Author Topic: DDS 20 Function Generator Kit (Read 33065 times)

MeggerMan · « **on:** July 04, 2007, 01:00:00 PM »

The DDS 20 function generator is available in kit form or assembled from ELV in Germany:
http://shop.elv.de

Kit (without AD811 for sine wave output): 61 EUR
Build (including AD811): 90 EUR

The AD811 op-amp provides a true AC sine wave (+ve and -ve signal). But even without the AD811 you get a full sine wave but it sits above the ground rail (+ve only) and it's amplitude can be controlled by the potentiometer.
Using this signal you can feed to a less expensive external op-amp without voltage follower to give you a variable pulse width output. This can be used to feed a mosfet driver and mosfet for the ECD/TPU project.

Note:When building the kit I have found an issue with the LCD display not displaying all the segments because of the clamping frame tabs do not contact the clear cover.
You need to screw in the screws very carefully and do not over tighten them, just enough to move the frame to touch the board and no more.
ELV sell spare frames I think for this purpose - people over-tighten the frame screws.
Remember you must set the configuration defaults on it before it will start working, press the "Prog" button for more than 2 seconds and just accept all the defaults. I was scratching my head for about an hour before I realised this.

Note: power on the +12V rail is about 90mA rising to 110mA with the outputs loaded and the freq. at 20Mhz.
Power on the -12V rail is about 15mA rising to 23.7mA at 11MHz(peak load frequency) with the AD811 output loaded with a short or capacitor. With such low power requirements lends itself to a low power inductor based inverter using the TPS6735 plus the following:
C1 44uF, C2 10uF, C3 1uF, C4 ~44uF, C5 22uF, D1 1N5817 (schottky 1A 20V), L1 10uH, L2 22uH
The whole board will be about 17mm x 43mm and plug into the two 100uF capacitors pads on the DDS 20 board, one capacitor is transfered to the new board.
http://focus.ti.com/lit/ds/symlink/tps6735.pdf

(http://i100.photobucket.com/albums/m25/kingrs/inverter_schematic_v1-0.jpg)
(http://i100.photobucket.com/albums/m25/kingrs/inverter_layoutv1-0.jpg)

I have included the original German manual and my translation.
I recommend you buy the kit as it is so simple to build and because you still need to add a case and PSU anyway.
I will update this message with a more complete manual when I get more time.

Gregi · « **Reply #1 on:** July 04, 2007, 02:06:20 PM »

Its really great you posted this, cause I'll probably buy it.
Do I need the AD811 for ECD purposes?
Thanks,
Greg

giantkiller · « **Reply #2 on:** July 18, 2007, 05:14:55 PM »

@Meggerman,
I was looking at getting one of these but I remember some noise about the Deutsch site not selling in the U.S. How did you overcome this?
Thanks.
--giantkiller.

MeggerMan · « **Reply #3 on:** July 18, 2007, 05:25:55 PM »

Quote from: giantkiller on July 18, 2007, 05:14:55 PM

I was looking at getting one of these but I remember some noise about the Deutsch site not selling in the U.S. How did you overcome this?

Simply by living in the UK and not the U.S.

I think its the cost of sending the large glossy catalogue (also in German) with your order that may make it too expensive to cross the pond.
What you need is someone in the UK or EU who will post it on to you.
Regards
Rob

Gregi · « **Reply #4 on:** August 11, 2007, 11:57:59 PM »

I received my kit and there is a warning that comes with the manual saying that there is an error in the inscriptions of the board concerning the C24, C27, C34 and C40 capacitors polarity. But as I compare the schematics in the manual and the drawing on the board indicating the polarity, its the same.
So where is the problem? Do I trust the board's and schematics' drawings or do I change polarity as its stated in the warning paper?

Thanks
Greg

MeggerMan · « **Reply #5 on:** August 12, 2007, 01:34:52 AM »

Hi Gregi,
I have both a built board and kits, and yes you are correct, it looks like the warning paper is complete rubbish.
If you look closer at the photo of the top side and the component overlay you will see they are different.
See C24 and C27, they are near the decoupling caps, where in the "real" board layout C27 is next to IC2 and C28.
I only spotted this because I am building an inverter board (+5v to -5V) to solder onto the back side and use the C24 and C27 pads as the connections. I thought, ahh, that's not right.
I think what has happened is that they updated the overlays and component masking on the actual board but forgot to stop sending out the error sheet. I will email Stephanie on Monday to point this out.

Also I found one kit where the pins on the AD9835 were bridged in two places with solder so if you have a microscope (20x or there abouts), just check the pins over. There was one big clod of solder on two pins (easy to see) and a very fine path(impossible to see by eye and tricky even at 20X mag.) of solder balls on the other two pins.
It was like a row of small marbles lined up across your desk where your desk is the 0.3mm gap!
The resistance showed up as about 0.4 ohms across SCLK and SDATA pins.
Shortly, I will post details at the start of this thread, of the inverter board I am designing.

