digital analog conversion

[Veronica Matthews]

Dear newsgroup community,

recently I came across the following challenge. There are several digital
values which I want to convert to analog signals. Ok then, no problem.
Simply D/A conversion! But after converting the signals the general set up
requires that these values should be held for about - let's say - a period
of 5 minutes with practically no droop (decay of the analog value) at best!
The D/A conversion itself takes place in a 1 MHz period, the values to be
set have to pend for about 5 minues. I guess a hold-element (capacitor and
op-amp) would be the obvious choice. But how should I dimension the
capacitance and how can I affect the droop? Is it realistic to expect
virtually no droop assuming an optimal configuration ? Isn't it, that with a
large time constant the charging time would be endless, too? Please help me,
if you can. I am almost become desperate. I need this for my graduation
report.

Thank you in advance and many greets
Veronica

 

[John Popelish]

Dear newsgroup community,

recently I came across the following challenge. There are several digital
values which I want to convert to analog signals. Ok then, no problem.
Simply D/A conversion! But after converting the signals the general set up
requires that these values should be held for about - let's say - a period
of 5 minutes with practically no droop (decay of the analog value) at best!
The D/A conversion itself takes place in a 1 MHz period, the values to be
set have to pend for about 5 minues. I guess a hold-element (capacitor and
op-amp) would be the obvious choice. But how should I dimension the
capacitance and how can I affect the droop? Is it realistic to expect
virtually no droop assuming an optimal configuration ? Isn't it, that with a
large time constant the charging time would be endless, too? Please help me,
if you can. I am almost become desperate. I need this for my graduation
report.

Thank you in advance and many greets
Veronica

Use a separate latch and D/A converter for each value. They will hold
as long as powered.

 

[Tilmann Reh]

recently I came across the following challenge. There are several digital
values which I want to convert to analog signals. Ok then, no problem.
Simply D/A conversion! But after converting the signals the general set up
requires that these values should be held for about - let's say - a period
of 5 minutes with practically no droop (decay of the analog value) at best!
The D/A conversion itself takes place in a 1 MHz period, the values to be
set have to pend for about 5 minues. I guess a hold-element (capacitor and
op-amp) would be the obvious choice. But how should I dimension the
capacitance and how can I affect the droop? Is it realistic to expect
virtually no droop assuming an optimal configuration ? Isn't it, that with a
large time constant the charging time would be endless, too? Please help me,
if you can. I am almost become desperate. I need this for my graduation
report.

It would be nice if you would stop posting this same question over
and over again in many different groups, while constantly ignoring all
those answers that were already given.

[If you want to reach people in different groups, do a (declared!)
crosspost to those (not too many) groups and set a proper follow-up.]

 

[Veronica Matthews]

It would be nice if you would stop posting this same question over
and over again in many different groups, while constantly ignoring all
those answers that were already given.

Wrong, not "over and over again" but in newsgroups that fit the topic. I
won't stop posting my questions just because a Tilmannreh tells me so! ;-)
The other point is that I am actually not ignoring the answers, but come
into discussion with all the people there. Please have a closer look before
you judge people. If you wear glasses, feel free to use them.
In correcting and imposing your will on me I wish you better luck next time!

 

[Winfield Hill]

Veronica Matthews wrote...

Wrong, not "over and over again" but in newsgroups that fit the topic. I
won't stop posting my questions just because a Tilmannreh tells me so! ;-)
The other point is that I am actually not ignoring the answers, but come
into discussion with all the people there. Please have a closer look before
you judge people. If you wear glasses, feel free to use them.
In correcting and imposing your will on me I wish you better luck next time!

John Popelish's advice is good, follow that.

