DS18B20dvr 1.1

DS18B20 library/driver for Raspberry Pi using the w1_therm kernel driver

DS18B20 library/driver for Raspberry Pi using the w1_therm kernel driver

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This module provides a clean and mostly complete (*) API for DS18B20 temperature sensors using the w1_therm kernel driver. It also provides a command line interface for interactive dev/debug.

Supports:

• Reading temperatures
• Bulk parallel conversion of temperatures for all sensors on the bus
• Resolution setting and Alarm thresholds setting in scratchpad
• Setting and measuring actual conversion (temperature measurement) time
• Scratchpad save/restore to/from EEPROM
• Multiple w1 busses

(*) Not supported:

• Alarm search - I've not found any useful documentation for triggering an alarm search nor reading back the in-alarm sensor list. I'm happy to add the feature if I only knew how.
• 'features' register (conversion error check and poll for completion)
• async_io (just needs development)
• Other sensor models

Tested on Python 3.9.2 and kernel version 6.1.21-v7+ #1642 SMP Mon Apr 3 17:20:52 BST 2023, and should work on similar kernel versions since about 2020.

Do read the fine datasheet.

Command Line Interface and Demo

Once installed (pip install DS18B20), a cli tool is available. The cli tool provides some useful debug and configuration features (such as setting and permanently saving the resolution setting), and also a few demonstration cases (such as triggering a bulk/parallel conversion on multiple sensors and reading back their values).

$ DS18B20cli -h
usage: DS18B20cli [-h] [-m MODE] [-n NAME] [-r RESOLUTION] [-L TL] [-H TH] [-c CONV_TIME] [-v] [-V] [DeviceID]

DS18B20 driver and CLI/demo for Raspberry Pi

Modes:
    0:  Dump info for all sensors (-m 0)  (DeviceID is optional, ignored)
    1:  Get current temp (-m 1)
    2:  Read scratchpad (-m 2)
    3:  Get current resolution (-m 3)
    4:  Set resolution (-m 4 -r 9)
    5:  Get current alarm temps (-m 5)
    6:  Set alarm temps (-m 6 -L 20 -H 30)
    7:  Send bulk_convert_trigger (-m 7)
    8:  Save scratchpad to EEPROM (-m 8)
    9:  Restore EEPROM to scratchpad (-m 9)
    10: Get current conversion time (-m 10)
    11: Set conversion time or start measurement (-m 11 -c 1)
    12: Get parasitic/external power status (-m 12)

    20: Minimal example for README (-m 20)
    21: Demonstrate saving alarm/resolution to EEPROM and restoring (-m 21)
    22: Demonstrate bulk/parallel temperature conversions and sensor reads (-m 22)
1.1

positional arguments:
  DeviceID              ID of target device, eg 28-0b2280337113

optional arguments:
  -h, --help            show this help message and exit
  -m MODE, --mode MODE  Test mode select (default 0)
  -n NAME, --name NAME  Name of the sensor to be displayed (default DS18B20)
  -r RESOLUTION, --resolution RESOLUTION
                        Resolution value (9, 10, 11, or 12) to be set with --mode 4 (default 12)
  -L TL, --TL TL        TL alarm value (degrees C) to be set with --mode 6 (default -25)
  -H TH, --TH TH        TH alarm value (degrees C) to be set with --mode 6 (default 50)
  -c CONV_TIME, --conv-time CONV_TIME
                        Conversion time setting or trigger measurement operation  (default 0 - set to spec value)
  -v, --verbose         Print debug-level status and activity messages
  -V, --version         Print version number and exit

A Minimal Example

In its simplest form, to use this library simply declare (instantiate) a sensor using its ID then issue a read_temperature() call. The cli tool mode 20 demonstrates this:

    if args.mode == 20:                     # Minimal example for README
        sensor = DS18B20(args.DeviceID, args.name)
        logging.info (f"Current temperature for sensor {sensor.device_name} / {sensor.device_id}:  {sensor.read_temperature(tempunits='F'):7.3f} F")

... And resultant output:

$ DS18B20cli 28-0b228004203c --name "My_Sensor" --mode 20
INFO:root:Current temperature for sensor My_Sensor / 28-0b228004203c:   76.212 F

Useful for debug

Mode 2 calls read_scratchpad() which invokes a dump and parse of a sensor's return results register, w1_slave:

