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

Detailed Description

ID: ds18b20
Name: Programmable Resolution 1-Wire Digital Thermometer
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 TTL level UART (specifically through the UartOW MRAA context class) to provide access to a Dallas 1-wire bus. It is important to realize that the UART is only being used to provide an interface to devices on a Dallas 1-wire compliant bus.

A circuit like the following should be used for the UART interface (ASCII schematic - best viewed in a fixed monospace font):

-| U| (D1) A| TX—|<–+ R| | T| RX----—o-----—o >to 1-wire data bus -|

        Vcc
         |
         o------------+
         |            |
         R1           |
         |            o(+)

>1-wire---—o-----—o[DS18B20] o(-) | GND

D1 = 1N4148 R1 = 4.7K

The cathode of D1 is connected to the UART TX.

    cout << "Initializing..." << endl;
    // Instantiate an DS18B20 instance using the default values (uart 0)
    upm::DS18B20 sensor;
    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 2 seconds
    while (shouldRun) {
        // update our values for all of the detected sensors
        sensor.update(-1);
        // we show both C and F for temperature for the sensors
        int i;
        for (i = 0; i < sensor.devicesFound(); i++) {
            cout << "Device " << i << ": Temperature: " << sensor.getTemperature(i) << " C / "
                 << sensor.getTemperature(i, true) << " F" << endl;
        }
        cout << endl;
        upm_delay(2);
    }
    cout << "Exiting..." << endl;

Public Member Functions
	DS18B20 (int uart=DS18B20_DEFAULT_UART)

	~DS18B20 ()

void	init ()

void	update (int index=-1)

float	getTemperature (unsigned int index, bool fahrenheit=false)

void	setResolution (unsigned int index, DS18B20_RESOLUTIONS_T res)

void	copyScratchPad (unsigned int index)

void	recallEEPROM (unsigned int index)

int	devicesFound ()

std::string	getId (unsigned int index)

Protected Attributes
ds18b20_context	m_ds18b20

Constructor & Destructor Documentation

DS18B20 ( int uart = DS18B20_DEFAULT_UART )

DS18B20 object constructor

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.

Parameters

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

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~DS18B20 ( )

DS18B20 object destructor

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Member Function Documentation

void init ( )

Deprecated:: This method is deprecated. It's functionality is handled in the constructor now.

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

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float getTemperature	(	unsigned 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

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void setResolution	(	unsigned int	index,
		DS18B20_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

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void copyScratchPad ( unsigned 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).

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void recallEEPROM ( unsigned 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).

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