USB Serial Communication Continuous

[Dave]

pic-ker, Even if you buy a more expensive rf module pair you will still have the same problem. I speak of a squelch circuit that mutes the data line from the receiver when there is no received carrier. However you will still have to send some kind of sync byte for the program to lock onto for the data stream. Also if you don't send some kind of checksum with the data packet you will have no idea of the data bytes in the packet are valid.

Dave Purola,
N8NTA

[pic-ker]

I am sending a sync packet of '239' in a frame of 6 characters, But I find that there is no need for error checking as I am using this mainly for text messaging..

dave, do you have any kind of squelch circuit in mind ? and how do I detect when the carrier is present ?

[Dave]

pic-ker, There is no easy way to add a squelch circuit unless the receiver you are using has an RSSI output available. This stands for "Reletive Signal Strength Indicator" and it is an output usually derived from the IF portion of the receiver. If this analog signal was to be compared to a reference voltage that signal strength would be the level that the signal has to be to (open or unsquelch or unmute) the the data stream.

Dave Purola,
N8NTA

[mister_e]

Few post before you said you didn't use the RF for now.. is this still true?

If you receive always different things, it sounds like a baudrate problem to me... dpending your config fuses settings, hardware it may ruine your whole life..

try a simple serial comm before adding the USB.

[pic-ker]

Few post before you said you didn't use the RF for now.. is this still true?

If you receive always different things, it sounds like a baudrate problem to me... dpending your config fuses settings, hardware it may ruine your whole life..

try a simple serial comm before adding the USB.

Its true, I tested the TX/RX using a wire initially and there were absolutely no problems with the baudrate or noise etc

Now that I have attached the RF modules I get errors..its probably because this module uses ASK

Ideally the module should not require CRC bits, what I mean is if you send a '1' you should get a '1'

Im trying another data link from here:
www.cappels.org/dproj/LCRFLINK/LCRFLINK.htm

i'll try it and let you guys know...

[skimask]

Its true, I tested the TX/RX using a wire initially and there were absolutely no problems with the baudrate or noise etc
Now that I have attached the RF modules I get errors..its probably because this module uses ASK
Ideally the module should not require CRC bits, what I mean is if you send a '1' you should get a '1'
Im trying another data link from here:
www.cappels.org/dproj/LCRFLINK/LCRFLINK.htm
i'll try it and let you guys know...

Most of those RF modules use ASK. And generally, they don't need CRC bits (that's all up to you), but what they do need is manchester encoding (aka bi-phase encoding) to keep the internal data slicer from losing it's mind.
Search for and check that thread I mentioned earlier and you'll see. Basically, you end up cutting your data rate in half by changing all the 1's to '10' and 0's to '01'. Sounds silly but it works great.

[pic-ker]

Most of those RF modules use ASK. And generally, they don't need CRC bits (that's all up to you), but what they do need is manchester encoding (aka bi-phase encoding) to keep the internal data slicer from losing it's mind.
Search for and check that thread I mentioned earlier and you'll see. Basically, you end up cutting your data rate in half by changing all the 1's to '10' and 0's to '01'. Sounds silly but it works great.

I got my RF module to work...I was using the +VCC from the USB port to power the receiver and that was causing some continuous ripple

I used a battery supply,connected the grounds,used a 0.01uF decoupling cap and now it works..

Thank you guys for your suggestions...
I will post the complete project once the VB.net Code is complete..

[skimask]

I am sending a sync packet of '239' in a frame of 6 characters, But I find that there is no need for error checking as I am using this mainly for text messaging..

dave, do you have any kind of squelch circuit in mind ? and how do I detect when the carrier is present ?

There's a big, long thread (Serin Serout Problem is what I think it's called) that's got loads of good info on how to use some of those cheap RF modules, explanations on the preambles, sync's, etc.etc., why you need them, how many to put out there, etc. Lots of answers for you in there...