idealCircuit simulator

[Mike O'Dell]

these days, the Cortext M3 parts are no more expensive than
the Arduino CPU parts and they have a lot more computrons
to show for the effort.  There is at least one Arduino clone board
that uses a Cortex, I believe it's an STM32 family part. by "clone"
board, I mean that the cpu card is the same size and was designed
to use the Arduino "shields".

     -mo


On 1/5/13 7:02 PM, wb4jfi at knology.net wrote:
> Hello there Karl.  I did not see the LP filter design that you 
> mentioned, but I believe the type of filter is an elliptical, or Cauer 
> filter.  You can use the free filter design and analysis program from 
> aade.com to design them. I've used them for several years with DDS 
> designs.  The AD9850 is pretty old technology these days, but the 
> price is pretty good.  It's output DAC's resolution is not great, and 
> it's a power hog.  I was playing a lot with the AD9850, AD9851, 
> AD9832, AD9833, AD9834, AD9835 for several years, driving them with 
> PIC chips.  The newer AD995x and AD9912 are more iinteresting, as they 
> have better DAC resolution, higher clock rates, and lower power 
> requirements.  But, they have a harder package to use.
> Typically, you can design a Cauer filter to not only provide a 
> traditional low-pass function, but you can often tune the response for 
> maximum loss at the DDS clock frequency (sample rate).  That helps to 
> reduce the garbage seen from these older DDS devices.
> One thing to keep in mind is that programming these devices requires 
> 32-bit and sometimes 64-bit math, and sometimes even floating point.  
> The Arduino CPUs (except possibly the new Due) does not have a good 
> math library.  It only has "float" types, no doubles (which causes 
> poor accuracy).  Also, I've had problems (failures) in trying to use 
> long-long (64-bit) ints, even though that is supposedly implemented.  
> Using 32-bit long ints is problematic in doing the 
> frequency-tuning-words (FTW).  I'm having a similar problem 
> programming the Si570 with an Arduino, I had to give up on precise 
> calculations, and am using a "close-enough" approximation.
> Enjoy.
> 73,
> Terry, WB4JFI
> *From:* Karl W4KRL <mailto:W4KRL at arrl.net>
> *Sent:* Thursday, January 03, 2013 1:54 PM
> *To:* tacos at amrad.org <mailto:tacos at amrad.org>
> *Subject:* idealCircuit simulator
>
> Tacoistas,
>
> I ordered an AD9850 DDS Arduino shield on eBay for less than $6. It 
> should be here from Thailand at the end of the month.
>
> A quick reading of the application notes suggests that the output 
> should go through a 70MHz low pass filter for use in the 0 to 40MHz 
> range. There are several nice on-line filter designers:
>
> http://www.wa4dsy.net/filter/hp_lp_filter.html
>
> http://www.calculatoredge.com/electronics/bw%20pi%20low%20pass.htm
>
> But after looking at the low-res circuit jpg on eBay it turns out that 
> it has an on-board filter. The values are vaguely similar to what the 
> on-line designers calculate for a 7-pole Butterworth Pi but each 
> inductor is shunted with a small capacitor. I thought it would be 
> interesting to figure out what the filter was supposed to do and 
> looked unsuccessfully for an on-line circuit simulator. There is a 
> fair one sponsored by Digi-Key at http://www.partsim.com/simulator but 
> I found it so awkward to use that I gave up after drawing the circuit. 
> It did not produce any useful results.
>
> Then I came across idealCircuit at http://ic.sidelinesoft.com/
>
> The download is only 1.4MB and is free. There are probably a lot of 
> limitations but it looks good enough for quick general use. One 
> obvious drawback is the lack of part IDs. Maybe there is a work around 
> in the manual.
>
> I drew the filter and got a voltage and phase graph in just a few 
> minutes with zero frustration. The circuit and results are attached. 
> It seems to be a 70MHz low pass with some ripple and peaks near 
> cutoff. _Comments on the design and performance of the filter are 
> welcome. Why did they shunt the inductors with caps?_
>
> Happy New Year
>
> Karl W4KRL
>
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