I have a wireless thermometer and it seems to effortlessly communicate with the various sensors I have placed around the house. I would like to be able to have my PC track those readings. It seems like a simple thing to do since thee data is flying around. The problem is how do I capture the transmissions as the fly by? I assume they are using the 433 MHz frequency. While I am somewhat proficient at PC software development, I have never done any hardware work. I wouldn't know where to begin in capturing this data.

I know there are units for sale from various manufacturers but they usually have propriety software for interacting with it. I want to be able to write my own software. "That's my field of expertise, so naturally that's where I want to play."

It seems to me if I can simply poll the device on some schedule, I can easily record the value I retrieve. The question is, "How do I poll the device?" and "How will it answer?"

I have googled this but found very little. Most of what I have found seems to be industrial and scientific. I am more of a hobbyist looking to scratch an itch.

 

The problem is that you have to know a lot about the hardware and any firmware to do this. And it's proprietary. And even if they are willing to share, it's tough sometimes to find the people who actually know anything. It's unlikely they use any standard protocol because there isn't one. It used to be that you could get a setup from Heathkit or others where the idea was that you learned something, but I haven't seen such things lately. You could make your own without much effort, but the cost would be a lot more than the Walmart units. Most consumer goods these days are truly disposable black boxes. The people who designed it may not have even kept records as they probably did it on a one shot contract. Such is globalization. For a while it was a requirement that foreign electronics came with a schematic at least, but they have even given up on that.

That said, you might have a chance if you can look up the chips on a unit and find the detected data stream and hijack it to a serial interface. But even that is non-trivial, but often doable. There is also the possibility of buying or making a receiver for FM (most are FM) on that frequency and recording the bursts for analysis. It's all about how bad you want to do it. It can be done if you want to badly enough, I've done worse. If you know enough about electronics and computing, it's pretty hard to keep you out. It is fairly easy to ensure that it is not worthwhile

Regards
cww

 

Parallax (http://www.parallax.com/) has 433 MHz wireless transceivers, temperator sensors, and microcontrollers. All of this is intended for the hobbyist market. It might be easier to simply use their stuff (or something similar from another supplier) than to try to reverse engineer a commercial black box. Since they are selling the equipment to hobbyists, they provide lots of information on how it works and how to use it. However, it does mean "some assembly required".

I haven't dealt with Parallax, but they have long been well known for their "Basic Stamp" microcontroller products.

 

What's your budget? This stuff here is for industrial use:
http://www.emersonprocess.com/rosemount/smartwireless/

Model 648 is the temperature transmitter having embedded wireless HART. Batteries last several years. No wires. Fit and forget...

Model 1420 is the gateway that provides Modbus/RTU, Modbus/TCP, and OPC output that easily connects to your PC over RS485 or Ethernet respectively. There is even an embedded web server so you can just use a web browser if you like.

Jonas

 

You may want to view Modularm's (http://www.modularm.com/) temperature alarms linked there. We may be able to provide you with a solution based on what you're looking for. Our Datalarm unit can monitor temperature while logging it and our Datahub unit will allow you to display that information through a computer.

 

Thom,
Don't know if you're still pursuing, but I'm with you - having done a breakdown of OS blackbox, they do have a mysterious four hole possible test port on the "home" device that looks promising for a tap to a PC to avoid having to interpret the 433MHz signals assuming we could find a device to retrieve from the ether.

In addition, purchased recently a Weather Station for c $60 that has a blackbox MB with at least four ports on it for potential entry - and the included SW is not very good, so a JAVA or other tool based refit would improve the system dramatically.

email at electrobuff at att.net if you'd like to discuss offline.