$ DS18B20cli 28-0b228004203c --name "My_Sensor" --mode 2 --verbose
DEBUG:root:28-0b228004203c / My_Sensor - w1_slave file content:
8b 01 3c 0f 7f ff 7f 10 6c : crc=6c YES
8b 01 3c 0f 7f ff 7f 10 6c t=24687
DEBUG:root:28-0b228004203c / My_Sensor - temperature code:  01 8b   24.688 C,   76.438 F,  297.837 K
DEBUG:root:28-0b228004203c / My_Sensor - High alarm limit:  3c      60 C,      140.000 F,  333.150 K
DEBUG:root:28-0b228004203c / My_Sensor - Low  alarm limit:  0f      15 C,       59.000 F,  288.150 K
DEBUG:root:28-0b228004203c / My_Sensor - Resolution:        7f      12
DEBUG:root:28-0b228004203c / My_Sensor - Sensor root directory:     /sys/bus/w1/devices/28-0b228004203c
DEBUG:root:28-0b228004203c / My_Sensor - Bus master root directory: /sys/bus/w1/devices/w1_bus_master1
INFO:root:['8b', '01', '3c', '0f', '7f', 'ff', '7f', '10', '6c', ':', 'crc=6c', 'YES']

Mode 0 (the default mode) invokes a similar dump for every sensor found on the host, across all w1 busses, and includes conversion time and external power status:

$ DS18B20cli 
DEBUG:root:
Sensor </sys/bus/w1/devices/28-0b228004203c> on bus master </sys/bus/w1/devices/w1_bus_master1>:
DEBUG:root:28-0b228004203c / DS18B20 - w1_slave file content:
8c 01 3c 0f 7f ff 7f 10 bc : crc=bc YES
8c 01 3c 0f 7f ff 7f 10 bc t=24750
DEBUG:root:28-0b228004203c / DS18B20 - temperature code:  01 8c   24.750 C,   76.550 F,  297.900 K
DEBUG:root:28-0b228004203c / DS18B20 - High alarm limit:  3c      60 C,      140.000 F,  333.150 K
DEBUG:root:28-0b228004203c / DS18B20 - Low  alarm limit:  0f      15 C,       59.000 F,  288.150 K
DEBUG:root:28-0b228004203c / DS18B20 - Resolution:        7f      12
DEBUG:root:28-0b228004203c / DS18B20 - Sensor root directory:     /sys/bus/w1/devices/28-0b228004203c
DEBUG:root:28-0b228004203c / DS18B20 - Bus master root directory: /sys/bus/w1/devices/w1_bus_master1
DEBUG:root:28-0b228004203c / DS18B20 - Current conversion time:   750
DEBUG:root:28-0b228004203c / DS18B20 - External power status:     1
DEBUG:root:
Sensor </sys/bus/w1/devices/28-0b2280337113> on bus master </sys/bus/w1/devices/w1_bus_master1>:
DEBUG:root:28-0b2280337113 / DS18B20 - w1_slave file content:
7a 01 3c 0f 7f ff 7f 10 08 : crc=08 YES
7a 01 3c 0f 7f ff 7f 10 08 t=23625
DEBUG:root:28-0b2280337113 / DS18B20 - temperature code:  01 7a   23.625 C,   74.525 F,  296.775 K
DEBUG:root:28-0b2280337113 / DS18B20 - High alarm limit:  3c      60 C,      140.000 F,  333.150 K
DEBUG:root:28-0b2280337113 / DS18B20 - Low  alarm limit:  0f      15 C,       59.000 F,  288.150 K
DEBUG:root:28-0b2280337113 / DS18B20 - Resolution:        7f      12
DEBUG:root:28-0b2280337113 / DS18B20 - Sensor root directory:     /sys/bus/w1/devices/28-0b2280337113
DEBUG:root:28-0b2280337113 / DS18B20 - Bus master root directory: /sys/bus/w1/devices/w1_bus_master1
DEBUG:root:28-0b2280337113 / DS18B20 - Current conversion time:   750
DEBUG:root:28-0b2280337113 / DS18B20 - External power status:     1

References

• https://www.analog.com/media/en/technical-documentation/data-sheets/DS18B20.pdf
• https://docs.kernel.org/w1/slaves/w1_therm.html
• https://docs.kernel.org/w1/w1-generic.html
• https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-driver-w1_therm

---

Links to classes, methods, and functions

• ds18b20
• read_temperature
• read_temperature2
• read_scratchpad
• get_resolution
• set_resolution
• get_alarm_temps
• set_alarm_temps
• copy_scratchpad
• recall_e2
• bulk_convert_trigger
• bulk_convert_status
• get_conv_time
• set_conv_time
• get_ext_power

---

Class DS18B20 (device_id, device_name='DS18B20') - DS18B20 library/driver for Raspberry Pi using the w1_therm kernel driver

Parameters

device_id (str)

• As listed in /sys/bus/w1/devices/, eg '28-0b228004203c'

device_name (str, default 'DS18B20')

• User friendly name for the sensor

Class variables

device_id (str)

• device_id from sensor instantiation

device_name (str, default 'DS18B20')

• device_name from sensor instantiation

sensor_path (Path)

• full pathlib path to the sensor directory

bus_master_path (Path)

• full pathlib path the w1 bus master for the sensor

---

read_temperature (tempunits='C') - Return the temperature from w1_slave file, with CRC check

DS18B20() class member function

Parameter

tempunits (str, default 'C')

• Must be 'C', 'F' or 'K', else ValueError is raised.

