3 phase from func.gen. IC

I've always been thinking. The mentally incapacitated, usually don't notice.

Don't fret, it'll probably take you a while to get this.

Never made a variable frequency generator with a uC before?

it's very easy. Look at DDS technology. Just an old idea with a new name on it and some alterations to make it possible for a wide range of output.

With 20 Mhz uC's you can get 1khz sine waves via pwm with no problem into a padded network that is unity buffered.

Even the slower ones can do that. Math isn't a problem, I just load a data table with the integral coefficients to index into, for fast computations of the PWM duty cycle.

And I have made a 3 phase 60 Hz reference generator with a PLL that did a 12 cycle latency sample. This was to replace an obsolete chip. (via an older generation PIC). The output wave form looked clean....

btw, there are some external components needed to polish this off, naturally. And if memory serves, I think microchip has newer uC's that makes this even easier now.

Have a good day..

=20

=20

Nothing at all. However average engineers find it difficult to maintain=20 proper phase relationships and maintain stable amplitude versus = frequency.

Yawn. You're as stupid as dimbulb. You'll never get that.

My favorite phrase since my MECL days... "Speed Kills" :-) ...Jim Thompson

I usually think of a DDS sinewave lookup table as being, well, sines, but you could just load the table with the PWM of the sines. A 20 MHz CPU - especially an ARM - doing 32-bit math could probably do 3-phase sines up to a couple hundred KHz with milli-Hz frequency resolution.

John

Yes, he and JT are unusually vulgar today. I figure they were cuddling for warmth and the shawl fell off their knees.

John

Ah, but you missed the whole point: PICs don't *have* DACs. To do it by PWM, you need big clocks.

Have you not noticed Jan's entire exploration of PICs? "How much can you do with a PIC and a minimum of support hardware?" DACs are support hardware, not internal, so they are excluded as much as possible.

Some hardware implementation of a count-and-compare PWM generator or sigma-delta DAC, locally PLL'd to some much higher clock (like 256MHz), and controlled by a microcontroller at much lower rates (4MHz would be enough), would be suitable. Alas, they don't make these, nor do they make PICs (or AVRs) with [parallel] DACs inside, so you're SOL as far as running the core at big MHz. The alternative is finding a uC which *does* have a DAC inside, but that directly violates the thesis: use a *PIC*.

Tim

Whatsa matter, John, can't you see reality?... You're a prissy-panted asshole. ...Jim Thompson

Professional courtesy response, I presume ?

My my, what vulgarity out of a prestige young man, like yourself.

I like your social candor, it has some of the most explicit, unique, qualities.

Have a good day and may your plasma eruptions be many..

PICs are mostly antiques. One of my guys is working with an eval board that has a sub-$1 ARM processor on board, with enough flash, ram, and i/o stuff to be useful. It could easily do DDS with 1-bit (software delta-sigma) DAC outputs at KHz sine wave rates.

John

The ARM cortex-m3 from st has 2 built-in DACs, that can both be driven using the DMA engine, with no software intervention at all other than setup (the DMA can fetch repeatedly from a table and loop back to the start). Doesn't do DDS, but doing it in software would be easy.

The one I've been playing with recently is about $5 in quantities. 512k flash, 64k ram, ADC, DAC, scads of timers, DMA engines that can interface with most of the internal devices, etc. Nice debug support using jtag.

You are right, PICs are antiques. Even their new 32 bit chip is an antique; it uses the MIPS core I was programming 12 years ago.

Regards, Bob Monsen

If you had, say, a 100 or 200 KHz periodic interrupt, the code to do

NXP and Marvell have some screamer ARMs with cache, ram, dram controllers, all sorts of peripherials, and 100M or Gbit MACs. Cheap.

John

Google "Scott Tee Transformer" and then figure out how to generate a sine wave in quadrature to the reference.

From my reply in the same thread,3/11/2010 03:03PM:

"Once you've got two sine waves in quadrature, getting three phase is simple. Just use a Scott-T transformer. These were once used for power applications, but since two phase power is almost extinct, they are now used for connecting servos that use synchros to those with resolvers."

Glad to see another old time power guy! :-)

--- Geez, John, one of us finding you wrong and the other agreeing with that finding doesn't represent "cuddling" in my book, just statement of, and agreement on, objective fact.

Of course being found wrong is "mea maxima culpa" when viewed through your deranged set of values and can't be allowed to coexist with what you hold precious; your infallibility, Mr. "Infinity only means something very large.", so you'll try to do whatever you can to fool all of the people all of the time even though all you do is fool yourself since you think you've gotten everyone to goose-step along with you.

JF