DDS Evaluation Board from Analog Devices

[D from BC]

I'm checking out the AD9834EB evaluation board from Analog Devices.

Digikey price: $158.61can
Comes with software.
Picture on:
http://rocky.digikey.com/WebLib/Analog Devices/Web Photo/New Photos/EVAL-AD9834EB.jpg
See crystal frequency: 75Mhz

Software screenshots on
http://www.analog.com/UploadedFiles/Evaluation_Boards_Tools/137452056EVAL_AD9834EB.pdf
Sweep function!
Sine and triangle selection too.

Datasheet foutmax: 37.5Mhz
AD9834 Datasheet on:
http://www.analog.com/UploadedFiles/Data_Sheets/783446377AD9834.pdf

For a poormans function generator...would the performance be worth the
money?


D from BC

 

[[email protected]]

I'm checking out the AD9834EB evaluation board from Analog Devices.

Digikey price: $158.61can
Comes with software.
Picture on:http://rocky.digikey.com/WebLib/Analog Devices/Web Photo/New Ph...
See crystal frequency: 75Mhz

Software screenshots onhttp://www.analog.com/UploadedFiles/Evaluation_Boards_Tools/137452056...
Sweep function!
Sine and triangle selection too.

Datasheet foutmax: 37.5Mhz
AD9834 Datasheet on:http://www.analog.com/UploadedFiles/Data_Sheets/783446377AD9834.pdf

For a poormans function generator...would the performance be worth the
money?

D from BC

That chip seems to have some sort of differential current mode output,
would that be useful to you?
I'd try to put some sort of buffer on there to get the usual voltage
output into 50 ohms. It would also protect the chip from potential
damage.
I note the crunky parallel port on there, I would prefer USB, but what
can you do?
Kind of weird for a chip that has a serial interface.

To me it seems like you'd learn a lot and end up with a quite handy
device.

I find the price too high though. AD usually includes the layout in
their datasheets. Just toss the file to Olimex and get a board made
for 35$ and buy the chip for 10$.

 

[D from BC]

That chip seems to have some sort of differential current mode output,
would that be useful to you?
I'd try to put some sort of buffer on there to get the usual voltage
output into 50 ohms. It would also protect the chip from potential
damage.
I note the crunky parallel port on there, I would prefer USB, but what
can you do?
Kind of weird for a chip that has a serial interface.

To me it seems like you'd learn a lot and end up with a quite handy
device.

I find the price too high though. AD usually includes the layout in
their datasheets. Just toss the file to Olimex and get a board made
for 35$ and buy the chip for 10$.

I noticed that. I probably would make an output section suitable for
the work I do. Op amp otta do.

I suspect the software programmer found parallel port interfacing
easier than the USB interface in Windoze XP.

I don't think the artwork drawing at the bottom of
http://www.analog.com/UploadedFiles/Evaluation_Boards_Tools/137452056EVAL_AD9834EB.pdf
is good enough for Olimex It's all pixelated...It'll need work

Yup...I wish it was cheaper..like $50.00!
A stable accurate PC controlled 37Mhz sine/triangle sweep generator
for $50.00 would be wonderful.

D from BC

 

[Ecnerwal]

I'm checking out the AD9834EB evaluation board from Analog Devices.

Digikey price: $158.61can ....
For a poormans function generator...would the performance be worth the
money?

I think your earlier idea of actually rolling one makes far more sense.
Here you are definitely in the ballpark of "as much money spent as a
standalone", it's not a complete unit, (slap an op amp on may not be
quite enough for quality output drive over the full frequency range) and
you are at the mercy of keeping a computer with centronics port running
- not a big deal now, but in 5-10 years? They are dropping off the newer
computers.

Design something with USB or Ethernet interface, and make it good enough
to sell - then you should be money ahead. Otherwise, your $158.61
Canadian will go a long ways towards getting you a fully functional,
fully built unit from either Asia or *B*y (or from Asia via *B*y).

 

[john jardine]

I'm checking out the AD9834EB evaluation board from Analog Devices.

Digikey price: $158.61can
Comes with software.
Picture on:
http://rocky.digikey.com/WebLib/Analog Devices/Web Photo/New Photos/EV
AL-AD9834EB.jpg
See crystal frequency: 75Mhz

Software screenshots on
http://www.analog.com/UploadedFiles/Evaluation_Boards_Tools/137452056EVAL_AD
9834EB.pdf
Sweep function!
Sine and triangle selection too.

Datasheet foutmax: 37.5Mhz
AD9834 Datasheet on:
http://www.analog.com/UploadedFiles/Data_Sheets/783446377AD9834.pdf

For a poormans function generator...would the performance be worth the
money?


