Remote Temperature reading for greenhouse

[snappybob]

I had plans to monitor the temperature in my greenhouse with a remote temperatue senser. I have two of them and have used them in the past for simular tasks. I think my greenhouse is blocking the signal. Both of my transmitters refuse to transmit while inside the greenhouse. Here is a pick of my greenhouse.



It's really a big wire cage. I think what I need is a transmitter that has a remote senser so that I can place the transmitter outside and position the thermocouple inside connected by wire. I haven't really even looked to see if something like this is availble but I'll bet it is. I'd also be willing to bet that it's expensive. Both of my sensors are made by Oregan Scientific and have worked semi reliably and semi accuratley. Does anybody else have this problem?

[Fusion_power]

The problem is a low power output from the remote unit and nearly 100% signal blocking by the wire cage. You can somewhat overcome this by attaching the remote near the side between the wires. There is also a distance limitation. My remote has to be within 40 feet of the base unit. I put the remote near the greenhouse wall closest to my house and have the base in a back room of my house closest to the the greenhouse. It can be erratic during thunderstorms, but otherwise has worked for 2 years now.

One caution, you want to measure the air temp in the enclosed area, not the temp next to the plastic cover.

DarJones

[alamo5000]

I think its more to do with the power output than it is the cage. The cage isn't really an issue I don't think.

My thermometer has a 300 foot range. It can easily penetrate metal barns, and a brick wall and a fireplace too sometimes before it recieves at the base unit.

That's from a 200 foot distance.

What you can do is put your meter outside somewhere at the same distance...and then see if there is a reading...if no...then you know its the power, or the wall that the waves must pass through or a combination of both.

The waves that are emitted must pass through several obstacles on their way to the reciever. Each obstacle the 'power' of the signal can be greatly diminished.

Your cage might be acting as an obstacle, the solution is more power I think.

[snappybob]

Thanks, I'll try moving the reciever and transmitter around to see if I can find a combination that works. I don't know how I can add more power. It already has fresh batteries in all units.

[ContainerTed]

Thinking back to my military days, we used a heavily grounded solid copper wire caged room to repair those little emergency transmitter devices. The cage prevented the signal from escaping the shop area and creating a hassle with the control tower.

The cage may have a lot to do with your signal problem, but I also suspect a power deficiency as well. The openings in the wire weave would have to be very nearly the same distance as the wavelength of the frequency used by the transmitter (an example here would be the door of a microwave oven allows you to see into the cooking area, but blocks the microwave from coming out. Anything between the transmitter and the receiver with this kind of weave structure, or anything large made of copper or ferrous methal can drop your signal level.

And, if the radio frequency used by the device is very high, like into the gigahertz range, then anything wet (as in water) can block signals. The microwave range of frequencies are very susceptible to this. That's how microwave ovens heat water - the water catches the energy and converts it to heat. That's why you lose signal on satellite dishes when a huge rain storm comes between you and the satellite. Even leaves on trees can block signal because of the amount of water in the foliage.

I agree with the postings above. Set the transmitter just outside the greenhouse structure and see if you get signal.

Ted
(Who is an old electronics bench tech)

[ireilly]

Ted, you and my dad would have enjoyed discussing electronics. He was an instructor in the Signal Corps in WWII and always ran rings around me in this. Used to tell me how he built his first crystal radio. Had an old tube shortwave that we used to listen to the BBC and such at night (the best time for that).

http://en.wikipedia.org/wiki/Faraday_cage

The attenuation is imperfect here because the ends look exposed but there is some, plus I suspect you have grounded the wire cage in constructing it, so that part would help. But the suggestions are good, just move the transmitter outside the cage and see or the receiver closer and see. Try one at a time to judge the magitude of the effect, plus you will know which structure is impeding it more. Old houses with plaster, lath, and wire mesh especially, tend to block radio waves more than drywall construction. An RF meter would be great but they can be pricey for the home user. Cable techs tend to have them.

The wavelength of AM is measured in miles, FM in feet, so if this transmits on a higher frequency, say microwave like your wireless phones and home networks (802.11-class) it will be shorter still. That means it can pass through smaller apertures but is more easily attenuated for a given power. So it is a case of power and frequency as stated.

Variations of Faraday shields are used to prevent EMPs - ElectroMagnetic Pulses - from reaching modern electronics, especially in MilSpec applications. The old vacuum tubes are not as susceptible to this phenomenon.

[Lee]

Originally Posted by ireilly

The wavelength of AM is measured in miles, FM in feet, so if this transmits on a higher frequency, say microwave like your wireless phones and home networks (802.11-class) it will be shorter still. That means it can pass through smaller apertures but is more easily attenuated for a given power. So it is a case of power and frequency as stated.

Consumer wireless products are designed to operate around
900 MHz, 2.4GHz, or 5GHz. Mine says it's 915MHz. Which
equates to a little less than a foot.

Try making sure you have the transmitter less that a foot from an opening larger than a foot in your "cage" and see if
that helps.

Also, with fresh batteries (hopefully not rechargable) you should be getting the max power for your transmitter. But
make sure your receiver also has fresh alkaline batteries as
well since it will be able to better amplify the incoming signal that way.

An interesting fact told to me by my RF instructor talks about cell phone towers and a similar phenomenon that you are experiencing.
Many cell phones operate at the 2.4GHz spectrum. This equates to a wave length that closely matches the size of a typical oak tree leaf. During the spring, summer and fall months, cell stations have to boost their output power to take into account the additional loss caused by the attenuation of the signal through these leaves. In the winter, the companies save money by reducing the output power without and impact on customer cell performance.
Now, if they'd only pass along those savings!

Lee

[snappybob]

When I got home from work yesterday I moved both of the transmitters from one side of the greenhouse to the other and moved both of the recievers to a wall in a bedroom on the same side of the house as the greenhouse. As of this morning they were both still working. Amazing, this was not a huge decrease in distance. If they are both still working when I get home today, and I have no reason to believe that they won't, I'll move one of them back to it's original position so that I can again read outside ambeint temp again. I'm not sure what frequency they are. I'll check that also tonight.

[Sherry_AK]

I use a relatively inexpensive thermometer w/remote (says "The Weather Channel" on it) with the remote located at least 100' away and it works great. Indoor unit located on west side of house and remote in greenhouse past the east side of the house, so signal goes clear through the house and into the g/h. I use the same one in winter to see how darned cold it is when I roll out of bed in the morning and head out to get the newspaper! (And it's been a pretty low number the past couple weeks.)

Glad you got yours working.

[snappybob]

Sounds like yours works a lot better than mine. Does it have a brand name or a model number on it. I'd really like to get one that keeps a history of the temps that occurd in the last several hours.

[Sherry_AK]

If I recall correctly, this one was advertised to work up to 200'. It keeps only the min/max for past 24 hrs I think (or maybe it's min/max till re-set). I think I got it at either Home Depot or Lowes. Front says "The Weather Channel." Back, in the fine print, says LaCrosse Technology, Model WS-7013U-IT. Freq 915 MHz.

www.lacrossetechnology.com/7013it (also in the fine print ... had to get the ol' reading glasses for this mission!)


There's a nifty little data logger that looks like a flash (thumb) drive which can record temps and then download to a computer. They're a couple hundred bucks though, I think. I did consider getting one just for fun, but haven't done so yet.