Software timed digital line measurement

[Javed123]

Hardware used NI USB 9215 DAQ

Software used Labview 8.20

I have a vi that accepts input from the above hardware and applies signal conditioning to arrive at a digital signal. Normally the digital signal is low

if no signal is being received. When a signal is received it consists of a preamble start bit data bits D0 through to D8 and finally a parity bit (See attached word doc). I have

managed to detect the preamble by monitoring the rising edges of the preamble bits but am having difficulty in decoding the rest if the data string. (A screenshot

of the vi in operation is shown in the attachment)

Basically I am trying to build a sofware timed digital line measurent vi for this task, any ideas suggestions would help me greatly.

Many thanks

Javed

[JamesC]

Hi Javed,

I am not sure what you want us to do. Are you acquiring this as a AI signal or a DI signal.

Can you record a waveform as it arrives, and also post the code you are using to decode the data bits, then maybe we can look into this.

Also how is the data encoded, is it like RS-232 (Inverted and LSB first)? or is it custom, we would need to know this to work out how to convert your data.

If the input is analog, you could do a comparison on every N number of samples to see if it is above or below a certain value, and this would give you a boolean waveform, so you now have signal level, that can then be converted.

Regards
JamesC
NIUK and Ireland

[Javed123]

Hi James

Many thanks for your reply.

I have managed to get the vi working and its is now decoding correctly the dataword I sent is encoded like RS232 as per detailed in the screenshot in my fitst mail. I have tested the vi out and it always decodes correctly. The only issue I am having at the moment is the performance of the graphing on the vi. After time it seems to miss sections of the graph also the three graphs seem to misalign themselves. (see Screenshot_MissingGraphSection2.doc).

The vi is zipped up into the attachment called emfilter-006.zip

Any help in improving the vi's graphing performane would be greatly appreciated.

Best regards

Javed

[Tom O]

Hi Javed,

I've had a look at your code and have been running it but have been unable to replicate your issue. Is there something you can do to replicate it? It's quite difficult to follow your code so if you could provide me with some more information on the issue, that would be great!

Thanks,