D from BC

Personally, I'd say more trouble than they're worth. You buy the board, then
still have to add on a fast differential amplifier, then (most importantly)
a decent low pass filter and then probably another amp/buffer. End up with
another PCB just to get the sine out and usable.
What's never mentioned in the datasheets is how impossibly useless the
output waveform is at maximum operating frequency. That "37.5MHz" is
theoretical only. For good useable sines, something like 1/8th the clock
frequency should be considered a max (eg 10MHz).
Triangle, what is that used for?. Forget the square output as well. The
basic DDS generating mechanism becomes so visible on squares that a 'scope
can't even lock on to some particular frequencies. (observations based on a
slower AD9833 I though would be OK as a function gen')
Would suggest getting any serial type (clock data) DDS chip and wiring it
yourself. Only needs 3 wires from the LPT and the frequency programming you
can do yourself. Software will probably be more reliable than what AD
supplies!.

 

[D from BC]

I think your earlier idea of actually rolling one makes far more sense.
Here you are definitely in the ballpark of "as much money spent as a
standalone", it's not a complete unit, (slap an op amp on may not be
quite enough for quality output drive over the full frequency range) and
you are at the mercy of keeping a computer with centronics port running
- not a big deal now, but in 5-10 years? They are dropping off the newer
computers.

Design something with USB or Ethernet interface, and make it good enough
to sell - then you should be money ahead. Otherwise, your $158.61
Canadian will go a long ways towards getting you a fully functional,
fully built unit from either Asia or *B*y (or from Asia via *B*y).

On the + side....
I have a computer here with a useless parallel port. So, it can be
dedicated to interfacing with the DDS.

On the - side...
Yup...that $158 is in the ballpark of most EEbbaayy generators which
are complete.
This is a spoiler.

It's now a decision of make my own PCB + add what's missing or get
something off Eebaayy.


D from BC

 

[[email protected]]

This is a spoiler.

It's now a decision of make my own PCB + add what's missing or get
something off Eebaayy.

D from BC

Get something off eBay. My strategy is to have the patience of a
spider.
Spin a web of email warnings and wait for a good price.
Don't wait to actually *need* the device.
If you buy when you don't need it, you
1) don't care if you lose it
2) can underbid

I have a lab of stuff just waiting for me to actually build stuff
again.

 

[D from BC]

Personally, I'd say more trouble than they're worth. You buy the board, then
still have to add on a fast differential amplifier, then (most importantly)
a decent low pass filter and then probably another amp/buffer. End up with
another PCB just to get the sine out and usable.
What's never mentioned in the datasheets is how impossibly useless the
output waveform is at maximum operating frequency. That "37.5MHz" is
theoretical only. For good useable sines, something like 1/8th the clock
frequency should be considered a max (eg 10MHz).
Triangle, what is that used for?. Forget the square output as well. The
basic DDS generating mechanism becomes so visible on squares that a 'scope
can't even lock on to some particular frequencies. (observations based on a
slower AD9833 I though would be OK as a function gen')
Would suggest getting any serial type (clock data) DDS chip and wiring it
yourself. Only needs 3 wires from the LPT and the frequency programming you
can do yourself. Software will probably be more reliable than what AD
supplies!.

Yup.. I'll still be making a board for an output amplitude control
section. So..I might as well do the PCB for the DDS chip anyways.
I don't even need a connector on the PCB. I can hack off some old
parallel cable and solder it direct.

I was thinking of using the triangle wave to make a variable duty
square wave generator section.

I am thinking about the filtering.


D from BC

 

[[email protected]]

I was thinking of using the triangle wave to make a variable duty
square wave generator section.

I believe this is in the chip already. There is a comparator. (going
from memory here).

I am thinking about the filtering.

D from BC

I think this will be the most work...

 

[D from BC]

Get something off eBay. My strategy is to have the patience of a
spider.
Spin a web of email warnings and wait for a good price.
Don't wait to actually *need* the device.
If you buy when you don't need it, you
1) don't care if you lose it
2) can underbid

I have a lab of stuff just waiting for me to actually build stuff
again.

Ahh yah..it's nice to play on Eebayy without desperation

Well...the AD eval board was tempting...

AD Eval Board |Ebbaayy
---------------------------+-------------------------
I know what I getting. |It could be broken.
Negligible shipping cost(1)|Around $65.00 by USPS
Missing electronics |Complete
Needs R&D time |Ready to use
Needs benchtop PC |No PC required
New electronics |Possibly old electronics

(1) It wouldn't change my shipping cost if the eval board was included
in my usual Digikey parts order.


