This is the output of a three-phase generator. So, glue a bar magnet to the shaft of a small DC motor, and put three pickup coils around it. Pole pieces for the pickup coils are optional.
Use a PWM switch to run the motor, with a frequency-sensing feedback loop to generate the error signal. A '4046 can do the frequency-voltage conversion for you, off any of the phases. You might even be able to generate pulses on all the zero-crossings of the three phases, that'd give you six times the base frequency to lock the PLL to.
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R
Rich Grise
The OP finally made an appearance and says that the relay coils aren't being used to energize relays; they're evidently just the right size for OP to make a rotating magnetic field.
Cheers! Rich
J
John Devereux
[...]
+--------+ |ADUC7021|
+--------+
:)
John Devereux
J
Jim Thompson
I've been known to go super crude and use a shift register, resistors on each output, sum thru an OpAmp. On-chip I've even done this at
1GHz ;-) ...Jim Thompson
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Ding Dong! The Witch is Dead. Wicked Old Witch Pelosi! Hurrah!
R
Rich Grise
This is "crude?" I'd have thought it rather elegant, if you want to go through the tedium of selecting the right resistor values.
Cheers! Rich
J
John Devereux
The ADUC7021 was a sort of "cheat" - a joke - but I am starting to think it is probably the best solution. It's a single chip ARM, with 4 good 12 bit DACs and an internal 1% oscillator. There's code space for a 12 bit lookup table for each DAC, though at 10Hz it could calculate the waveform in real time!
John Devereux
D
dagmargoodboat
uld
een
Yep. If you want to get tricky you can use Don Lancaster's magic sinewaves or something similar to conjure up PWM waveforms that cancel the various harmonics, which makes the filtering even easier.
Yes. OTOH, you might even direct-drive the coils here, since they're being run off Vdd anyhow. That would save even the op-amp. It doesn't get any simpler than that.
-- Cheers, James Arthur
D
dagmargoodboat
y
tween
s,
All he needs to do is compute a reasonable, semi-optimal sequence in advance, then output it with efficient code.
The generator costs $0.50, one part, plus filters and drivers. It's really all pretty easy.
-- Cheers, James Arthur
D
dagmargoodboat
.
I
s
could
..
y
tween
s,
Belay that last part--the OP likely wants a clean magnetic field, which means PWM --> filters + coil drivers, as you said.
-- Cheers, James Arthur
B
Bill Sloman
he
nly
between
s
ips,
g
e
To approximate a 10Hz sine wave with was new mark to space ratio every
50usec, you need 500 mark-to-space ratios, and successive ratios aren't going to differ by more than one part in 637, so you want to code them to ten bits or better, and your pulse width timer wants to be clocked at at 20MHz or faster, all of which is starting to get difficult with $0.50 micro.
If you don't think about it in any detail.
-- Bill Sloman, Nijmegen
B
Bill Sloman
annel.
summing
lse none.
e use R2R ladders.
-+ =A0+---+
|-->PHASE 1
=A0+---+
+
+
=A0+---+
|-->PHASE 3
-+ =A0+---+
ne :-)
r
hatever,
And when I was, he had problems comprehending what I'd posted, leading to several quixotic quests on his part, trying to get me to admit that I'd screwed up because his interpretation of what I'd posted didn't make sense. It proved impossible to convince him that the problem lay with his interpretation (which couldn't possibly be wrong), rather than what I'd actually posted (which he couldn't possibly have misunderstood).
-- Bill Sloman, Nijmegen
B
Bill Sloman
--
=A0+---+
F|-->PHASE 1
=A0+---+
=A0
-+
-+
=A0+---+
F|-->PHASE 3
--
=A0+---+
Hewlett-Packard did it first. It's only crude if you don't use enough taps and don't get the resistor values right (including the windowing function). When you get it right it is a hardware implementation of a finite impulse response filter, and can be very give very nice results.
-- Bill Sloman, Nijmegen
J
John Fields
Exquisitely beautiful chip and, at less than $6 in qty 100 for the
Rolls-Royce version, it seems to be economical.
But, then there _is_ the cost of the development tools and the cost of
climbing the learning curve.
You're probably right if the OP is thinking of volume, but for a
one-off (or maybe even a million) I'll stick with my shift register
solution and either low-pass or band-pass the 10Hz output square waves
to get the required 3 phase sinusoidal outputs, depending on what he
needs.
So far he's been pretty sketchy about describing what he wants to do,
so unless he comes forth with what he's up to, I think he's just data
mining
R
Rich Grise
You might want to make the LUTs 384 or 768 bytes, so it's divisible by
:-)
Cheers! Rich
D
dagmargoodboat
e:
The
only
n between
was
ships,
th
big
-
ine
h
You're assuming interrupts and a timer for PWM. That's fatness. Don't do that. Use an ATMEGA part, or a few resistor-DACs if you can't figure out how to do without those crutches.
None of those are a big deal. Like I said, it's really pretty easy. No need for that pile of FPGAs with multiple supplies, etc.
I once generated a 1.2MHz direct-sequence spreading modulation, with data, real time, in an 8051. Several million were sold.
Of course I notice, but why would I harp on it? I prefer to learn from people's strengths rather than dwell on their weaknesses, for one thing. Besides, the only thing I've seen recently is that he thinks he skis faster.
-- Cheers, James Arthur
G
Grant
What sort of entrance fee though? Some sort of demo or development board, toolchain, programmer, etc?
Grant.
J
John Larkin
from
four
to
degree
of
Change the subject? Irrevelant? This is sci.electronics.design, you useless twit.
John
D
dagmargoodboat
No fair distracting him--he's busy proving a uC can't PWM a 10Hz sinewave.
"If you think you can do a thing or think you can't do a thing, you're right." --Henry Ford
-- Cheers, James Arthur
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