All posts for the month July, 2013

This is the final post on configuring 1-Wire for temperature monitoring. In Part 1 I got all of the wiring figured out.  Part 2 was all about gathering the data into a log format.

This post is about getting that data stored and then rendered into a graphical format.

The first thing I did was slightly refactor my gathering. I wrote a bash script that queries the sensors in order and logs them to the same log file as before, but also puts that data into a round-robin database (RRD).  That way later on I can graph the data any way I want.

The big requirement before this script is run is to have existing RRD files. I used a Perl script to create these RRD files. This script would need to be updated for each sensor:
#!/usr/bin/perl -w

use Time::Local;
use RRDp;

# Create the database
RRDp::start "/usr/bin/rrdtool";
RRDp::cmd "create Living_Room.rrd
-b 1373820664
-s 60
" ;

Building that specification for the RRD is a bit of a dark-art. Here is the best way I can explain the options.

  • The “-b 1373820664” is the earliest data point allowed into the RRD. It is in epoch form. I did this because I wanted to back-fill my log data. This is optional if you are starting your graph from scratch.
  • The “-s 60” option is the data interval time in seconds. The “DS:temp:GAUGE:180:U:U” is the data point to be entered – “temp” is a label on that data point so it can be easily queried later on.
  • The RRA blocks are repeated for AVERAGE, MIN, and MAX so I will only describe one. “RRA:AVERAGE:0.5:1:10080” tells the RRD to keep 10080 data rows with 1 step. Each step is 1 minute. This ends up being 7 full days of data. “RRA:AVERAGE:0.5:5:4032” is similar in that it keeps 4032 data rows, but this time with a step of 5. This ends up being 14 days of data on a 5 minute interval. “RRA:AVERAGE:0.5:30:1344” keeps 28 days of data on a 30 minute interval. And “RRA:AVERAGE:0.5:120:21900” keeps 1825 days of data (about 5 years) with a 2 hour interval.

All of this data will be stored in a file that is 879K. Not bad for 5 years of data.

Here is the new digitemp_gather script. This script runs every minute via a cronjob:

DIGITEMP_CONF="-c /etc/digitemprc"


# Function to call digitemp with a given sensor ID and location.
# Generates a log message in $LOGFILE
function ProcessSensor {

cur_date=$(date +"%Y/%m/%d %H:%M:%S")
dateEpoch=$(date -d "$cur_date" +%s)
cur_temp=$(/usr/bin/digitemp -t $sensor_id -q -c /etc/digitemprc -o%.2F)
echo $cur_date $sensor_location F: $cur_temp >> $LOGFILE

rrdtool update $RRD_PATH/$sensor_location.rrd $dateEpoch:$cur_temp

ProcessSensor 0 Attic
ProcessSensor 1 Garage
ProcessSensor 2 Living_Room
ProcessSensor 3 Master_Bedroom

Now your cronjob is filling your RRD and it also continues to update the log file. It is not useful to graph data until you have at least 15 or 30 minutes worth of data- so time for a break.

Assuming you now have a bunch of data stored in your RRDs, it is pretty easy to extract that data with rrdtool and graph it as a PNG. This script creates the graphs in a temporary directory and I run it every 15 minutes. In my case, the last step is to copy the graphs to my web host so I can see them wherever I am.


# Function that builds graphs for a specific sensor on a given interval
# Usage: CreateGraph Sensor_Name Interval
# Example: CreateGraph Living_Room hour
function CreateGraph {

rrdtool graph $GRAPHS_DIR/$png_file
-h 80 -w 600
–start -1$time_length –end now
-t "$sensor_name :: last $time_length"
-v "degrees F"
GPRINT:temp:AVERAGE:"Avg\: %6.1lf"
GPRINT:temp:MAX:"Max\: %6.1lf"
GPRINT:temp:MIN:"Min\: %6.1lf"
GPRINT:temp:LAST:"Current\: %6.1lf degrees F\n"
> /dev/null

# Remove all of the existing graphs and recreate the graphs directory
if [ -e $GRAPHS_DIR ] ; then
/bin/rm -rf $GRAPHS_DIR

# Build all of the graphs
CreateGraph Attic hour
CreateGraph Attic day
CreateGraph Attic week
CreateGraph Garage hour
CreateGraph Garage day
CreateGraph Garage week
CreateGraph Living_Room hour
CreateGraph Living_Room day
CreateGraph Living_Room week
CreateGraph Master_Bedroom hour
CreateGraph Master_Bedroom day
CreateGraph Master_Bedroom week

# Copy the graphs to my webhost
scp -q $GRAPHS_DIR/*.png

This is a continuation post documenting my installation of a 1-Wire Temperature monitoring system in my house. Part 1 can be found here.

