Sensors: DS18B20

• 

  DS18B20 TO92 case

• 

  DS18B20 stainless steel tube with leads

File:DS18B20.pdf

1. Power supply range: 3.0V to 5.5V.
2. Operating temperature range: -55°C to +125°C (-67°F to +257°F).
3. Accuracy over the range of -10°C to +85°C: ±0.5°C.
4. No other components, uses 1-Wire Bus
5. TO-92 case or in encapsulated in stainless steel tube.
6. Output lead: red (VCC), yellow(DATA) , black(GND).

Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1-Wire bus

The readings from 3 devices thermally tied together are very stable and close to each other:

Tue Jul 10 12:39:58 EDT 2018
t=20750
t=20562
t=20625
Tue Jul 10 12:40:30 EDT 2018
t=20750
t=20562
t=20625
Tue Jul 10 12:41:03 EDT 2018
t=20750
t=20562
t=20625

Tue Jul 10 12:44:20 EDT 2018
t=20750
t=20562
t=20625

List the devices on the bus

ls -l /sys/bus/w1/devices/

total 0
lrwxrwxrwx 1 root root 0 Jul 10 12:49 00-400000000000 -> ../../../devices/w1_bus_master1/00-400000000000
lrwxrwxrwx 1 root root 0 Jul 10 12:49 28-0317201a05ff -> ../../../devices/w1_bus_master1/28-0317201a05ff
lrwxrwxrwx 1 root root 0 Jul 10 12:49 28-03172025fdff -> ../../../devices/w1_bus_master1/28-03172025fdff
lrwxrwxrwx 1 root root 0 Jul 10 12:49 28-041720c6d4ff -> ../../../devices/w1_bus_master1/28-041720c6d4ff
lrwxrwxrwx 1 root root 0 Jul  9 22:09 w1_bus_master1 -> ../../../devices/w1_bus_master1

Note that 00-400000000000 is a "phantom" device.

Read a device

cat /sys/bus/w1/devices/28-03172025fdff/w1_slave|grep -Eo "t=\-*[0-9]{1,5}"

t=20875

Read all devices

# /bin/bash
#
PREFIX="/sys/bus/w1/devices/"
PREFIX_LEN=${#PREFIX};

DIRLIST=(${PREFIX}28*)

for FILENAME in ${DIRLIST[@]}
do
  DEVICE="${FILENAME:$PREFIX_LEN}";
  echo -n "$DEVICE "
  cat $FILENAME/w1_slave|grep -Eo "t=\-*[0-9]{1,5}"
done