Distorted Output; Did I do something wrong?

Distorted Output; Did I do something wrong?

Postby TheWheel » Fri Sep 06, 2013 1:24 pm

Hi Forum,

I received FG085 kit and went straight on building the Function Generator.

There are two problems I now have..

1)
Why is this kit send with a old Firmware (version -110 in stead of -130)!
Can I upgrade the software with a Basic Arduino FTDI board??? Help would be very much appreciated!

2)
The FG085 works like a charm .. more or less.
The main problem is the distortion on the top (SQR) and slopes (All other wave forms, see attached files).

NewFile0: Down slope SINE
NewFile0.jpg
Down slope SINE
NewFile0.jpg (36.03 KiB) Viewed 8185 times

NewFile1: SINE
NewFile1.jpg
SINE wave
NewFile1.jpg (36.35 KiB) Viewed 8185 times

NewFile3: SQR
NewFile3.jpg
Top half of a SQR
NewFile3.jpg (34.53 KiB) Viewed 8185 times

NewFile4: TRI
NewFile4.jpg
TRI
NewFile4.jpg (36.6 KiB) Viewed 8185 times


As you can see there is a BIG distortion on all wave forms. The same distortion I see at the Power Connector (100mV - 250mV spikes!).
I tried an other (better) Power Adapter but that was only marginal better.

The output from the Crystal is clear (no distortion, 20Mhz) and is the only point on the board where I can measure an undistorted signal.
On all the measure point I see the same distortion...

Can anyone please tell me how to fix this.
TheWheel
 
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Re: Distorted Output; Did I do something wrong?

Postby jye1 » Sun Sep 08, 2013 12:45 am

1 ) If the kit was purchased from a distributor he/she might have stocks with older version firmwares. To upgrade firmware programmer is required because there is no bootloader installed due to limited space.

2 ) Usually there are larger noises for signals except sine because the low-pass filter was turned off to keep sharp waveform edges sharp. But from the photos noises were a bit larger than usual. Please check C12 to see if there is a soldering problem. Also please try parallel 100uF caps to C9 and C10 to see if the noise level can be reduced. See schematic at http://www.jyetech.com/Products/085/Schematic_085G.pdf and component location at http://www.jyetech.com/Products/085/Ass ... k_085G.pdf.
jye1
 
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Re: Distorted Output; Did I do something wrong?

Postby omike » Wed Dec 04, 2013 7:53 am

Hi!!! I have a problem this distorsion signal to...

CAM00130.jpg
CAM00130.jpg (627.69 KiB) Viewed 8051 times


[attachment=0]CAM00128.jpg[/attachment

I implemented above-mentioned recommendations... that else it is necessary to look.... firmvare is new..
Attachments
CAM00128.jpg
CAM00128.jpg (645.63 KiB) Viewed 8051 times
omike
 
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Re: Distorted Output; Did I do something wrong?

Postby jye1 » Sat Dec 07, 2013 2:42 pm

The device does contain noises about 50mVpp. For low amplitude output these noises become significant. They are from the digital trimmer. We need hardware change to eliminate these noises.
jye1
 
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Re: Distorted Output; Did I do something wrong?

Postby scruss » Thu Dec 12, 2013 1:12 pm

I was about to post about the same issue; disappointed with the noise level:

Image

I'll check the caps on the board.

cheers,
 Stewart
scruss
 
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Location: Toronto

Re: Distorted Output; Did I do something wrong?

Postby auptown » Thu Oct 23, 2014 3:56 am

Has anyone been able to lower the distortion? I just received an assembled unit from Amazon, works OK, but I am reading > 1% distortion on the sine wave, in the audio band (for example 1000 Hz). When I look with an FFT, I see some noise in th 10kHz - 20kHz range, as well as harmonic distortion, both starting at the base frequency, and also a set of harmonics starting at 250 Hz.

Also looking on a scope, it seems like I see small jumps in the sine wave.

Is this typical for this unit? Or maybe something is wrong?

I see these numbers on startup:

08051-132
08502-050

--Andrew
auptown
 
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Re: Distorted Output; Did I do something wrong?

Postby jye1 » Fri Oct 24, 2014 2:51 am

The noises are typical for this generator. They are from the digital trimmer, which is for amplitude adjustment. And since the sample resolution is only 8-bit and the DAC is a simple R-2R resistor network waveform distortion is also expected.
jye1
 
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