Building a custom 2 adjustable generators and frequency meter circuit.

Using Arduino Project Guidance
1

Hello.

I want to build a circuit that will use Arduino and two AD9850 or AD9851 modules - I don't understand the difference between them, besides operating frequency.

I want to have a knob to move two signals from two modules out of phase with each other.
Also I want to have two knobs that will tell each module to produce a different frequency so I can dial it in within range.
A keypad will be used for a wider range of frequency settings, I suppose.

I want to use coder knobs as input devices with my Arduino and use an LCD for output.

I also want to include a frequency meter. Either a separate IC such as ICM 7226B or a microcontroller itself.

  1. For a range of up to 100MHZ, what Arduino module should I use to have the right number of pins and processing power for the job? (AD985-X do all the work by themselves)

  2. How should I build amplifiers to amplify the signal from generators over a wide range of frequencies?

  3. Should I use a separate frequency meter IC or use the resources of this Arduino module?

  4. Should I shield the meter side from the generators?

  5. Did anybody build anything similar before?

Thank you.
--Vladimir.

2

I want to build a circuit that will use Arduino and two AD9850 or AD9851 modules - I don't understand the difference between them, besides operating frequency.

  1. For a range of up to 100MHZ, what Arduino module should I use to have the right number of pins and processing power for the job? (AD985-X do all the work by themselves)

To answer this we need the datasheets...
Please post a link.

3

Datasheets:

Frequency Meter:
http://www.intersil.com/content/dam/Intersil/documents/icm7/icm7226a-b.pdf

DDS generators:
http://www.analog.com/static/imported-files/data_sheets/AD9850.pdf
or
http://www.analog.com/static/imported-files/data_sheets/AD9851.pdf

Please suggest me if there is something better to use than the ICs and modules that I had listed above.
I am not sure if I need a separate IC for a frequency meter or if I should use Arduino itself.

http://www.jianpingusa.com/serFCmodule.asp - but this goes only up to 50 KHz.
Is there a better IC that I can use so it has the same frequency range as DDS?

What OPERATIONAL AMPLIFIERS should I use on the output of DDS or is there one on generic AD9850 -AD9851 modules?
Thank you.

4

Lots of relevant material on Internet:
http://lmgtfy.com/?q=AD9850+AD9851+arduino

Ray

5

mrburnette:
Lots of relevant material on Internet:
http://lmgtfy.com/?q=AD9850+AD9851+arduino

Ray

I was asking for personal experience, not for what I can Google myself. Maybe someone had built something similar.

6

I was asking for personal experience, not for what I can Google myself. Maybe someone had built something similar.

On the first page rendered by my query, you would have found this topic: Using the Analog Devices AD9850 DDS with an Arduino board
Also, you would have read the layman's explation of the difference between the AD9850 & AD9851.
Also, you would have found Arduino code for initializing the AD985x.
Also, you would have discovered the mathematical equation for setting the output frequency...
Also, you would have read the C++ code equivalent to the frequency equation.
Also, you would have the full demo code for:

An example project that just initialises the DDS and sets the output frequency to 10 MHz can be downloaded here.

And all from the 1st article.

Your graphic was most likely meant to be a smart-ass response to my simple reply. But a considerable amount of my time went into getting you a composite query that would provide quality output. However, maybe some other member(s) will chew and regurgitate information in a fashion you are able to assimilate.

Ray

7

mrburnette - you are not being helpful and you are rude. Please stop replying to my forum post.

This looks very similar to what I want to build:

  1. I read several articles that explain the difference between ad9850 and ad9851.
    I cannot understand the difference still. They seem to always be listed as alternatives.

  2. Based on: http://www.elechouse.com/elechouse/images/product/AD985x%20DDS%20Module/ad9850_1%20manual.pdf

In ad9850 and ad9851, does Square output 1 and Square output 2 give out the same wave from, Square output 2 the wave is reflected along the Y axis? 2 sine and 2 square wave outputs for one generator IC. Why?

