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
(https://overunityarchives.com/proxy.php?request=http%3A%2F%2Fi100.photobucket.com%2Falbums%2Fm25%2Fkingrs%2Finverter_schematic_v1-0.jpg&hash=f7660e6beb44fe9b507398f10837ab59a2cd4e63)
(https://overunityarchives.com/proxy.php?request=http%3A%2F%2Fi100.photobucket.com%2Falbums%2Fm25%2Fkingrs%2Finverter_layoutv1-0.jpg&hash=c7addd4813ca8e6f8e63e4de8355ad222efe3ee2)
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.
Its really great you posted this, cause I'll probably buy it.
Do I need the AD811 for ECD purposes?
Thanks,
Greg
@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.
Quote from: giantkiller on July 18, 2007, 11:14:55 AM
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
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
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
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
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?
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
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 ;D ;D
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 :'()
@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
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.
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
Quote from: Thedane on August 12, 2007, 11:05:16 AM
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 ;D ;D
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
@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 :P
It would be a shame to miss SM's magic frequencies due to noise in the signal caused by the function generator :(
@Thedane:
Supplier confirmed that those bridges are normal and need to be there.
Here is their response in german:
"anbei erhalten Sie die Bau-und Bedienungsanleitung zum DDS20.
IC 5 ist korrekt beschaltet! Pin 2,3 und Pin 10,11,12,13 sind gebr?ckt."
Greg
Quote from: MeggerMan on August 13, 2007, 04:03:00 PM
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.
Rob,
I have built several DDS generators with AD9833 and AD9834 and they work OK. However, I can still see some noise - mostly oscillator clock 50-80mV super imposed on the generated (sine/triangle) signal.
The passive LPF doesn't do anything to the signal.
The digital output is clear as it bypasses the DAC's output.
Could you take a scope snapshots before and after LPF (let say 10kHz sine) and set vertical resolution at 50mV and horizontal at 5-20ns (smallest possible).
Make sure you turn off channel bandwidth limit function on the scope (if its there) otherwise you won't see the potential noise.
Peter
Dont know the board obviously but tend to think if you could see the bare board you may well see a solid copper block under the said pins. Would save traces on the circuit area. Since you are dealing with frequency, the less to transmit signals across the better to me anyhow. I am in the process of making a three channel gen and I am trying to place things to keep the leads as short as possible.
thaelin
Hi,
I have a question to those who have or know/tested the kit.
I have tested mine and it seems to work good, only one thing since I never had a function gen. before.
When I set it to a frequency, lets say 43kHz, what I see on the scope is that the square output keeps shifting back and forth, sometimes just a little sometimes a half unit of the time base. Frequency is stable, but the whole output shifts as the scope refreshes the screen.
So is this something normal or is there a problem somewhere?
Thanks,
Greg
Hi Gregi,
Are you saying the freq. is changing?
My scope tells me the freq. of the pulse.
Check you are not using the sweep mode (run-----------) between f1 and f2.
Check the trigger level on your scope, if its not set right you will see drift.
On my scope if you use input B it is free running and cannot be set by the trigger.
If none of these work I will check 43KHz on my scope.
Regards
Rob
Exact same item available at www.conrad-direct.co.uk.
If, like me, you don't speak German.
http://www.conrad-direct.co.uk/goto.php?artikel=190316 (http://www.conrad-direct.co.uk/goto.php?artikel=190316)
price ?46.99
No English instructions available so I suspect It is shipped directly from Germany.
So MeggerMans English translation pdf will still be needed. (Thank you MeggerMan :-*)
I hope this is some help
Darren
Hi MeggerMan,
Sorry for the late answer, but I've been on holiday.
So I made a small video about what I see on the scope when any frequency is set.
By the way I am not in sweep mode.
Thanks for looking at it.
Greg