Ultimately I want to monitor 5 different sensors in and around my house. However because I don’t feel like climbing around in my attic when it is well north of 100 degrees, I am only going to hook up four.

In my last post, I documented the process of hooking up a weatherproof sensor to a RJ-11 jack. While that works and will work well, I previously wired RJ-45 jacks for ethernet so I switched to that size wherever I could.

Next problem I had to solve is how to distribute the 1-Wire system to multiple plugs. I found this Leviton 1×9 Structured Telephone Module which is typically used to distribute phone services up to 9 plugs. Since 1-wire uses three wires, this will work great. It is a $20 part, but well worth it.

I wired up three RJ-45 plugs into about 18″ of four-wire phone wire and then punched the wires down into the telephone module. I could then use my Ethernet panel to connect the USB sensor and the two internal sensors. I then punched down one of the weatherproof sensors into the same block. Lastly, I soldered a final sensor to a longer length of four wire phone cord. I ran that cable up into my attic and zip tied it to an attic brace. After I punched it into the block and plugged my two internal sensors in, I was set to test the system.

First up is to run the initialization:
stevet@neon:$ sudo /usr/bin/digitemp_DS2490 -i
DigiTemp v3.5.0 Copyright 1996-2007 by Brian C. Lane
GNU Public License v2.0 –
Found DS2490 device #1 at 001/019
Turning off all DS2409 Couplers
Searching the 1-Wire LAN
28C092C80400000E : DS18B20 Temperature Sensor
2881D1C8040000EB : DS18B20 Temperature Sensor
28355AD90400003C : DS18B20 Temperature Sensor
287B69C7040000BD : DS18B20 Temperature Sensor
ROM #0 : 28C092C80400000E
ROM #1 : 2881D1C8040000EB
ROM #2 : 28355AD90400003C
ROM #3 : 287B69C7040000BD
Wrote .digitemprc

Four sensors! Awesome. Now how hot is it at all of these sensors:
stevet@neon:$ sudo /usr/bin/digitemp_DS2490 -i
DigiTemp v3.5.0 Copyright 1996-2007 by Brian C. Lane
GNU Public License v2.0 –
Found DS2490 device #1 at 001/019
2013/07/14 13:07:31 Sensor 0 F: 110.53
2013/07/14 13:07:32 Sensor 1 F: 91.51
2013/07/14 13:07:33 Sensor 2 F: 78.69
2013/07/14 13:07:34 Sensor 3 F: 79.93

A bit warm in my attic. But every sensor worked.

In my last post I created a /etc/digitemprc file that is used as part of my cronjob. That config needs to be modified with the current sensors. Just like the last post, I used the .digitemprc file created by the initialization and changed the log format.

Because I added three sensors and the order has changed, my digitemp_rename script needs to be updated as well. Here is the new version. Very similar to before, but it handles the new sensors:

sed -e “s/Sensor 0/Attic/” -e “s/#0 : 28C092C80400000E//”
-e “s/Sensor 1/Garage/” -e “s/#1 : 2881D1C8040000EB//”
-e “s/Sensor 2/Living_Room/” -e “s/#2 : 28355AD90400003C//”
-e “s/Sensor 3/Master_Bedroom/” -e “s/#3 : 287B69C7040000BD//”

While I was doing all of this work, I disabled the crontab. It would error out while sensors were disconnected and moving around anyway. I cleared the log file and re-enabled the cronjob to run every minute.

After a few minutes, this is what my log looks like:
2013/07/14 13:08:02 Attic F: 110.53
2013/07/14 13:08:03 Garage F: 91.51
2013/07/14 13:08:04 Living_Room F: 78.69
2013/07/14 13:08:05 Master_Bedroom F: 79.93
2013/07/14 13:09:02 Attic F: 110.75
2013/07/14 13:09:03 Garage F: 91.51
2013/07/14 13:09:04 Living_Room F: 78.69
2013/07/14 13:09:05 Master_Bedroom F: 79.93
2013/07/14 13:10:02 Attic F: 110.86
2013/07/14 13:10:03 Garage F: 91.51
2013/07/14 13:10:05 Living_Room F: 78.57
2013/07/14 13:10:06 Master_Bedroom F: 79.81

Everything looks good from a logging perspective.

Part 3 is to graph the data that I am gathering and see how things look visually over time.

I have an older house with not so good insulation and windows. It gets too hot in the summer and too cold in the winter. My furnace and AC have to work extra hard to maintain a decent environment.

Before I begin spending a lot of money on upgrades, I wanted to get a baseline of the environment.

1-Wire is a fairly simple system that lets you monitor temperature with various sensors spread around the house. It also has support to monitor humidity, but I am only doing temperature for now.