I need some way to predict the amount of pins that I will use in my project.
An oscilloscope function may be incorporated.
What Arduino module should I purchase?

4)Should I use ad985X in serial or in parallel communication mode? Serial uses less pins.

Thank you.

8

Why would you want a frequency counter?
You're telling the devices what frequency you want - just put that on a display.

9

AWOL:
Why would you want a frequency counter?
You're telling the devices what frequency you want - just put that on a display.

I am building a research jig. I want to be able to measure resonant self-frequency of what I am going to test.
Is there a good frequency meter IC that I can use that will count frequency and send it to the Arduino or should I use resources of Arduino itself? What Arduino shall I purchase? Thanks.

PS I realized that phase shift between the generator and the input of the measuring side of the circuit is also important if it can be done realistically.

10

Since I will likely be rude in ways similar to mrburnette, I'll keep my thoughts to myself.

11

I googled what I could think of, I read some datasheets, but I have no experience working with DDS and similar things.
I don't know the terminology.
I am new to this.

Why do we have two outputs that are sometimes called "Complementary Outputs" on AD985x ?
Two outputs with 180 degree shift, both for square and sine?

How do I know what microcontroller to use so it has the right number of pins for the task?
There were times when I bought a microcontroller and the number of pins was too small for my project.

http://lgrws01.grayhill.com/web1/images/ProductImages/Opt_Encoder_62P.pdf
Would this work as an encoder? (I want an optical encoder for this task. It will be rotated a lot.)

Do they make DSS with amplifiers? I found nothing for sale in the $5 - $40 price range.
What is GBW in relationship to an op amp? (Simple amplifier for AD9850 DDS? - Page 1)

Any amplifier you would recommend for this task from your experience?

=======================
When I Google for solutions I find the most well-advertized solution, such as an IC.
Not always the best IC or a module to use. This is why I am asking all those things.

Thanks.

12

Start at the end.

Not always the best IC or a module to use. This is why I am asking all those things.

Note that the word "best" is ambiguous at best. :slight_smile:

Not the best might be good enough to meet your requirements. AD985x is a solution not a requirement (most of the time)

So when starting a project you should get your requirements complete, unambiguous, verifiable, quantified etc. Writing requirements is a craft to be learned partial the hard way. imho - http://www.volere.co.uk/index.htm - is a very useful requirements method

Some answers to best (there is the B word again) of my knowledge
1)
Many applications need them and it is fairly easy to generate I guess.

top down: make a design based upon your detailed requirements. Your design should meet all "user stories" or scenario's describes in your requirements.
bottom up: start with a MEGA and build the project and do the counting afterwards. Then you can scale down to an appropriate processor.
Processors that do not fit in today's project might work in your next,

Would this work as an encoder? (I want an optical encoder for this task. It will be rotated a lot.)

  1. Here again the details of requirements is missing. quantify" a lot". The datasheet states "• Reliable, Up to 2 Million Cycles", For some projects that is a lot , for others a few, for yours .... There are non mechanical ways that have a much higher life expectancy.

  2. don't know.

Any amplifier you would recommend for this task from your experience?

  1. don't know

Hope this helps.

13

Thank you.

Why does AD985x have several outputs if it has only one generator?

14

In some circuits, it is necessary to have an inverted version of the output. But if you simply invert one output by using an external inverter, it will have some amount of delay, making the two signals no longer exactly 180 degrees out of phase. Since the time of the delay is constant, the phase delay will vary with frequency.

GBW is Gain BandWidth Product. Product because it is the multiple of the frequency and the open loop gain at that frequency. It is the frequency at which the open loop gain (no negative feedback) of an Op Amp is equal to one. This also can tell you the maximum open loop gain at a given frequency. If the GBW of an Op Amp is 40MHz, then at 20MHz, the open loop gain is 2, or at 40MHz, the open loop gain is 1.

It is more useful in telling you the bandwidth with a given gain, done by negative feedback. Here is how it is used if, for instance, you need a gain of 10. So you calculate your resistors to get a gain of 10. If you need a bandwidth up to 4MHz, then 4MHz x 10 = 40MHz GBW. It works the same whether you are using it as an inverting or noninverting amplifier.

