Parsing data from serial port into Arrays

[ghostz13]

I've tried changing the range increment, min, max, multiplier with the case statement abv but nothing seems to work... i cannot spread out the high frequnecy waveforms....

[Dennis_Knutson]

ghostz,

You've asked the same question in several threads and on different boards. That is considered 'bad' behavior. Why don't you pick one thread, post your code, and be a little patient in waiting for an answer

[ghostz13]

Hey Eric,

I'm manually setting the X-axis range in the properties instead of using a knob with the property node and it works fine. Problem is when i pass in a 35Hz sine signal it appears like this. Is it possible labview visa or waveform chart cannot deal with the data speed? I require to send signals with frequencies of interest up to 100Hz which is why I'm sampling at a rate of 250Hz.. satisfies the nyquist theorem so the problem shouldnt be aliasing?

Dennis: Sorry abt that. Din know abt that rule.... I tot it was fine to ask a few ppl the question... point noted... I'll stick to this thread from now on...

Regards,

Gerard

Message Edited by ghostz13 on 03-12-2007 10:46 PM

[Rudi_N]

Gerard:

I am still not sure about why you are experiencing such issues plotting your data. 35 Hz is not too high of a frequency for LabVIEW, I am curious to find out how you are sending your data to the plot. Please post your VI so that I can help you further.

Thanks,

Rudi N.

[ghostz13]

Hi Rudi,

I increased my sampling rate up to 2500Hz and the problem still occur. The signal distorts above 10Hz. I'm connecting a function generator to the pin A0 of my pic16f877 (with internal 10 bit ADC) and sending it over by com port to my PC after using a max233 to convert ttl to rs232 voltage levels. The pic converts the voltage level to thousands of millivolts and sends it over in the format XXXX<CR>.

The Vi checks for data in the buffer, seperates the string with <CR> and plots the waveform.

Attached is my VI. Thanks for helping....

Plot

Regards,
Gerard

Message Edited by ghostz13 on 03-14-2007 07:15 AM

[Rudi_N]

Gerard:

 I did not see your VI ...

Rudi N.

[Dennis_Knutson]

Why do you make is so hard? You can attach a file to your post by simply clicking the Browse button right below this message body. Right where it says "Attachment".

[ghostz13]

Din realise there was an attachment upload for the forum itself.. Heres the vi...

[Rudi_N]

Gerard:

Sorry about the late reply. Are you still experiencing this issue? Please let me know.

Thanks,

Rudi N.

[ghostz13]

Hi Rudi,

I've found the problem. Apparantly the microcontroller is not outputting data as fast as i expected hence aliasing problem. So i did a serial interrupt driver on the pic side to reduce the lag and I managed to get a sampling of 200Hz, the min needed (cos i have a low pass filter cutoff 100Hz), the signal can be seen roughly so I'm not gonna touch this project anymore.. Thanks for ya help!

Regards,
Gerard