Electronics > Beginners
how arbitray waveforms are generated
<< < (6/8) > >>
nfmax:

--- Quote from: james_s on November 24, 2019, 04:36:22 am ---AWGs produce periodic signals, at least the few I've played with did. The shape of a cycle is arbitrary but the cycle plays repeatedly as the selected frequency. I don't actually know what people typically use them for, other than playing around I never found a need for anything other than the usual sine, square and triangle waves.

--- End quote ---
Not necessarily. You can run in 'triggered burst' mode where an external pulse causes the waveform to play, either just once or for a programmed number of repeats. Recently, I have been using this to play shaped tone bursts, designed using Matlab to have a specified bandwidth, duration, and autocorrelation function, into an ultrasonic transducer. This is what ARBs really shine at.

The waveforms are only a few hundred points long. I'm using an Agilent 33522B which lets you set the waveform sample rate to whatever you want (50 Msps in my case) while interpolating up the actual, fixed DAC sample rate of 250 Msps using a digital filter in the internal FPGA.
rstofer:
At some point, generating the waveform is like a side issue to all of the surrounding features.  A true AWG can do a lot of really neat things.
On the low end, I built a Halloween animation that was simply a skeleton rocking in a chair while snoring.  The sound effect was derived from a .wav file that I ripped from somewhere and played by a PIC with an R-2R DAC.  It worked really well.  It's been a long time, I don't remember how I got from .wav to discrete samples but it was easy, whatever is was.
james_s:
A .wav file is nothing more than discrete samples with a header so it's not hard to do.
joeqsmith:

--- Quote from: rstofer on November 23, 2019, 06:18:02 pm ---
--- Quote from: joeqsmith on November 23, 2019, 05:58:22 pm ---
Fun times.   I constructed an engine simulator and needed to have different waveforms for the various sensors.  I wanted to be able to control the frequency as well as AM and FM modulate so I used an FPGA to do everything.

--- End quote ---

I like analog computing and simulating the suspension of a vehicle (at least one front tire) is a classic problem since it is essentially a mass-spring-damper problem and those are well understood.  But what if the ground under the tire contains a chuck-hole?  I have toyed with the idea of using an AWG to generate the surface.  I could do this quite easily with the Analog Discovery 2.  I could even model those nefarious speed bumps!

Other than sheer laziness, I don't know why I haven't done it yet.

AWGs could be a lot of fun to play with but I'm just guessing that the frequency is going to be a whole lot less than 400 MHz.  For my suspension project, even the 12 MHz bandwidth of the Analog Discover 2 is FAR more than required.  Nothing on the chassis is working in microsecond time scales.  If it does, I guess we move to Euler's Method.

--- End quote ---

I need sub 1 MHz for the simulator.   I will collect data off the real setup and feed that into the simulator.   It was a fun and useful project.  Video showing the basics.   
https://youtu.be/q_89qoFMivg?list=PLZSS2ajxhiQBvWvqMVLdRQMjGofKpQUJr&t=2202 


--- Quote from: rstofer on November 24, 2019, 04:25:14 pm ---It's common to think about repetitive waveforms but that doesn't have to be the case for an 'arbitrary' waveform.  The waveform will repeat but the experiment may be over before it does.

--- End quote ---

True.  Running a test right now doing just that.   
rstofer:

--- Quote from: james_s on November 24, 2019, 06:14:40 pm ---A .wav file is nothing more than discrete samples with a header so it's not hard to do.

--- End quote ---

Something along the lines of 'dump the header' and 'keep the samples'.  It's been about 15 years and I'm getting old...
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod