LabVIEW
Help needed with RS232-bluetooth
Bluetooth and >400m. That sounds VERY strange!
@bogiasac wrote:
Dear all,
I would first like to thank you for taking your time and reading my message.
I am using two rs232-bluetooth dongles to communicate wirelessly with two PCs.
I am trying to send two waveforms from one PC to the other. I am doing this using flatten to string and unflatten from string.
The company states that the rs232-bluetooth dongles are a direct cable replacement.
I am doing this having adapted the Advanced Serial Read-Write example that LV provides.
My problem is that on the receiving PC when unflattening from string i cant find and wire a '1-d array of DBL waveform' to the type of the unflatten vi.
I have used hyperterminal and i know that these dongles work at distances exceeding 400m.
I have also managed to send just one waveform wirelessly but i then sometimes get 'junk' data(either +some huge number or -some huge number). I am using the 'bytes at port vi' and it seems to me that i might have a problem with processing the data in the right way.
I would thus like to know if there is a way to process the 'bytes at port' a few at time.
I am no Labview expert so i would greatly apprecieate any help, preferably in some example vi's or changes on my vi's.
I have read all the knowledge base on rs232 and have looked at a huge number of other peoples questions on rs232 but to no avain.
I am using LV8 and both PCs have reasanoble CPU and RAM memory.
Thanks
Alex
First you should do some protocol. The problem you are running in is that on the receiver side you are just reading how many data there is and then reading it. LabVIEW is very fast so it is likely to read the number of bytes at serial port long before the entire flattened string has arrived so you end up with an incomplete flattened string and the unflatten function will recognize that the data can't be complete and refuses to attempt to unflatten the chunk.
A good solution would be to first send the length of the flattened string by Flattening that number which will result in a 4 byte string. Then send the actual flattened string. On the receiver side wait until you have at least 4 bytes at the serial port, unflatten those 4 bytes to an integer and then read the actual string using this number as the number of bytes to read. If you have very large flattened data and the serial communication baudrate is slow you may first have to wait again until the amount of bytes the flattened string should consist of has (almost) arrived before trying to attempt to read it since the read timeout might kick in before all data has arrived.
Even better would be to read in a loop every 10 seconds or whatever depending on your baudrate, whatever data is present at the serial port appending it to an internal shift register until you have read the amount of bytes you have firstly received. Then take out the indicated amount of bytes putting a possible rest back into the shift register for the next loop to use (if it is already there it would contain at the beginning four bytes being the next size of flattened data to follow) and pass the extracted data now to the Unflatten from string function.
This last apporach if done correctly is indeed a little more complicated but it does make the difference between an application that will work sometimes and one that will work continuesly for long amounts of time. If you need to run this for very long times such as days it would be a good idea to have the receiver send an acknowledgement after each flattened string indicating if everything went smoothly and have the sender only send the next flattened string AFTER an acknowledgement has been received.
Rolf Kalbermatter
Message Edited by rolfk on 04-13-2006 11:29 AM
