Need DDS module, 2nd round

If by 'operating frequency under 10kHz' you mean the output frequency doesn't exceed 10kHz a fast microcontroller and a DAC (codec) should be more than sufficient. It doesn't sound like its rocket science to me...

But it is to me, I am an analog guy who knows barely enough C and assembler to be dangerous. Plus there ain't much time, I need some module that I can simply plop in and connect. The one in the link would be ideal if the modulator input weren't be dead.

Have you by any chance looked at National Instruments for signal generators, or for similar instruments or vendors?

I suppose you're looking for something stand-alone, though, not something that needs an umbilicus to a computer in order to function.

I guess they thought they could re-program the DDS fast enough / on the fly to get a glitch-free output. How much time do you have?

hat

DDS outputs are intrinsicly glitch-free - what you change is the number added to the phase accumulator on each step, and the stair-case approximation to the sine wave remains continuous, though the cycle - you are just changing the spacing of the treads..

Joerg should be able to sweep his sine wave pretty smoothly by incrementing/decrementing the last digit of his frequency-setting number frequently. Whether he can do it frequently enough is another question. He might have to program a PAL to do it for him.

Use a laptop ?>:-} ...Jim Thompson

hat

it should be possible, I just looked at the code it is just a single file (arduino Sketch) and a library for the lcd. The SPI to the DDS is bit banged a 16MHz should be able to do that quite fast

The schematic shows JP4 connected to ADC0 ac coupled with 4.7u cap and

so everything needed is there I think, all that is need is a timer interrupt to read the adc and update the DDS

-Lasse

-Lasse

This will do it, but it's overkill, roughly 100x your probable budget.

If you wanted to roll your own, it would take a small FPGA and a DAC.

That depends on whether the DDS is reset or not when the frequency setting is updated. There has to be a reason the designers at iteadstudio didn't implement the modulation. If it where simple they would have implemented it.

As I said, about 100Hz is the max sweep cycle frequency. So a few kHz update rate should do. Normally that isn't a problem with a DDS chip.

If necessary I could do it that way. But I am not really a good programmer. Ideall would be a module that has FM modulation or sweep. It doesn't have to be DDS, just stable and not too large. Ripping it out of a function generator is ok as well, as long as it's not much more than two cigarette packs or so in size.

Actually, there will be a netbook involved and I'll probably program the SCADA stuff on that myself. I believe they don't make the Samsung NC-10 anymore, but it'll be something like that.

Haven't found anything useful for this application.

Yup. Something that can be plopped into my RF board and control two frequencies (so two of those modules are needed). SPI or RS232, power supply, output, modulation input.

Yep, that sure would be overkill :-)

That's what I want to avoid, I've got enough on my plate as it is. If I really can't find a module I'll buy function generators and hack them apart on arrival, prying their main boards out. That would make my circuit board the size of a large family pizza, but man's gotta do what man's gotta do.

ing

hip

ewhat

ld

if you don't need external input it is even easier, if I had the HW I'd give it a try

do you really need the display and the controls or could you do with few preprogrammed waveforms/sweeps/frequencies on an easy to get dev-board with a few buttons added?

-Lasse

-Lasse

ng

ip

what

use the a sound card, possible external usb?

-Lasse

I need the input because it'll be used in a loop. It will actually become a glorified dipmeter. The phase response at the input of an LC lowpass filter will be measured and then this becomes the error signal in a PID loop. The PID loops adjusts the frequency of the DDS (or whatever other sine wave generator) so the phase remains constant even when the lowpass components change their values.

A display would be nice but I could also roach on a frequency counter. The output has to be sine wave, can't easily filter that because the thing has to work in frequency ranges I won't know up front. Being able to set the base frequency locally would be very helpful.

Theoretically, yes. But since this whole thing will sit inside a PID loop I'd then have to process the error signal (a phase information measured in my box) in the PC. Meaning lots of code writing and that's what I am trying to avoid as much as possible.

at 10kHz almost any mcu with a dac would do

-Lasse