433Mhz Wireless Capabilities

sealion99

Hi,

I'm looking at possibly using the 433Mhz RF Transciever for a wireless weather station and would like to know a bit more about the capabilities of the RF device.· I won't be passing that much data, so I don't think the limited data volume issues will be a problem.· I do need this to transmit about 100 ft. from outside to an inside location.· I know that in general the lower 433Mhz frequency should provide a clearer connection that should have better ability to transmit through walls and other obstacles.··Should the Parallax RF module provide reasonable capabilities for this type of use?

Any info on power usage for the module?· My plan is to solar power the outdoor station and store data locally (probably to an SD card)·for transmission when required.· Does anyone have any experience with running the RF module in it's lower power mode and utilizing it's sleep mode?· Just trying to gather some initial ideas before starting prototyping, so if anyone has anything to add please send it along.·

Thanks,
Chris

SRLM

I suspect that the module will do just fine. It has a listed range of 3000 feet, and Parallax appears to have dropped that to 2500'. 100 feet should not be a problem.

As for the power usage, it's given there in the data sheet. IIRC, 10ma for transmit high, and less for transmit low or low power mode. You can use that to directly calculate your power requirements. If even that is not low enough, then you can always use a transistor to turn the module off by toggling the power line to get almost no current.

Chris Savage

Hello,

I think the range information you're looking at may be in error. I will check on this in more detail tomorrow. In the mean time I do have a project under way which uses a solar panel to keep an SLA battery charged for purposes of running a weather-station type system for data-logging. It would not be difficult at all to convert it to transmit the data remotely instead of logging it locally.

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Chris Savage

Parallax Engineering
50 72 6F 6A 65 63 74 20 53 69 74 65
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Brian Carpenter

on the description page ( http://www.parallax.com/Store/Accessories/Communication/tabid/161/CategoryID/36/List/0/Level/a/ProductID/582/Default.aspx?SortField=ProductName,ProductName ) it states that the distance is 250 feet. is that a mistype?

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It's Only A Stupid Question If You Have Not Googled It First!!

Franklin

Yep!

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- Stephen

Chris Savage

Actually I think the 250ft may be more correct.· I need to check the specifications, but the 2500ft may be a rating at full unrestricted power.

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Chris Savage

Parallax Engineering
50 72 6F 6A 65 63 74 20 53 69 74 65


Post Edited (Chris Savage (Parallax)) : 11/2/2009 7:02:13 AM GMT

Chris Savage

Hello,

The error in the documentation is being corrected and the new documentation should be up soon. The 250 foot range is all we rated the module for under the test conditions we have here. The 433 MHz RF Transceiver we manufacture is not set up for full power output. These modules are designed primarily for prototype design and testing. Certification would be required for end-use and testing would be required to determine legal output power. I hope this helps. Take care.

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Chris Savage

Parallax Engineering
50 72 6F 6A 65 63 74 20 53 69 74 65
·

Moskog

I put a 1/4 wavelenght antenna on top of the·almost similar 433MHz transmitter (27980) and then I received signal about one kilometer (3000 ft) away with the RX receiver with the original rubber antenna. That was line-of-sight but this means you could increase the range a lot with replacing with better antennas without changing output power·of the transmitter.

Beau Schwabe

Moskog,

I haven't tried what you are suggesting, but technically by changing the antenna length, you are changing output power of the transmitter. As Chris says ... "The 433 MHz RF Transceiver we manufacture is not set up for full power output. These modules are designed primarily for prototype design and testing." ... So no, the antenna length may not be optimal. 433MHz @ 1/4 wave should be about 43 Millimeters, I measure slightly more than that (about 53 Millimeters including the trace to the IC which would put it at about 350MHz) but it's difficult to tell how far the actual antenna extends inside the plastic covering.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 11/3/2009 8:40:43 AM GMT

Moskog

Well, maybe we Europeans calculate the wavelenght a different way but·I found·the 1/4 wave lenght·to be close to 170 mm.

Here is the quick European way to calculate wavelenght: Take 300 (speed of light) divided by the frequency (in MHz) and you get the wavelenght in Meter. Then divide by 4 to get the 1/4 wavelenght.

300/433 = 0,69 (meter)· ---->· 0,69/4 = 0,173m or 173mm.

Arrest me if I'm wrong!

The antenna I made is similar to the one shown in this web site. The lenght of the radians & the vertical as above.

It is fed by a very short 50 ohm coax cable, (just a few cm) soldered to the transmitter after the rubber antenna is removed. Better with a long cable between the stamp and the transmitter then a long coax up to the antenna. Though the cable from the Stamp is not more then four meters or so. And I had to keep the antenna under the roof because of lightning sensitivity. Works very good and indeed increased the range.



Post Edited (Moskog) : 11/3/2009 4:56:10 PM GMT

Beau Schwabe

Moskog,

Your right... I was taking 173mm and dividing THAT by 4.

So the Antenna's that are on the RF modules we sell are 1/16th wavelength

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Chris Savage

As these RF Modules are for testing, development, etc. It is recommended that the end-user/customer implementing them into a project calculate the necessary LADJ resistor, antenna type and length as well as any shielding that may or may not be needed so that the device will comply with FCC regulations and/or any testing done. While 2500 to 3000 feet may be desireable for an application, the 250 feet we're specifying is nominal power for development and experimentation. In testing these I put a unit on the other side of the building that listened for messages and replied back. Using this scheme I could tell how many packets I was losing as well as how many errors were present for each transmission. They're great for developing applications using this frequency and in most cases you will want implement some error checking into your routines. Take care.

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Chris Savage

Parallax Engineering
50 72 6F 6A 65 63 74 20 53 69 74 65
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SRLM

So would it be possible to hack the modules so that it can output full power? I guess my question is: would the board be able to handle that? Also, would a hacked module be acceptable in the 2010 RF design competition?