1-wire temperature sensors

[RandyKnight]

So the last thing I need to order for my first round of trimout is temp sensors. I've been investigatin 1-wire, primarily due to the fact that I need more sensors than the M1 supports. Plus the aesthetics of the Elks ones leave much to be desired.

Anyway, I think I need a "1-wire for dummies" link. I've dug through the stuff on HobbyBoards and some other places and I think I know what I need but I'm not sure.

Questions:

Do I need the whole temperature senosr kit with board and everything else or can I just directly wire the DS18S20's to the 1-wire bus? In other words, do I just need a hub (hubs really since I have more than 6 sensors), the serial interface, and the sensors, or do I need the board a well.

If I do need the board, the stuff on hobby boards makes it look like you're back to the aesthetics issue again, no?

 

[DavidL]

You can daisy chain wire all of the 1 wire devices on one wire (hence the name ) and then bring that wire back to the PC and plug into either a serial 1 wire interface or a USB one.

You can also use a "star topology" with the 1 wire hub that hobby boards sells. This is where several "spokes" go out from the hub to your rooms, and then the hub connects back to the PC. I personally haven't used this, but our software developer has and he is saying it works well for him. I have heard other software 1 wire projects have had some difficulty with using the hub in the topology, but that's hearsay and I don't really understand where any difficulty might lie.

 

[Michael McSharry]

There was a recent discussion on mounting the devices here on CC at http://www.cocoontech.com/index.php?showtopic=6742

There is considerably more discussion on the 1-wire subject for HA on the Homeeer Message board.

The need for a 1-wire hub is a function of how you are able to connect the sensors. If you have 6 sensors and they can all be reached by a single cat5 cable without taps into the cable other than the sensor mount then the hub is not needed. If your computer is the middle of the house and wiring starts there and branches in 6 different directions then the hub will be a good idea, but you may be able to get away without it.

When you do connect your sensors it is best to make them as close to directly on the main cat5 cable as possible from an electrical performance perspective. The other consideration is the mechanical strain relief so the electrical connection is not stessed.

When you use a 1-wire hub you are limiting your choices for software that can manage your 1-wire network. xapmcs1wire is a free package that is quite popular. Cinimar, as David mentioned, recently released their version of 1-wire interface software. If you do not use the hub then there are many options from microcontrollers to various sw packages on the PC. I started without the hub and now use two of them in a dual star topology with xapmcs1wire.

 

[RandyKnight]

I get the topology. Star with the hub vs. bus, etc. My main question is what is considered the "device". Just the sensor, or the whole kit?

 

[DavidL]

Each 1 Wire chip can be considered a "device" on the 1 wire LAN. each has it's own serial number programmed into it. This gives the software the ability to track each data update to a particular "device". So, if you have a temp "device" in the master bedroom, then, you can assign an "alias" to that device ID in Cinemar's software. Then, you can speak about the temperature in the "Master Bedroom". and not by "BC0003453334" or whatever it's chip ID is.

I would call the 1 wire adapter, hub, wire(s) and devices the "1Wire Network".

 

[BraveSirRobbin]

HERE is a HomeSeer forums post where I came up with a simple diagram showing the versatile xAP setup using Michael McSharry's software using a one-wire hub FYI.

 

[midon]

Some 1-Wire information is also available on our Documents web page and our FAQ page.

Mitch

 

[dbinaz]

I am still kinda confused on this whole 1 wire thing. Is it 1 cat5 wire? or one single strand in a cat5 or what?

I am very interested in doing this as well, especially since they can be put in water.

 

[Digger]

I think.........

that 1-wire really means one cable. It appears to use several conductors for power and data. I think it makes sort of an addressable loop and each device has its own unique address.

I am waiting "impatiently" (I am not a patient person) to see what ELK comes out with for interfacing with these devices. I think there is a lot of potential for some neat automation and weather related functions with these devices, the ELK, and an automation software package.

 

[dbinaz]

ya, i was reading more in depth. Seems most devices only need 2 wires of a RJ12 cable. So I wonder if you could get 4 devices out of one cat5?

 

[TonyNo]

Here's a resource page by the manufacturer...

http://www.maxim-ic.com/1-Wire.cfm

1-Wire® products provide combinations of memory, mixed signal, and secure authentication functions via a patented single contact serial interface. With both power and communication delivered over the serial protocol, 1-Wire devices are unmatched in their ability to provide key functions to systems where interconnect must be minimized.

Benefits

* Single Contact Sufficient for Control and Operation
* Unique ID Factory-Lasered in Each Device
* Power Derived from Signal Bus ("Parasitically Powered")
* Multidrop Capable: Supports Multiple Devices on Single Line
* Exceptional ESD Performance

 

[DavidL]

digger, you don't have to wait. Several of the software HA packages support 1 wire now. they also support the ELK and act as a hub and bridge across many of these diverse data collection and action systems.

Looking at how much data comes into the Mainlobby Server from many of the 1 wire devices (depends on poll rate), I am suspect on how the ELK will handle archiving significant amounts. We moved from an Access database to SQL Lite due to the load. I can see most of the value of knowing the current temp, voltage, rpm, or other, but historical is also very important for meaningful answers. When you put 20, 30, 100 devices online (which is cheap to do with 1wire), the data gets big, real quick for quality analysis and charting.

dbinez, many of the devices use two wires, the others use three. You can put MANY devices on "one wire" (really, "one cable" that has 2 to 3 conductors). They aren't individually home run wired back to the PC. they are "daisy chained" on the "one wire" back to the PC. You could put 100 temperature sensor chips around the house and connect them all on "one wire" back the PC. The software gets the individual device ID and value and archives that in a database. Once the data is there, you can display the current value, or display a chart of historic values, or do math operations on it for analysis. Whatever.