Reading multiple DS18B20 sensors

Some people have been asking for some Python code that can read multiple temperature sensors.
The following code will work for up to 10 sensors (maximum allowed under the kernel driver)



#!/usr/bin/env python

from os import path, listdir, system
from time import sleep


# Borrowing some elements from https://github.com/timofurrer/w1thermsensor/blob/master/w1thermsensor/core.py
THERM_SENSOR_DS18S20 = 0x10
THERM_SENSOR_DS1822 = 0x22
THERM_SENSOR_DS18B20 = 0x28
RESOLVE_TYPE_STR = {"10": THERM_SENSOR_DS18S20, "22": THERM_SENSOR_DS1822, "28": THERM_SENSOR_DS18B20}
BASE_DIRECTORY = "/sys/bus/w1/devices"
SLAVE_FILE = "w1_slave"

# function to find how many sensors are connected, works for 3 types of sensor
def get_available_sensors():
   types = [THERM_SENSOR_DS18S20, THERM_SENSOR_DS1822, THERM_SENSOR_DS18B20]
   is_sensor = lambda s: any(s.startswith(hex(x)[2:]) for x in types)
   return [(RESOLVE_TYPE_STR[s[:2]], s[3:]) for s in listdir(BASE_DIRECTORY) if is_sensor(s)]

# function to return the initial 2 letters of the device ID ("28" for DS18B20 sensors)
def slave_prefix(mytype):
   return "%s-" % hex(mytype)[2:]

# function that grabs the raw temperature data from a sensor, requires full path+filename
def read_temp_raw(device_file):
   f_1 = open(device_file, 'r')
   raw_reading = f_1.readlines()
   f_1.close()
   return raw_reading

# function that checks that the reading of a sensor was good and strips out the temperature
def read_temp(device_file):
   lines = read_temp_raw(device_file)
   while lines[0].strip()[-3:] != 'YES':
       time.sleep(0.2)
       lines = read_temp_raw(device_file)
   equals_pos = lines[1].find('t=')
   temp = float(lines[1][equals_pos+2:])/1000
   return temp

for sensor in get_available_sensors():
   sp = slave_prefix(sensor[0])
   sensorpath = path.join(BASE_DIRECTORY, sp + sensor[1], SLAVE_FILE)
   print("Sensor %s has a temperature %.3f" % (sensor[1], read_temp(sensorpath)))

2 thoughts on “Reading multiple DS18B20 sensors

  1. Brady

    Thanks for posting this, it is reading my sensors brilliantly!!

    I have Cacti reading S1 as i have put the serial number of it into the data input for the graph but now my next challenge is getting the output from the above script to show the readings on the same line as expected by poller.

    Thanks again for the help!

    Reply

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