Note that this doesn't mean that you get flat gain out to 4MHz. It means that the gain drops to -3dB (about 70% of the original voltage gain) at 4MHz, and continues to drop at -20dB per decade. You can see why you'd need Op Amps with very high numbers for even modest frequencies, if you need higher gains. A high speed Op Amp circuit is subject to things like parasitic capacitance and inductance, so the higher you get, the more careful you must be to avoid those things that would change the gain with frequency.

Sometimes you just need a buffer amplifier. In that case, the bandwidth and GBW are the same, since the gain is 1 (or -1).

Here is an excerpt from the 2nd edition of Op Amps for Everyone, just covering parameters. If you think that is complicated, wait 'til you read the whole book.
http://www.ti.com/lit/ml/sloa083/sloa083.pdf

The whole book is available online, 2nd edition. The 3rd and 4th editions are not free and are print editions.
http://www.ti.com/lit/an/slod006b/slod006b.pdf

It is a good idea to do just as you are doing, see if anyone else has already designed this or parts useful to you, and use their work as a guideline or just copy parts of it.

Now if someone is going to say that this was somehow rude or grumpy, I want you to quote the parts you think are such. Complete sentences, not edited. This last paragraph excepted.

15

In some circuits, it is necessary to have an inverted version of the output. But if you simply invert one output by using an external inverter, it will have some amount of delay, making the two signals no longer exactly 180 degrees out of phase. Since the time of the delay is constant, the phase delay will vary with frequency.

So 2 outputs are always 180 degrees off one another or can this be adjusted?

Datasheet: http://www.analog.com/static/imported-files/data_sheets/AD9850.pdf
Datasheet Quote:" The device also provides five bits of
digitally controlled phase modulation, which enables phase
shifting of its output in increments of 180°, 90°, 45°, 22.5°,
11.25°, and any combination thereof "
Phase shifts in relationship to the instant I started the generator or between output 1 and output 2?

Does this IC offer a way for me to trigger the oscillator to start at a specific time so I can trigger two AD9850s with a single microcontroller command impulse?

GBW is Gain BandWidth Product. Product because it is the multiple of the frequency and the open loop gain at that frequency. It is the frequency at which the open loop gain (no negative feedback) of an Op Amp is equal to one. This also can tell you the maximum open loop gain at a given frequency. If the GBW of an Op Amp is 40MHz, then at 20MHz, the open loop gain is 2, or at 40MHz, the open loop gain is 1.

I read everything I found about GBW on the internet. You could have just told me that it stands for Gain BandWidth Product.
The rest I could find.

It is more useful in telling you the bandwidth with a given gain, done by negative feedback. Here is how it is used if, for instance, you need a gain of 10. So you calculate your resistors to get a gain of 10. If you need a bandwidth up to 4MHz, then 4MHz x 10 = 40MHz GBW. It works the same whether you are using it as an inverting or noninverting amplifier.

The whole book is available online, 2nd edition. The 3rd and 4th editions are not free and are print editions.
http://www.ti.com/lit/an/slod006b/slod006b.pdf

It is a good idea to do just as you are doing, see if anyone else has already designed this or parts useful to you, and use their work as a guideline or just copy parts of it.

Thanks.
I will check out this book, however I see no point in developing my own amplifier. I will never become an expert so all I am looking for is the existing solution that fits.

LT1253
http://www.k8iqy.com/miscellaneous/18dblt1253ddsamplifier/lt1253ddsamp.htm
http://cds.linear.com/docs/en/datasheet/lt1253.pdf

LM7171

However, my expectations for the amplifier are:
I want to use the device I am building to test transformers so realistically, I will need an amplifier that functions below 1mHz along with some powerful full - bridge circuit to amplify the output. and drive the appropriate winding.

I may use this device for other applications, such as resonance tests of RCL circuit self-frequencies and frequency measurements by frequency matching, strobe for my oscilloscope, etc.

