Build Your Own Wireless Beer Pitcher Monitoring System

Willy K. writes "Technology comes to the rescue when disaster strikes and your pitcher runneth dry. These Cornell students have rigged up beer pitchers that wirelessly advertise to the central serving station when they are empty, prompting alert wait staff to bring another round." Add a few steins and you're all set.

Unlicensed amateur radio operation!

[VT_hawkeye]

As a former ham (still got the license, but haven't done anything with it in years), it's kinda depressing to see that they don't even know what amateur radio [arrl.org] is -- which led them to illegally use the 70-cm UHF band, thinking "amateur" meant "do whatever you want".

They needed a frequency in an unlicensed or research/experimental band.

I see an FCC problem here..

[the_rajah]

From their web page: "The FCC sets aside frequencies between 420 MHz and 450 MHz for Amateur use, thus we are complying with the standard by transmitting our signal at 433MHz." IAHRO (I'm a ham radio operator - for 46 years.) It is fine to transmit on 433 MHz IF they have an FCC license and the transmitter identifies it's call sign at the proper interval. Otherwise, it's not legal.

Amateur radio does not mean unlicensed. Getting a license is very easy. Check with your local ham radio club for details or visit http://www.arrl.org/

Re:Unlicensed amateur radio operation!

[jcwren]

They didn't illegally use 70cm. There is a specific allocation for 433MHz for low power equipment. Radiometrix, and a bunch of others all make perfectly legal transmitters for this allocation.

I believe the 433MHz is secondary or teritiary use. The Europeans equivalent is 419MHz

K4JCW

An alternate solution...

[DrSchlock]

The same problem can also be solved by measuring capacitance of the glass across the remaining fluid. (I don't really understand this, but I'm believe it's fairly simple.)

The article references this, in fact.

http://www.merl.com/projects/iGlassware [merl.com]

Re:How is this so different?

[DrSchlock]

It's a different way of solving the same problem, and a reasonably clever one at that. Each idea has its points; the original capacitance method is cheaper, as the authors observe, but it also doesn't work well with viscous fluids that cling to the side of a container and conduct electricity around its circumference.

No FCC problem

[Dr. Mu]

Though I'm no regulatory expert in the matter, I've seen numerous unlicensed devices operating at 433 MHz. As long as they adhere to Part 15 [gpo.gov] of the FCC rules, they're likely okay.

Re:No FCC problem

[n6mod]

There is in fact a section of part 15 (don't remember it now, sorry) that permits very, very low power transmission on VHF and UHF frequencies. Garage Door openers and the like. 433MHz has become popular for weather stations and similar devices.

73 de N6MOD

Plagiarisim

[stendec]

Funny how your post is so familiar [slashdot.org].

Re:I see an FCC problem here..

[djplurvert]

First of all, I too am a ham and hold a "new" extra ticket in case anyone cares.

Many hams seem to not understand Part 15 [arrl.org] which allows unlicensed operation in almost ANY part of the spectrum. In particular, there are only a very few specific frequency ranges where "intentional radiation" governed by part 15 is not allowed. This simply means that you are building a device which is intended to be a transmitter as opposed to being one accidentally. Computers, for example, transmit accidentally and are therefore goverened by part 15.

There are also specific ranges, such as those used by wireless phones and 802.11b, where there are bands set aside with specific restrictions on power, antenna size, etc.

Even if there is no such range in the 430mhz band one can still use that band as long as you restrict the field strength of your transmitter to 200 microvolts/meter measured at a distance of three meters from the antenna. From a practical perspective this is a transmitter that if placed inside a small building probably would not radiate significantly beyond the walls of the building.

Part 15 transmission should not intefere with licensed transmissions and hams are very protective of their hard won spectrum space. Thus hams seem to frequenly speak out against unlicensed usage even when it might not be warrented as they have experienced significant inteference and spectrum space loss over the years. While it doesn't necessarily sound like this is inappropriate use of 430mhz, whenever you are operating close to ham bands it would behove you to be sure you are operating within the bounds of the law. Not becuase "it's the law", but because hams are very protective and self-policing and you are more likely to get a complaint than if you are in one of the specific part-15 ranges.

On the other hand, the comments on here that suggest it's no big deal to cause interference seem to reflect the general ignorance of slashdot in regards to radio/electronics. Before you start talking about "leaky transmitters" sic, and rules you have never read, perhaps you should go read a book or two on the subject.

/plurvert