D from BC

 

[Frank Buss]

Yup.. I'll still be making a board for an output amplitude control
section. So..I might as well do the PCB for the DDS chip anyways.
I don't even need a connector on the PCB. I can hack off some old
parallel cable and solder it direct.

I was thinking of using the triangle wave to make a variable duty
square wave generator section.

I am thinking about the filtering.

Any news on your DDS project? I'm building something similar, see my first
try:

http://it4systems.de/SignalGenerator/doc/index.html

You can get inexpensive FPGA development boards, like this for about $60:

http://www.enterpoint.co.uk/component_replacements/drigmorn1.html

RS232 is already integrated.

I've used another board, because I've used it for other projects already
and it has a DAC integrated:

http://www.xilinx.com/products/devkits/HW-SPAR3E-SK-US-G.htm

The advantage compared to the Analog Devices chip is that you can do more
with it, e.g. generating digital patterns, controlled by the PC over the
RS232 port etc., without the need for additional chips.

Adding something like the AD5445 provides a 20 MHz, 12 bit, analog output
(but a fast opamp after the DAC would be a good idea, like described in the
application note). I think all parts, including some housing, would cost
less than $100 and you can program any special functions you need in the
FPGA, which is impossible if you buy something ready-made (or at least
costs much more).

 

[D from BC]

Any news on your DDS project? I'm building something similar, see my first
try:

http://it4systems.de/SignalGenerator/doc/index.html

You can get inexpensive FPGA development boards, like this for about $60:

http://www.enterpoint.co.uk/component_replacements/drigmorn1.html

RS232 is already integrated.

I've used another board, because I've used it for other projects already
and it has a DAC integrated:

http://www.xilinx.com/products/devkits/HW-SPAR3E-SK-US-G.htm

The advantage compared to the Analog Devices chip is that you can do more
with it, e.g. generating digital patterns, controlled by the PC over the
RS232 port etc., without the need for additional chips.

Adding something like the AD5445 provides a 20 MHz, 12 bit, analog output
(but a fast opamp after the DAC would be a good idea, like described in the
application note). I think all parts, including some housing, would cost
less than $100 and you can program any special functions you need in the
FPGA, which is impossible if you buy something ready-made (or at least
costs much more).

I put the DDS project on hold until I finish my other projects.

I was interested in comparing:
A DIY DDS poorman generator
versus
spending ~$300.00 on some possibly broken E*bay generator made in
~1992.


D from BC

 

[Frank Buss]

I put the DDS project on hold until I finish my other projects.

I was interested in comparing:
A DIY DDS poorman generator
versus
spending ~$300.00 on some possibly broken E*bay generator made in
~1992.

I just read in a German newsgroup about this project:

http://www.myplace.nu/avr/minidds/index.htm

A really inexpensive, but good DDS generator, if you don't need frequencies
higher than 200kHz.

 

[Ben Jackson]

Any news on your DDS project? I'm building something similar, see my first
try:

http://it4systems.de/SignalGenerator/doc/index.html

You should look into DSP filtering. There are a lot of better ways to
upsample your sparse sin table than linear interpolation.

 

[Frank Buss]

You should look into DSP filtering. There are a lot of better ways to
upsample your sparse sin table than linear interpolation.

Yes, but I wonder if I need it. I could do cubic interpolation, but if I
have 12 bits output, only, it will be better just to store as many samples
with 12 bit width as needed to avoid more than one LSB change in adjacent
values. This would give perfect results without any interpolation at all.

But if I want 24 bit output, it might be more accurate to use something
like CORDIC to calculate the values, or polynomial approximation, if I have
some hardware multiplier or if I use a fast DSP, because interpolation
produces not mathematically exact sine values.

 

[Frank Buss]

I was interested in comparing:
A DIY DDS poorman generator
versus
spending ~$300.00 on some possibly broken E*bay generator made in
~1992.

Here is the new version of my DIY generator (ok, you'll need the Spartan3E
starter kit, too, but at least all the VHDL and C code is DIY)

http://www.frank-buss.de/SignalGenerator/

Now you can compare it to the $300 generator

 

[D from BC]

Here is the new version of my DIY generator (ok, you'll need the Spartan3E
starter kit, too, but at least all the VHDL and C code is DIY)

http://www.frank-buss.de/SignalGenerator/

Now you can compare it to the $300 generator

Interesting... Originally, I was thinking of just downloading the
control app from analog devices and building my own DDS board based on
an Analog devices DDS chip.

But source code is better to customize and augment.


D from BC