Returns

• (float) Read temperature in tempunits
• (int) -255: CRC_ERROR
• (int) -256: READ_ERROR
• Raises ValueError if tempunits is not valid

---

read_temperature2 (tempunits='C') - Return the temperature from temperature file. Used with bulk_convert_trigger().

DS18B20() class member function

If a bulk_convert_trigger() was previously executed, return the previously captured temperature, else take and return a new measurement.

Parameter

tempunits (str, default 'C')

• Must be 'C', 'F' or 'K', else ValueError is raised.

Returns

• (float) Read temperature in tempunits
• (int) -256: READ_ERROR
• Raises ValueError if tempunits is not valid

---

read_scratchpad () - Return the w1_slave file line 1. Forces a new temperature conversion.

DS18B20() class member function

With debug logging, logs full w1_slave file, temperature (bytes 0 & 1), TH and TL (bytes 2 & 3), and resolution in the config register (byte 4).

Returns

• (str) Just line 1 (9 bytes and CRC calc/confirmation) from the w1_slave file (not the second line which include 't=xxxxx')
• (int) -256: READ_ERROR

---

get_resolution () - Return the current resolution setting in the config register

DS18B20() class member function

Returns

• (int) Current resolution setting in the config register, eg 12

---

set_resolution (resolution) - Set the configuration register resolution field. Requires root privilege (sudo).

DS18B20() class member function

Parameter

resolution (int or str)

• 9, 10, 11, or 12

Returns

• (int) New resolution setting, eg 12

---

get_alarm_temps () - Return the current alarm settings

DS18B20() class member function

Returns

• (str) Current alarm settings pair, eg '-15 20'
• Values are degrees C

---

set_alarm_temps (TL, TH) - Set the alarm TL and TH registers. Requires root privilege (sudo).

DS18B20() class member function

Values must be between -55C and +125C. w1_therm sets TL to the lower of the two temps, TH to the higher.

Parameters

TL (int or str)

• Low temp alarm threshold in degrees C

TH (int or str)

• High temp alarm threshold in degrees C

Returns

• (str) The newly set alarm settings pair, eg '-15 20'
• Raises ValueError if TL or TH value is not valid or out of range

---

copy_scratchpad () - write scratchpad TH, TL, and resolution to EEPROM. Requires root privilege (sudo).

DS18B20() class member function

Returns

• None

---

recall_E2 () - Restore EEPROM TH, TL, and resolution to scratchpad. Requires root privilege (sudo).

DS18B20() class member function

Returns

• None

---

bulk_convert_trigger () - Trigger parallel temp conversions for all sensors on this sensor's bus.

DS18B20() class member function

Requires root privilege (sudo), or <chmod 666 /sys/bus/w1/devices/w1_bus_masterX/therm_bulk_read>. Note that the chmod must be redone after each boot.

Follow with calls to .read_temperature2() for each sensor on the bus.

Returns

• (int) 1 on successful trigger. Returns after the parallel conversion time of all sensors on the bus.
• (int) 0 if trigger was not successful
• (int) -1 if at least one sensor is still in conversion

---

bulk_convert_status () - Return the status of bulk/parallel sensor conversions and reading on this sensor's bus.

DS18B20() class member function

Returns

• (int) 1 if any sensor on this sensor's bus has not yet be read with read_temperature2()
• (int) 0 if all sensors on this sensor's bus have been read
• (int) -1 if at least one sensor is still in conversion

---

get_conv_time () - Return the current conversion time setting

DS18B20() class member function

Returns

• (int) Currently set conversion time in milliseconds, eg 750

---

set_conv_time (conv_setting) - Set the conversion time for temperature measurements. Requires root privilege (sudo).

DS18B20() class member function

Parameter

conv_setting (int or str)

• 0: Set the default conversion time from the datasheet based on the current resolution (eg 750ms for 12-bit resolution)
• 1: Trigger measurement of the actual required conversion time, and set future conversions to the measured time. Note that this value is guardbanded 20% higher than the actual measured time, and thus may be higher than the specification time.
• >1: Set conversion time to conv_setting, resolution milliseconds

Returns

• (int) Currently set conversion time in milliseconds as a result of the conv_setting operation

---

get_ext_power () - Return the external power status

DS18B20() class member function

Returns

• (int) 0: Parasitic powered
• (int) 1: Externally powered