DS18B20 Class Reference

API for the DS18B20 1-Wire Temperature Sensor. More...

Detailed Description

• ID: ds18b20
• Name: DS18B20 1-Wire Temperature Sensor
• Category: uart
• Manufacturer: maxim
• Connection: uart
• Link: https://www.sparkfun.com/products/11050

This driver supports, and was tested with, a DS18B20 with external power.

Multiple DS18B20 devices can be connected to this bus. This module will identify all such devices connected, and allow you to access them using an index starting at 0.

Parasitic power is not currently supported due to the very tight 10us limit on switching a GPIO properly to supply power during certain operations. For this reason, you should use external power for your sensors.

Setting the alarm values (Tl, Th) is also not supported, since this is only useful when doing a 1-wire device search looking for devices in an alarm state, a capability not yet supported in MRAA. In reality, this is trivial to handle yourself in your application.

This device requires the use of a UART to provide access to a Dallas 1-wire bus, via a new facility supported by MRAA (once the relevant PR is accepted), using the UartOW access class. It is important to realize that the UART is only being used to access and control a Dallas 1-wire compliant bus, it is not actually a UART device.

  cout << "Initializing..." << endl;

  // Instantiate an DS18B20 instance using the default values (uart 0)
  upm::DS18B20 sensor;

  // locate and setup our devices
  sensor.init();

  cout << "Found " << sensor.devicesFound() << " device(s)" << endl;
  cout << endl;

  // bail if we didn't find anything
  if (!sensor.devicesFound())
    return 1;

  // update and print available values every second
  while (shouldRun)
    {
      // update our values for the first sensor
      sensor.update(0);

      // we show both C and F for temperature for the first sensor
      cout << "Temperature: " << sensor.getTemperature(0)
           << " C / " << sensor.getTemperature(0, true) << " F"
           << endl;

      sleep(1);
    }

  cout << "Exiting..." << endl;

Data Structures
struct	sensor_info_t

Public Types
enum	CMD_T {   CMD_CONVERT = 0x44, CMD_WRITE_SCRATCHPAD = 0x4e, CMD_READ_SCRATCHPAD = 0xbe, CMD_COPY_SCRATCHPAD = 0x48,   CMD_RECALL_EEPROM = 0xb8, CMD_READ_POWER_SUPPLY = 0xb4 }
enum	CFG_BITS_T { CFG_RESOLUTION_R0 = 0x20, CFG_RESOLUTION_R1 = 0x40, _CFG_RESOLUTION_MASK = 3, _CFG_RESOLUTION_SHIFT = 5 }
enum	RESOLUTIONS_T { RESOLUTION_9BITS = 0, RESOLUTION_10BITS = 1, RESOLUTION_11BITS = 2, RESOLUTION_12BITS = 3 }

Public Member Functions
	DS18B20 (int uart=DS18B20_DEFAULT_UART)
	~DS18B20 ()
void	init ()
void	update (int index=-1)
float	getTemperature (int index, bool fahrenheit=false)
void	setResolution (int index, RESOLUTIONS_T res)
void	copyScratchPad (int index)
void	recallEEPROM (int index)
int	devicesFound ()
std::string	getId (int index)

Static Public Attributes
static const uint8_t	DS18B20_FAMILY_CODE = 0x28

Protected Attributes
mraa::UartOW	m_uart
int	m_devicesFound
std::map< int, sensor_info_t >	m_deviceMap

Constructor & Destructor Documentation

DS18B20

(

int

uart = DS18B20_DEFAULT_UART

)

DS18B20 object constructor

Parameters

uart	Default UART to use (0 or 1). Default is 0.

~DS18B20

(

)

DS18B20 object destructor

Member Function Documentation

void init

(

)

This method will search the 1-wire bus and store information on each device detected on the bus. If no devices are found, an exception is thrown. Once this function completes successfully, you can use devicesFound() to determine how many devices were detected. This method must be executed first before any others below.

void update

(

int

index = -1

)

Update our stored temperature for a device. This method must be called prior to getTemperature().

Parameters

index

The device index to access (starts at 0). Specify -1 to query all detected devices. Default: -1

float getTemperature	(	int	index,
		bool	fahrenheit = false
	)

Get the current temperature. update() must have been called prior to calling this method.

Parameters

index	The device index to access (starts at 0).
fahrenheit	true to return the temperature in degrees fahrenheit, false to return the temperature in degrees celsius. The default is false (degrees Celsius).

Returns

The last temperature reading in Celsius or Fahrenheit

void setResolution	(	int	index,
		RESOLUTIONS_T	res
	)

Set the device resolution for a device. These devices support 9, 10, 11, and 12 bits of resolution, with the default from the factory at 12 bits.

Parameters

index	The device index to access (starts at 0).
res	One of the RESOLUTIONS_T values

void copyScratchPad

(

int

index

)

Copy the device's scratchpad memory to the EEPROM. This includes the configuration byte (resolution).

Parameters

index

The device index to access (starts at 0).

void recallEEPROM

(

int

index

)

Copy the device's EEPROM memory to the scratchpad. This method will return when the copy completes. This operation is performed by the device automatically on power up, so it is rarely needed.

Parameters

index

The device index to access (starts at 0).

int devicesFound ( )

inline

This method will return the number of DS18B20 devices that were found on the bus by init().

Returns

number of DS18B20's that were found on the bus

std::string getId ( int  index )

inline

Return an 8 byte string representing the unique device ID (1-wire romcode) for a given device index.

Parameters

index

The device index to access (starts at 0).

Returns

8 byte string representing the 1-wire device's unique romcode.

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The documentation for this class was generated from the following files:

• /iotdk/jenkins/workspace/upm-doc-stable/src/ds18b20/ds18b20.hpp
• /iotdk/jenkins/workspace/upm-doc-stable/src/ds18b20/ds18b20.cxx