Regards
Rob

Gregi · « **Reply #6 on:** August 12, 2007, 02:09:50 PM »

Thanks MeggerMan.

Now, I looked at the AD9835 chip and I saw some bridging. Could you tell me if it is something normal, or is it a faulty board then?

Greg

Thedane · « **Reply #7 on:** August 12, 2007, 02:55:31 PM »

Gregi:

It isn't normal - so you do have a defective board.

You should be able to fix it by removing the shorts. This can be done with a fine braided solder wick.
Just remove the solder and solder it again (The solder wick usually sucks too much solder off) so the pins looks like the correctly soldered ones

Can anybody confirm that the AD9835/AD9833 chip outputs "noise" when the frequency settings are adjusted?

Gregi · « **Reply #8 on:** August 12, 2007, 04:17:55 PM »

Geez man, its just incredible how in the manual they brag about the numerous tests they made on the board to ensure its quality... and how one need to be careful when soldering not to make bridging.... and there you go... they couldn't be precise themselves. $:-\$

Well, I'll try to correct this thing then.

Thanks,
Greg

Thedane · « **Reply #9 on:** August 12, 2007, 05:05:16 PM »

The board does look like it was done on machines, and sometimes faults happens - this can even happen in large production sizes. $:-\$

Was this board one of their "mount it yourself" kits?
If it was, I would advise that you check all the other solderings visually - as it would seem that their solder paste screen holes either are too big, or the screen itself too thick (This deposits more solder paste on the pads = bridging can occur).

I'm currently working on my own function generator based on the AD9833 chip, but unfortunately programming isn't one of my strong abilities at the moment :'( - but I'm learning

I seem to recall somebody saying that when you change the frequency parameters the generator outputs some digital noise on the output - has anybody seen this? (I tried the search function, but found nothing :'()

MeggerMan · « **Reply #10 on:** August 13, 2007, 09:12:42 AM »

@Gregi,
Your board is fine, do not remove these bridges it is part of the design.
I think TheDane is misled.
So far I have built 6 kits and tested 3 completed boards so I can safetly say I think I know a little bit about it.

Regards
Rob

Gregi · « **Reply #11 on:** August 13, 2007, 12:23:50 PM »

Thanks MeggerMan,

I would've waited for your answer anyways, before doing anything (stupid) with my board.

And Thedane could have mentioned that he never saw these boards before... $:-\$ (though he never said he saw one either)
And just to make sure I've emailed the supplier, so they will surely confirm your answer shortly.

So, many thanks again I'll start soldering soon.

Greg

PS: Oh, and I think I'll need your help with testing the board (if you agree) before I hook it up to the PS. But I'll ask your help when the moment arrives.

MeggerMan · « **Reply #12 on:** August 13, 2007, 09:54:53 PM »

Hi Greg,
You can check it yourself via the diagram on page 6 anyway.
Pins 2 and 3 are joined together and connected to C43.
Pins 10,11,12,13 are connected to GND.

Time to start soldering I think.
Regards
Rob

MeggerMan · « **Reply #13 on:** August 13, 2007, 10:03:00 PM »

Quote from: Thedane on August 12, 2007, 05:05:16 PM

I'm currently working on my own function generator based on the AD9833 chip, but unfortunately programming isn't one of my strong abilities at the moment :'( - but I'm learning
I seem to recall somebody saying that when you change the frequency parameters the generator outputs some digital noise on the output - has anybody seen this? (I tried the search function, but found nothing :'()

@TheDane,
You can look at the noise at various frequencies by refering to the spec sheet for the AD9833.
Its very low level and can be filtered out using some inductors and capacitors.
The output on the scope for the DDS 20 (based on the AD9835) is perfect.
Go for it.
Regards
Rob

Thedane · « **Reply #14 on:** August 13, 2007, 11:01:47 PM »

@MeggerMan

Imho: Shorting out pins should be done on the PCB - not on the pins. They even short the analog and digital grounds together, which in my book then requires a dedicated ground cross-point with a 0 ohm resistor (or small pcb track) between the two grounds - which I can't see they've done.

The noise I'm referring to is switching/sweeping noise - so it's only present when the chip is eg. sweeping frequencies.
(It might be me that misunderstood a post)
I'd be real happy if somebody can make an FFT on a sweeping signal

It would be a shame to miss SM's magic frequencies due to noise in the signal caused by the function generator

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Author Topic: DDS 20 Function Generator Kit (Read 33065 times)

MeggerMan

DDS 20 Function Generator Kit

Gregi

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giantkiller

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MeggerMan

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MeggerMan

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Thedane

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