So I may use another amplifier for this perhaps, or use a generic amplifier without the MOSFET bridge.
This (mentioned before) lt1253ddsamp
if almost exactly what I need but I don't want to make it.

THANK YOU

16

From what I can tell from the datasheet and the block diagram, the phase shift is relative to when it started. The output and complementary output remain 180 degrees out of phase with each other. So if you wanted two sine waves with a variable phase to each other, you could synchronize two AD9850 and alter the phase of one of them.

Here is some information on that:
http://www.analog.com/static/imported-files/application_notes/599711852800924681833359689AN-587.pdf

I don't know enough about that chip to tell you if you can tell it the phase shift and have it start up that way. I suspect you can, it should be there somewhere. Hopefully, someone here has direct experience with it. Page 3 of the PDF above seems to indicate that this is indeed possible.

BTW, I'd read an article just a few days ago about stabilizing the output over frequency. See, you put a lowpass filter on the output so the steps from the DAC don't come through, but the signal then drops off gradually up to the cutoff frequency. I went and found the article again.

Warning: Rant follows

I read everything I found about GBW on the internet. You could have just told me that it stands for Gain BandWidth Product.
The rest I could find.

Well, I can't please everyone. I just had several people jump down my throat for not writing a book in my answer.

I don't get why people are so picky about exactly precisely how the answer is worded. The help is free, show some gratitude.

That was not entirely directed at you, I appreciate the thank you at the end of your message, and you've said nothing to me to warrant me jumping on you.

I'm just recalling how you jumped down mrburnette's throat here, calling him rude because you didn't like how he worded his attempt at helping you with the information given. I'm also stinging from the words of several other newbies (and not so newbies) calling my admittedly often terse responses rude or snarky, and calling me Mr Grumpy because I don't stroke egos.

It helps if you tell people what research you have done, or at least mention that you have done some searching and didn't find satisfactory answers. Sadly, there are a fair number of people who come here who have not done any real research, and want it all handed to them.

Some who've been around here for a very long time tend to get right to the point. You may experience Grumpy_Mike at some point. If you get angry at how he answers questions, it will be your great loss.

Keep in mind that we don't know you. We don't know how much you know, or exactly what information you are looking for. We don't know what kind of day you've had, nor do you know what kind of day anyone else here has had.

17

What is the lowest frequency that AD9851 can output? Is it 1 Hz?

I am still in search of an amplifier circuit for my project.
Most likely I will use my circuit at around 10KHz to 1MHz.

How would I remove a crystal oscillator from this circuit?
http://www.aliexpress.com/item/AD9851-DDS-Signal-Generator-Module-2-Sin-Wave-0-70MHz-and-2-Square-Wave-0-1MHz/587051193.html

Is it worth trying?

Arduino runs off it's own clock source and doesn't have to be in synch with 2 DSS modules?

18

VT91:
What is the lowest frequency that AD9851 can output? Is it 1 Hz?

No, much lower - the lowest frequency depends on the clock frequency (and the resolution of the phase accumulator)

How would I remove a crystal oscillator from this circuit?
http://www.aliexpress.com/item/AD9851-DDS-Signal-Generator-Module-2-Sin-Wave-0-70MHz-and-2-Square-Wave-0-1MHz/587051193.html

Soldering iron and solder wick.

Arduino runs off it's own clock source and doesn't have to be in synch with 2 DSS modules?

Correct.

19

AD9850 or AD9851 outputs a sine wave. To convert it to square wave a comparator is used. Am I correct?

It makes no sense because sine wave is modulated out of little rectangles only to be converted back into a rectangle.

Should I look for a different DDS IC? I want to generate narrow impulses, not sine waves, as I realized. Do I need to use a comparator + resistor included in AD985X breakout boards?

Should I use this amplifier?
http://www.k8iqy.com/miscell/aneous/18dblt1253ddsamplifier/lt1253ddsamp.htm

Thanks.

20

it makes no sense because sine wave is modulated out of little rectangles only to be converted back into a rectangle

Please explain.