First thing you need is a One-Wire adapter for your computer. I picked up a USB model that I am hooking up to my linux server. It is model DS9490R that I got from Hobby Boards for about $40 shipped. I picked up 10 waterproof DS18B20 sensors from a Chinese seller on eBay for about $20 shipped.

The DSR9490R has a six pin RJ-11 connector, but the sensors have just three wires. I picked up some four-wire telephone wire and some empty RJ-11 plugs at Home Depot and then it was time to start wiring.

It took me quite a while to figure out the pin-out. There seemed to be a bunch of conflicting info so I did a bunch of test crimps and patch wiring. There are three important wires that matter, voltage, data, and ground. On the sensors voltage is red, data is yellow (on some it is white), and ground is black. For the RJ-11 connector, the layout is voltage on pin 1, the data feed is on pin 3, and the ground feed is on pin 4. If you look at the top of a RJ-11 connector with catch on top and the opening pointing away from you, the pins go from 1 to 6 from left to right.

I could not get the waterproof sensor wires to fit and crimp into the RJ-11 plugs I had, so I took three short lengths of wire stripped from a phone cord to make a tail that is a couple inches long. I then wound and soldered the sensor wires to the tail.

Now I have a sensor that will plug into the USB adapter. Time to test it!

There are two main ways to read data from the sensors. DigiTemp and OWFS. To start and debug I decided to use DigiTemp.

First up, install digitemp. I am on a CentOS box so I used this command:
stevet@neon:$ sudo yum install -y digitemp

Then I plugged in my USB adapter and checked /var/log/messages to make sure it connected. I started a tail and left it running:
stevet@neon:$ tail -f /var/log/messages

Then I plugged in the sensor to the USB adapter. If there is a wiring problem, you may see the USB device get disconnected. If so, check that your wiring is going into the correct pins. If it looks good, time to detect your sensor.
stevet@neon:$ /usr/bin/digitemp_DS2490 -i
DigiTemp v3.5.0 Copyright 1996-2007 by Brian C. Lane
GNU Public License v2.0 –
Found DS2490 device #1 at 001/016
Turning off all DS2409 Couplers
Searching the 1-Wire LAN
287B69C7040000BD : DS18B20 Temperature Sensor
ROM #0 : 287B69C7040000BD
Wrote .digitemprc

Look a sensor! Now run a query and make sure the sensor is giving back a temperature:
stevet@neon:~$ sudo /usr/bin/digitemp_DS2490 -a
DigiTemp v3.5.0 Copyright 1996-2007 by Brian C. Lane
GNU Public License v2.0 –
Found DS2490 device #1 at 001/016
Jul 13 18:03:53 Sensor 0 C: 25.94 F: 78.69

It is 25.94 Celsius and 78.69 Fahrenheit at my desk. Nice!

Now it is time to log this data over time. First, we want to copy the DigiTemp config file to a standard location so we can script the data gathering.
stevet@neon:~$ sudo cp .digitemprc /etc/digitemprc

If you look at that config file – you will see the one sensor listed along with the log format. The log format is OK, but it can be better. I commented out the exiting log format and added this one:
# LOG_FORMAT “%b %d %H:%M:%S Sensor %s C: %.2C F: %.2F”
LOG_FORMAT “%Y/%m/%d %H:%M:%S Sensor %s F: %.2F”

Sensor 0 is not a very clear sensor name. This sensor will be in my living room, so I wrote a small script to change the output from DigiTemp to be even more human friendly

sed -e “s/Sensor 0/Living_Room/” -e “s/#10 : 287B69C7040000BD//”

Then I setup a cron job that runs as root. This job runs every minute and takes the output from digitemp, does the rename, and writes it to a log file. It looks like this in my crontab:
[code language=bash]
* * * * * /usr/bin/digitemp_DS2490 -q -a -c /etc/digitemprc | /home/stevet/bin/digitemp_rename | sort >> /var/log/temperatures

Now let it run for a few minutes and your temperatures log file should begin to add lines of data. It will looks something like:
stevet@neon:~$ tail /var/log/temperatures
2013/07/13 18:08:02 12 Living Room F: 79.14
2013/07/13 18:09:02 12 Living Room F: 79.25
2013/07/13 18:10:02 12 Living Room F: 79.36
2013/07/13 18:11:02 12 Living Room F: 79.47
2013/07/13 18:12:02 12 Living Room F: 79.47

You now are gathering specific sensor data and putting it into a log file to be processed later.

In Part 2, I will add a bunch of sensors to the 1-wire system and show how they all are logged. In Part 3, I will detail how I graphed that data so I can visually see the temperature changes.