1-Wire Sensor Network

[willnue]

If you interested in utilizing the Maxim 1-Wire sensors with your Arduino and are looking for a convenient way to connect everything together, check out my Easy Arduino 1-Wire Sensor Network article. It shows how to use some off the shelf phone components to build a nice 1-Wire system.

I am currently using the 1-Wire sensor network to track temperatures at various locations around my home. You can see the temperatures in real time here:
http://nuewire.com/things/

Article on how to build it:
http://nuewire.com/2011/04/easy-arduino-1-wire-sensor-network/

willnue

[robtillaart]

Looks very good - almost professional -  indeed!
well done

[willnue]

robtillaart,

Thanks for the positive feedback. It's been running well since I deployed it a month or so ago with about 200 feet total length of cabling between the nodes.

I'm working on adding building a new outdoor node that will read temp, humidity and ambient light.

willnue

[robtillaart]

@willnue
What sensors do you use for humidity & light?

Rob

I had the idea to let an Arduino act as a 1-wire device to make it possible to add any sensor to 1-Wire. What do you think of that?
For the moment it is on my - too many ideas, too little time in one life - list.

[willnue]

I'm using the DS2438 1-Wire smart battery monitor from Maxim as the base for the node. It has a built in temperature sensor similar to the DS18B20 and an analog to digital converter (VAD pin) that can read the voltage of whatever you connect to it. It also has the ability to read the voltage on it's VDD power supply pin.

For the humidity sensor I am using the Honeywell HIH-4030 analog sensor on a breakout board from sparkfun that I connect to the VAD pin of the DS2438 to read the voltage and then convert it to humidity.

For the light sensor I am using a simple photocell that I will insert in between the power supply and the DS2438 on the VDD pin. I still need to workout the right configuration to feed the right range of voltage to the DS2438 so it can still function. As the light increases and decreases it will change the voltage accordingly  being supplied to the DS2438, which I can then read and map to a scale for ambient light.

I have the DS2438 and humidity sensor working fine, just need to finish the photocell part. Got sidetracked on trying to come up with some kind of outdoor enclosure for it.

DS2438 info at Maxim:
http://www.maxim-ic.com/datasheet/index.mvp/id/2919

willnue

[pwillard]

Nice project!

So how does Thingspeak differ from Pachube?

[willnue]

ThingSpeak and Pachube are very similar, but at the moment ThingSpeak is free including historical storage! ThingSpeak is newer and smaller, but seems to be implementing new features pretty regularly. The are also very responsive to problems as well as feedback.

willnue

[tkbyd]

If I understand what the OP has done... it "shouldn't" work!

I am delighted for him that it does! And of course just because it "shouldn't" doesn't mean that it won't, but 1-Wire networks "don't like" star topologies... which is, I think, what he's done.

The longer the "arms" of the "star", the more likely problems are.

Try to daisychain 1-Wire devices, if they are all on one channel.

[willnue]

If I understand what the OP has done... it "shouldn't" work!

Don't confuse shouldn't work with not optimal. Per the Guidelines for Reliable Long Line 1-Wire® Networks at Dallas http://www.maxim-ic.com/app-notes/index.mvp/id/148 the star topology is listed as a 1-Wire network topology...

Star topology: The 1-Wire bus is split at or near the master end and extends in multiple branches of varying lengths. There are slave devices along, or at the ends of, the branches. ... When different topologies are intermixed, it becomes much more difficult to determine the effective limitations for the network. As a rule, the designer should apply the most conservative of the criteria in these cases.

Note, the document does go on to caveat star topologies...

Precautions with Star Topologies
Testing has shown that unswitched star-type network topologies (i.e., those with several branches diverging at the master) are the most difficult to make reliable. The junction of various branches presents highly mismatched impedances; reflections from the end of one branch can travel distances equal to nearly the weight of the network (rather than the radius) and cause data errors. For this reason, the unswitched star topology is not recommended, and no guarantees can be made about its performance.

For my application I was less concerned with "guaranteed performance" from Dallas and more concerned with simplicity in building and deploying. My network currently consists of about 200 feet of cable split between 5 nodes on a star topology and has been working fine for months.

If you are looking at deploying a network with many devices over 100 meters or more then you probably want to stick to a linear or stubbed topology...

willnue

[JChristensen]

Nice job indeed!  I've used Pachube but wasn't aware of ThingSpeak, will be checking it out.  How does the data get from the Arduino to ThingSpeak?

[willnue]

There is a thread in the Home Automation and Networked Objects forum already that talks about the options:

ThingSpeak Client to Connect Arduino to the Internet
http://arduino.cc/forum/index.php/topic,52331.0.html

It seems that the majority of people go with an Ethernet shield and post directly from the Arduino, but I preferred to connect it to a PC so I could log it locally as well as send it to ThingSpeak. To do this I wrote a small windows application that listens to the serial port and then sends it. You can see my post in the thread I linked to above or skip directly to it at http://nuewire.com/seriot/

willnue