RF Link question
I see Sparkfun.com has RF link transmitter/receiver pairs for a very reasonable price. Has anyone here used them? They have two frequencies: 318 and 434 MHz. Any idea which one would be better? Both are 4800 baud.
www.sparkfun.com/commerce/categories.php?cPath=16_79
Thanks!
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The more I know, the more I know I don't know.· Is this what they call Wisdom?
www.sparkfun.com/commerce/categories.php?cPath=16_79
Thanks!
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The more I know, the more I know I don't know.· Is this what they call Wisdom?
Comments
anyway, I've used the 434MHz 4800 baud link. it works well, but interference was a serious problem for me. So I wouldn't use it to transmit files or anything like that. I'd try sending some text from one stamp/prop whatever to another one, and send the output to your PC to watch it. If you can send a good amount of text without many junk characters, you should be fine. If you do get a lot of trash though, you might want to consider another wireless solution. But then again, it completely depends on your application.
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The more I know, the more I know I don't know.· Is this what they call Wisdom?
On a differnt RF 434MHz. system, one·that·was designed from scratch,·I am getting 80+ M without an amplifier on the transmitter. This is strong enough to go through several walls to another floor on the opposite end of an office building where I tested it. I thought of the engineers said it was 10 dB?
As far as data integrity - when transmitting by RF you should always add some sort of checksum or CRC calculation to the data. I created some CRC-8 code the other day for my RF system. I need to review it and finalize it and maybe get permission before I share it with the forum. There are some great references to CRC on the web where you can learn to code your own routine by looking at C++ examples. The transmitter would add a CRC to the end of the data being transmitted. The receiver would receive the data, calculate a CRC and then compare it to the CRC it received over RF. If it is the same CRC place the data into a buffer to get used by the rest of the software. If it is a different CRC toss the received data out and notify the main program of a error in reception (if error reporting is important).
I like CRC because of the math behind them.· I don't fully understand the math, but I trust it.· There are other ways to verify data integrity.· You could use a checksum, but there are faults with that.· I suppose a "poor mans" way of varifying a transmission would be transmit a packet x times.· The receiver then needs to receive the exact same packet y times before saying it is good and passing it on to the rest of the program.· Y is slightl smaller than x.· For instance, setup the transmitter to send a packet 10 times.· The receiver needs to receive 8 of the exact same packet before it passes it on.· One could get fancy with the software on the receiving end or simply look for y number of correct receptions in a row.
I hope this helps!
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Timothy D. Swieter
tdswieter.com
One little spark of imagination is all it takes for an idea to explode
Post Edited (Timothy D. Swieter) : 10/22/2007 11:21:09 AM GMT
I guess if people are having OK success with them, then $17 isn't a bad price to pay. I'm just wondering why there are two different frequencies available in the same product, unless it is to enable two-way transmission.
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The more I know, the more I know I don't know.· Is this what they call Wisdom?
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Timothy D. Swieter
tdswieter.com
One little spark of imagination is all it takes for an idea to explode