 

[Rich Grise]

Dear newsgroup community,

recently I came across the following challenge. There are several digital
values which I want to convert to analog signals. Ok then, no problem.
Simply D/A conversion! But after converting the signals the general set up
requires that these values should be held for about - let's say - a period
of 5 minutes with practically no droop (decay of the analog value) at best!
The D/A conversion itself takes place in a 1 MHz period, the values to be
set have to pend for about 5 minues. I guess a hold-element (capacitor and
op-amp) would be the obvious choice. But how should I dimension the
capacitance and how can I affect the droop? Is it realistic to expect
virtually no droop assuming an optimal configuration ? Isn't it, that with a
large time constant the charging time would be endless, too? Please help me,
if you can. I am almost become desperate. I need this for my graduation
report.

Thank you in advance and many greets

Hi, Veronica.

Beware of two things here:

1. There are people who will make up all sorts of disinformation, because
there is a general attitude of disapproval of homework questions here.

2. The people in this group, being nerds, will trip over their tongues
to accommodate you because "Veronica" is a very hot name. <leer, snort>

So, all seriousness aside, if all you have to do is hold some specific
value that is to be DAC'd, why not latch the byte, store it indefinitely,
and convert it at your leisure?

Good Luck!
Rich

 

[Rich The Philosophizer]

Wrong, not "over and over again" but in newsgroups that fit the topic. I
won't stop posting my questions just because a Tilmannreh tells me so! ;-)
The other point is that I am actually not ignoring the answers, but come
into discussion with all the people there. Please have a closer look before
you judge people. If you wear glasses, feel free to use them.
In correcting and imposing your will on me I wish you better luck next time!

Well, I'll jump in here with my size thirteens, and say, hey, Veronica,
there are certain venues within which one would be well-advised to grow
a thick skin. ;-)

Don't sweat one nitpicker. And for heaven's sakes, don't take my word for
anything! I'm a known nut-case!

And don't worry about being corrected or overridden any more - I've
channeled Mother recently, and she says, It's OK, we've won, and it's
only a matter of time before Ahriman clues up.

Cheers!
Rich

 

[Tilmann Reh]

John Popelish's advice is good, follow that.

The same advice has been given her about a dozen times meanwhile.

 

[Tilmann Reh]

Wrong, not "over and over again" but in newsgroups that fit the topic. I
won't stop posting my questions just because a Tilmannreh tells me so! ;-)

Sorry - maybe due to some delays, some of your messages appeared after many
answers had already been given.
It would really have been better to crosspost and set a follow-up.

The other point is that I am actually not ignoring the answers, but come
into discussion with all the people there. Please have a closer look before
you judge people. If you wear glasses, feel free to use them.

Glasses already are at the right position.

Look at the good comments of Hans-Bernhard Broeker in comp.arch.embedded.
I suggest the discussion should be continued there, and not be spread
over many different groups.

 

[James Meyer]

Use a separate latch and D/A converter for each value. They will hold
as long as powered.

Or use a separate latch (random access memory) to store each digital
value and a single D/A converter multiplexed to as many sample and hold circuits
as necessary. Cycle through the stored digital values as fast as necessary to
ensure droop free outputs.

Jim

 

[Daniel Haude]

On Fri, 12 Nov 2004 11:18:54 +0100,

Wrong, not "over and over again" but in newsgroups that fit the topic. I
won't stop posting my questions just because a Tilmannreh tells me so! ;-)
The other point is that I am actually not ignoring the answers, but come
into discussion with all the people there.

It doesn't look like it, considering that the only post in this newsgroup
that you responded to is the only one that gives a non-technical answer.

You need to read up on the topics of both D/A conversion and Usenet.

The only sensible solution to your problem is to store the digital value,
not the analog one, like already suggested by John P.

--Daniel

 

[Ken Smith]

Or use a separate latch (random access memory) to store each digital
value and a single D/A converter multiplexed to as many sample and hold circuits
as necessary. Cycle through the stored digital values as fast as necessary to
ensure droop free outputs.

This can be done very effectively by having a small microcontroller in the
system to step through the channels. With an 8051, the code is very
simple.