RF transmission question ...

enfox

I have a question concerning rf transmission. I am writing code to send text from one stamp to another via a transmiiter and reciever. I am able to send characters but sometimes one of the cahracters does not transmit. Say I type "hello", sometimes I get "hllo" on the other end, the character that does not recieve varies from time to time. With RF am I able to use the fpin to control the rate so that all data is recieves? Or is this even my problem?

I am able to see what is being sent and recieved by sending the characters to LCDs on both ends. I am also using a baudrate of 1200 and I wait for a specific character before recieving one so I can filter our garbage.

LoopyByteloose

Controlling the rate may help, but you really need a better software solution.

Last year, Nuts & Volts had a article tht explained Cyclical Reducdancy Checks. You may want to read it.

Rf is prone to interferance from the atmosphere that will occasionally cause distortions and dropout. So the best solution is one that routinely checks and immediately re-transmits data if it is not correct. This is a Cyclical Redundancy Check [noparse][[/noparse]CRC].

You may look and look forever for the problem and not find a 'hardwire' solution. Meanwhile the CRC software will give you 100%, but at a bit slower transmission rate to allow for the checking process and re-transmissions.

Get your CRC software operating correctly at a slower rate and then you may be able to move the transmission speed up to the limit so as to not notice a slow down.

Of course, lightning and sun spots will still slow transmission down. Also, if you are out of range or in a concrete elevator shaft, you will have trouble. Generally, any environment that is difficult for a cellular phone to opperate is somewhat limited in reception unless both the transmiter and reciever are directly in line of sight of each other.

I imagine the high voltage from flourecent lights may be a bit of a problem too. You might select a baud rate that does not easily divide by 60 as you may be getting a harmonic RF interferance from the 60 cycle AC in the high voltage transformer.

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G. Herzog in Taiwan

enfox

hmm, this the only way I can achieve this? I am sure transmitter side is working, its teh reciever side that has problems. CRC seems rather complicated, this is why I ask. Thanks for the help thus far.

knightofoldcode

I have to agree that CRC is a hard thing to implment, however it will give the best results.

However. I don't think that this is your problem, or your solution. I suspect the problem is not based on the RF transmission but on the recieving of the data. IE, I think you'd have the same problem even if you were using a hard wired connection. If this is correct, then utilizing the flow control pins would give the desired results.

Basically, you need to find out if it's only on the RF link. If it is, then the problem will require some form of a CRC.
If it's not working when hardwired and the same symptoms as the RF link, then it's likly to be a software timing issue. In this case a Flow Control would be the best option.

Also, what RF set are you using? There are several that Parallax offers and several that competitor's offer.

Knight.

Tom Walker

Also, keep in mind that any error checking scheme, CRC or otherwise, will, by definition, require two-way communication. A single transmitter and receiver will not suffice. Transceivers on both ends will work.

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Truly Understand the Fundamentals and the Path will be so much easier...

knightofoldcode

Tom Walker said...
Also, keep in mind that any error checking scheme, CRC or otherwise, will, by definition, require two-way communication. A single transmitter and receiver will not suffice. Transceivers on both ends will work.

I hadn't even thought of that fact! I just assumed it was a set of transceivers.