Looking for Temp and humidity sensors

Isn't the claim here that the one piece sensors, while available, are too expensive?

Actually, you measure the dry and wet temperatures and calculate.

However, when I was an HVAC engineer, when we wanted a serious measure of humidity, we used wet and dry temps. That was years ago, maybe it reflected more pragmatic concerns.

Sure it is, get to temp sensors, put a cotton wick on one into a tank of water. Put a float valve on the tank to control level of water in the tank. Put a muffin fan blowing air across both sensors. Measure and calculate. Periodically backflush the tank to clear out the calcium and other scrud left over from the water. Put in some algecide periodically, etc.

This is, of course, comp.home.automation, so you really need computer sensors for the water temp, flow rate of both water and air, etc.

Too bad. I see other topologies like Phil Anderson's that make me believe the Bobcats could either be made more functional or less expensive, overall, but I suppose for limited uses where the sensor needs to be bulletproof and highly reliable, the Bobcats make sense. With 16 port Ethernet hubs going for less than $50 I would have thought we would have seen more things appearing more quickly for networking like remote temperature sensing and even electrical load control.

And economies of scale never amount to much in small operations like ADI's so the price isn't likely to come down as manufacturing techniques improve. I wonder if HA will ever see a time where component prices drop the way hard drive prices have for PC's? X-10 seems to have come the closest in lowering prices through high volume. It's probably what make it difficult for some people to jump to the next level - almost every other HA control technology is at least double the cost of X-10. That sets up a mental expectation that it will also be twice as good.

It doesn't seem that many people are interested in knowing the temps in each room in the house. I'm probably just a data freak but it seems to me a home automation system HAS to know details like that to effectively conserve energy.

I just want something simple that can log the temperatures and RH's of the various sensors to an ASCII file that I can analyze later. If I had the technosmarts to crack the RF protocol of the RatShack remote thermo/hygrometers (six units, three with RH, three without) and record that output to a text file, I'd be happy. But in reality, I'd like to monitor three temps per room, at least (ceiling, floor and about 3' from the floor. I don't need RH from each room, but I'd like it from critical rooms like the bathrooms, the basement, the pantry, the attic and the kitchen.

Why so many sensors? I believe it will be the foundation of a truly "smart" home that can look for data anomalies and thus detect open windows, clogged furnace filters, improperly operating dampers and a whole host of other things. A house is like a human being in that it tries to maintain a fairly constant internal environment. To do that, you have to have lots of sensory input.

-- Bobby G.

Sure. One could design a more functional Bobcat (e.g. SECU16i + temperature sensors).

ADI's primary business is contract manufacturing of SMT boards for others. If anyone is likely to be efficient, they are. However, Chinese factories can do the same work in small quantities for much less. So, design what you want and send it off to one of them to fabricate.

I designed a small battery powered generic wireless ADC module using a protocol that is understood by the BX24-AHT. It costs less than $10 to make and could retail for about $20 but will cost about $6K for the required FCC ID tests.

The real problem is that *none* of the HA related companies have found much of a market. I recall seeing something from Dan Boone about a year ago before he left ADI that they had shipped 5000 Ocelots.

Anyone with the skills to roll their own can find inexpensive hardware. The JK Microsystems PicoFlash & Pico-I/O can do a lot for about $175.

The $1.60 Insteon PLC chip *might* lead to plug-in sensors of the type you want.

Of course, nobody will be able to walk about without caus>"Dave Houst>

Certainly. But in the design phase some would consider it important to begin taking readings as soon as possible. I'm sure you're aware one of the biggest problems in weather prediction is the lack of accurate and fairly granular data for all but the most recent human epoch. When I get around to considering the CPU of a home automation system, I already want to have a good feel for some of the raw data that will be feeding it.

I've got 6 different places in the house monitored with RatShack remote thermo/hygros, but that data just evaporates with no suitable way to collect it. I'm willing to devote an old PC or laptop to the task of data logging since I can see that doing with with the Elk, Ocelot or HAI boxes is going to be a hack, and probably an unsatisfactory one at that!

Since the system Jeff described would be inexpensive and fairly easy to implement, it doesn't seem like a big risk to me. After all, this is a hobby. If it wasn't this it would be titanium golf clubs or tropical fish. :-) It also had the attraction that the SECU unit was something I intended to acquire for the Ocelot anyway.

measurement

Well, that's certainly an intriguing analysis. I would imagine you'd get a lot of static with a comment like that were it not buried deep in reply like this!

It's apparent one would use the Bobcats for something discrete and important. It's also pretty obvious that Ocelots aren't the best devices to use for critical temperature or humidity readings for a large number of locations. The fact that you can even log and act on temperature/humidity data with an Ocelot (or Elk or HAI box) at all speaks volumes of the "plastic" nature of modern microprocessors.

What do you consider "inadequate?" Is it quantifiable in terms of errors and types of errors? What I am trying to get at is that even if an Ocelot turns on a fan at 78F rather than 80F, does that lack of precision really matter? It may not matter to most end users whether they can measure with + or - 1% or less accuracy.

Again, most HA enthusiasts don't seem to want to retain data, and you correctly point those that do to:

I'm not sure what you mean. Did you take a commercial motion detector and retrofit it to transmit information about three other "states" as well as motion? That sounds fascinating and like an emulation of nature. Take the ear. Great for sound processing AND also provides information about air pressure, gravity, acceleration and body orientation.

provide

An interesting device, indeed. The 1-Wire bus seems to be the way to create an inexpensive but highly accurate sensor net for a house. Are these specs they list for the DS2450 really right?

"Very low power: 2.5µW active, 25µW idle"

-- Bobby G.

Thanks for all the input and discussion, I have been following all of this, and I am very intrigued...

Oddly enough, I read "disruptions" anyway.

-- Bobby G.

Being among the more vociferous "advocates" here, I might have objected... except he's right. :^)

I happen to believe that the home automation controllers I offer are useful and reasonably priced. The ELK M1G, for example, does a credible job of operating various systems and securing access to a home. It is NOT a data logger. It can't collect streaming data and perform actions based on historic information. The same is true of HAI and several other HA-related controllers I sell.

However, for the purposes of most home automators they do a satisfactory job.