, GPIO_PIN_1, 0);  // pull the pin LOW
			delay (60);  // wait for 60 us

			gpio_set_input ();
		}
	}
}

A read time slot is initiated by the master device pulling the 1-Wire bus low for a minimum of 1µs and then releasing the bus. After the master initiates the read time slot, the DS18B20 will begin transmitting a 1 or 0 on bus. It transmits a 1 by leaving the bus high and transmits a 0 by pulling the bus low. When transmitting a 0, the sensor will release the bus by the end of the time slot, and the bus will be pulled back to its high idle state by the pull-up resister.

uint8_t read (void)
{
	uint8_t value=0;
	gpio_set_input ();

	for (int i=0;i<8;i++)
	{
		gpio_set_output ();   // set as output

		HAL_GPIO_WritePin (GPIOA, GPIO_PIN_1, 0);  // pull the data pin LOW
		delay (2);  // wait for 2 us

		gpio_set_input ();  // set as input
		if (HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))  // if the pin is HIGH
		{
			value |= 1<<i;  // read = 1
		}
		delay (60);  // wait for 60 us
	}
	return value;
}

The following is the sequence for reading temperature from the ds18b20

check = ds18b20_init ();
write (0xCC);  // skip ROM
write (0x44);  // convert t

HAL_Delay (800);

ds18b20_init ();
write (0xCC);  // skip ROM
write (0xBE);  // Read Scratchpad

temp_l = read();
temp_h = read();
temp = (temp_h<<8)|temp_l;
temperature = (float)temp/16;
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Connections

Result

Check out the VIDEO Below
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DOWNLOAD

You can buy me a coffee sensor 🙂

download the CODE below

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Ilya
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Ilya

Hi!
This description very good, need attention read all material.
Simple code and algorithm usability peripheries, me like this site 🙂
Good Luck!

Luiz
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Luiz

Hi!! I like very very much your tutorials, thank you very much!!
It would be nice to have the correct source files for the ds18b20, as they are for i2c lcd. Could you, please, provide the files accordingly?
Many thanks and best regards!!
Luiz

Bruno
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Bruno

very good the text. I would like to know how to read more than one sensor on the same pin? That is possible with this code ?

Bruno
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Bruno

I would like to know how do I use more than one sensor on the same pin with these functions?

Samira
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Samira

Hi, thx for good projekt. Can you say me , how does work read function by Value? I have Problem with value |= 1<<i.
Value must be OR with (1<< i) and i must schift 1 bit to Right ?
THX

MOJTABA
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MOJTABA

I really appreciate what you are doing ..when I’m watching youtube tutorial and hear background music which is exclusive for your tutorial ..it makes me cheerfull ..because I am sure that it is going to work out..thanks for that, keep it on I learn a lot from you.

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