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Digital storage func. gen.

M

Mark Steinberg

Jan 1, 1970
0
I would like to build a "function generator" that will digitally store
a single cycle of 5-10 individual sinewaves, each with a frequency
between 5Hz-500Hz, and play any or all back continuously on demand.

It must be stand-alone and battery powered, ie. not PC or soundcard
based. However, a PC could be involved in generating the SW's to be
stored. But note the lower limit will not pass a soundcard.

I have no special requirements regarding resolution, voltage or
current output, other than the sinewaves look as much like a continous
sinewave on a CRO as is possible without going to extremes.

IOW I am open to suggestions regarding trade-offs between precision
and practicality.

What would be the most effective design path to follow for this,
stressing minimum complexity.

How would the sinewaves be loaded into the storage medium?

Thanks for any ideas.

Mark
 
F

Frank Bemelman

Jan 1, 1970
0
Mark Steinberg said:
I would like to build a "function generator" that will digitally store
a single cycle of 5-10 individual sinewaves, each with a frequency
between 5Hz-500Hz, and play any or all back continuously on demand.

It must be stand-alone and battery powered, ie. not PC or soundcard
based. However, a PC could be involved in generating the SW's to be
stored. But note the lower limit will not pass a soundcard.

I have no special requirements regarding resolution, voltage or
current output, other than the sinewaves look as much like a continous
sinewave on a CRO as is possible without going to extremes.

IOW I am open to suggestions regarding trade-offs between precision
and practicality.

What would be the most effective design path to follow for this,
stressing minimum complexity.

How would the sinewaves be loaded into the storage medium?

This is cheap:
http://www.myplace.nu/avr/minidds/

You could modify the software a bit, to get your 5-10 different
preset frequencies. No need to hook it up to a PC all the time.
 
R

Rene Tschaggelar

Jan 1, 1970
0
Mark said:
I would like to build a "function generator" that will digitally store
a single cycle of 5-10 individual sinewaves, each with a frequency
between 5Hz-500Hz, and play any or all back continuously on demand.

It must be stand-alone and battery powered, ie. not PC or soundcard
based. However, a PC could be involved in generating the SW's to be
stored. But note the lower limit will not pass a soundcard.

I have no special requirements regarding resolution, voltage or
current output, other than the sinewaves look as much like a continous
sinewave on a CRO as is possible without going to extremes.

IOW I am open to suggestions regarding trade-offs between precision
and practicality.

What would be the most effective design path to follow for this,
stressing minimum complexity.

If it is just for sinewaves, I suggest the use of a DDS.
Does sine nicely, from zero to several MHz, with uHz
resolution. Have a look at the AD9833
http://www.analog.com/en/prod/0,,770_843_AD9833,00.html

Rene
 
R

Rich Grise

Jan 1, 1970
0
I would like to build a "function generator" that will digitally store
a single cycle of 5-10 individual sinewaves, each with a frequency
between 5Hz-500Hz, and play any or all back continuously on demand.

It must be stand-alone and battery powered, ie. not PC or soundcard
based. However, a PC could be involved in generating the SW's to be
stored. But note the lower limit will not pass a soundcard.

I have no special requirements regarding resolution, voltage or
current output, other than the sinewaves look as much like a continous
sinewave on a CRO as is possible without going to extremes.

IOW I am open to suggestions regarding trade-offs between precision
and practicality.

What would be the most effective design path to follow for this,
stressing minimum complexity.

How would the sinewaves be loaded into the storage medium?

Thanks for any ideas.

You can't get much simpler than an ICL8038 (or modern-day equivalent) and
5 - 10 capacitors. :)

Or, a counter, PROM, and DAC, amplifier optional. ;-)

Or, one of those newfangled single-chip thingies. ;-)

Good Luck!
Rich
 
M

mike

Jan 1, 1970
0
Mark said:
I would like to build a "function generator" that will digitally store
a single cycle of 5-10 individual sinewaves, each with a frequency
between 5Hz-500Hz, and play any or all back continuously on demand.

It must be stand-alone and battery powered, ie. not PC or soundcard
based. However, a PC could be involved in generating the SW's to be
stored. But note the lower limit will not pass a soundcard.

I have no special requirements regarding resolution, voltage or
current output, other than the sinewaves look as much like a continous
sinewave on a CRO as is possible without going to extremes.

IOW I am open to suggestions regarding trade-offs between precision
and practicality.

What would be the most effective design path to follow for this,
stressing minimum complexity.

How would the sinewaves be loaded into the storage medium?

Thanks for any ideas.

Mark
At the risk of sounding like a broken record...What are you trying to
accomplish? You specified "Function Generator" but only talked about
sine waves. What did you really mean??? Do you need triangles and squares?

If you need sine fidelity, use a triangle and diode shaper.

I set out to build a DDS function generator around a PIC processor.
I was really impressed at first. Sine waves looked nice on the spectrum
analyzer, even tho only 8-bit. But when I looked in time domain, I was
horrified. There are some interesting transient anomalies, especially
where the cycle length is one different from the number of stored
samples. Yes, you can filter anything and get a sinewave, but at 5 Hz.
that's gonna be some big filter.
And triangles and square waves weren't even close to being what they
should be. You can have sine wave points moving all around and filter
'em. Won't work for squares.

So, do you really need a whole function generator, or just sinewaves?
Purity? Can you stand AC coupled output?
Amplitude range?
Noise tolerable?
Harmonics vs noise vs FM?

The more you think about it the better you're gonna like triangles
and diodes. The single-chip analog function generators should work fine
at these frequencies. You can get reasonable (depending on your
definition) repeatability with digitally controlled current sources.
You're only asking for 500:1 range.
mike



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Bunch of stuff For Sale and Wanted at the link below.
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J

john jardine

Jan 1, 1970
0
Mark Steinberg said:
I would like to build a "function generator" that will digitally store
a single cycle of 5-10 individual sinewaves, each with a frequency
between 5Hz-500Hz, and play any or all back continuously on demand.

It must be stand-alone and battery powered, ie. not PC or soundcard
based. However, a PC could be involved in generating the SW's to be
stored. But note the lower limit will not pass a soundcard.

I have no special requirements regarding resolution, voltage or
current output, other than the sinewaves look as much like a continous
sinewave on a CRO as is possible without going to extremes.

IOW I am open to suggestions regarding trade-offs between precision
and practicality.

What would be the most effective design path to follow for this,
stressing minimum complexity.

How would the sinewaves be loaded into the storage medium?

Thanks for any ideas.

Mark

Looks like you'll need 10 similar channnels. I'd be inclined just to store
10 "time" numbers. Have a constant speed main clock and clock out square
waves at the wanted frequencies. Then ... 3rd order filter (one opamp) each
output to a useable sine wave.
regards
john
 
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