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Old 16th February 2010, 03:30 PM   #11
cliffyk is offline cliffyk  United States
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Join Date: Nov 2009
The PCGU1000 can also function as an arbitrary wave generator, in fact quite arbitrary--here is an Etch-A-Wave application I created for a client:

Click the image to open in full size.

Here is the created wave, as reproduced by the PCGU1000:
Click the image to open in full size.

Waveforms can also be captured from other instruments capable of exporting CSV of other usable data files, converted to the PCGU1000 wave library format, and then reproduced at any desired frequency by the PCGU'.

Here's the entire waveform library file for a 10% duty cycle square wave:

Code:
-1.0 (7200)
(0)   
 1.0 (800)
(0)
It does full negative output (0.5 * [pk-pk setting] * -1) for 7200 counts, then do an immediate change (the (0) instruction tells it this) to full positive output for 800 counts.

A five-step staircase would be:
Code:
-1 (1500)
(0)
-0.5 (1500)
(0)
0 (1500)
(0)
0.5 (1500)
(0)
1 (1500)
(0)
If you get one you may like to use the alternate front-end I developed, based in part upon my late departed WaveTek 1288's front panel:
Click the image to open in full size.
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Old 16th February 2010, 09:33 PM   #12
Telstar is offline Telstar  Italy
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Yes, I'm seriously thinking getting the Velleman. Do you know any european dealer?

I have no means (yet) to measure the distortion, besides of the very same pc. My soundcard (infrasonic quartet), though is similar in quality to the rather famous juli@ and both should be several times to anything made by creative.
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"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
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Old 17th February 2010, 08:41 AM   #13
cliffyk is offline cliffyk  United States
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Quote:
Originally Posted by Telstar View Post
Yes, I'm seriously thinking getting the Velleman. Do you know any european dealer?

I have no means (yet) to measure the distortion, besides of the very same pc. My soundcard (infrasonic quartet), though is similar in quality to the rather famous juli@ and both should be several times to anything made by creative.
Velleman's main office and plant is in Belgium...

The problem with square wave generation from a sound card is the low sampling rate. measured in kHz, not mHz (the PCGU1000 uses a 50MHz clock). This also affects sine waves as the wave frequency nears and passes 1/5 the sample rate.

At 192kHz sample rate the very best 10%-90% rise time one could generate would be (1/192k) * 0.8, or 4.1us, which is rather leisurely. A 20kHz sine wave generated at a 192kHz sample rate is defined by 9 samples--this is fine for listening to audio as the human ear cannot hear the distortion but look at a 20kHz wave form a sound card on a 100MHz scope and you will see it's not pretty.

Last edited by cliffyk; 17th February 2010 at 08:44 AM.
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