T
Tareq Matar
Guest
Is there a way to convert to different signals with one ADC instead of using two separate converters?
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M
Maynard A. Philbrook Jr.
Guest
In article <d0e718f6-4ed2-44ff-a827-2ccf9c55e41b@googlegroups.com>,
tareqmatarr@gmail.com says...
Yup, you need an analog switch and it has to be switched via uC line or
what ever..
It switches, then a reading is taken. etc..
If you're trying to work with a high resolution ADC
and expect accurate readings you need to have a
way to calibrate between the two sources. Some
use a table of values in the uC others, use pots
on the board etc..
Jamie
tareqmatarr@gmail.com says...
Is there a way to convert to different signals with one ADC instead of using two separate converters?
Yup, you need an analog switch and it has to be switched via uC line or
what ever..
It switches, then a reading is taken. etc..
If you're trying to work with a high resolution ADC
and expect accurate readings you need to have a
way to calibrate between the two sources. Some
use a table of values in the uC others, use pots
on the board etc..
Jamie
J
John Larkin
Guest
On Sat, 16 Aug 2014 14:11:19 -0700 (PDT), Tareq Matar
<tareqmatarr@gmail.com> wrote:
>Is there a way to convert to different signals with one ADC instead of using two separate converters?
Put an analog multiplexer ahead of the ADC,, like an HC4051 or a DG408
sort of thing. Some ADCs have built-in multiplexers, AD7699 for
instance. uPs that have an internal ADC often include a mux to
digitize multiple inputs.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
<tareqmatarr@gmail.com> wrote:
>Is there a way to convert to different signals with one ADC instead of using two separate converters?
Put an analog multiplexer ahead of the ADC,, like an HC4051 or a DG408
sort of thing. Some ADCs have built-in multiplexers, AD7699 for
instance. uPs that have an internal ADC often include a mux to
digitize multiple inputs.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
T
Tareq Matar
Guest
i cant use a mux, i need those signals to be synchronized in order to obtain synchronized samples.
Is there another way to do that?
Best Regards,
Tareq Matar
Is there another way to do that?
Best Regards,
Tareq Matar
R
Randy Day
Guest
In article <01d9da63-cfc6-4cef-a8b6-4ca4b99974e6@googlegroups.com>,
tareqmatarr@gmail.com says...
If you expect a single converter to measure 2 or
more signals simultaneously, I don't think you can.
If by 'synchronized' you mean sampled within a few
tens of microseconds of each other, a mux solution
should be adequate.
If you mean to synchronize multiple samples with
adc's on a single chip, digikey lists devices with
up to 32 adc's on a simgle chip (DDC264).
HTH
--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
tareqmatarr@gmail.com says...
i cant use a mux, i need those signals to be synchronized in order to obtain synchronized samples.
Is there another way to do that?
If you expect a single converter to measure 2 or
more signals simultaneously, I don't think you can.
If by 'synchronized' you mean sampled within a few
tens of microseconds of each other, a mux solution
should be adequate.
If you mean to synchronize multiple samples with
adc's on a single chip, digikey lists devices with
up to 32 adc's on a simgle chip (DDC264).
HTH
--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
B
Bob Masta
Guest
On Sat, 16 Aug 2014 19:59:59 -0700 (PDT), Tareq Matar
<tareqmatarr@gmail.com> wrote:
that you strobe all at once to acquire one multi-sample.
The separate input samples are held (on charged capacitors)
for subsequent reading via a MUX and ADC.
Another approach would be to have multiple ADCs that share
the same clock and are strobed at the same time. Then you
could use a *digital* MUX to read them one at a time into
your processor.
However, I suspect that you can get away with a normal
MUX-ADC system if you take the inter-sample delays into
account when computing relative phase between channels.
Obviously, the sample rate will need to be high enough such
that there is much less than one cycle's-worth of delay
between channels at the highest frequency of interest, to
prevent phase ambiguity. But you pretty much need to do
that anyway for ordinary anti-aliasing.
Best regards,
Bob Masta
DAQARTA v7.60
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE Signal Generator, DaqMusiq generator
Science with your sound card!
<tareqmatarr@gmail.com> wrote:
You can have multiple sample-and-holds, one for each input,i cant use a mux, i need those signals to be synchronized in order to obtain synchronized samples.
Is there another way to do that?
that you strobe all at once to acquire one multi-sample.
The separate input samples are held (on charged capacitors)
for subsequent reading via a MUX and ADC.
Another approach would be to have multiple ADCs that share
the same clock and are strobed at the same time. Then you
could use a *digital* MUX to read them one at a time into
your processor.
However, I suspect that you can get away with a normal
MUX-ADC system if you take the inter-sample delays into
account when computing relative phase between channels.
Obviously, the sample rate will need to be high enough such
that there is much less than one cycle's-worth of delay
between channels at the highest frequency of interest, to
prevent phase ambiguity. But you pretty much need to do
that anyway for ordinary anti-aliasing.
Best regards,
Bob Masta
DAQARTA v7.60
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE Signal Generator, DaqMusiq generator
Science with your sound card!
R
RobertMacy
Guest
On Sat, 16 Aug 2014 14:11:19 -0700, Tareq Matar <tareqmatarr@gmail.com>
wrote:
see if you can get a schematic for a 'good' soundcard. they do two
channels, useable 10Hz to 85kHz at 24bits with one ADC, and even 8
channels at slower rates up to 20kHz.
If you're developing a product, you can license a working design from a
manufacturer. Someone like Creative Labs will negotiate to license you
their design, but at the volume pricing they offer for the OEM soundcards,
may not be worthwhile.
wrote:
Is there a way to convert to different signals with one ADC instead of
using two separate converters?
see if you can get a schematic for a 'good' soundcard. they do two
channels, useable 10Hz to 85kHz at 24bits with one ADC, and even 8
channels at slower rates up to 20kHz.
If you're developing a product, you can license a working design from a
manufacturer. Someone like Creative Labs will negotiate to license you
their design, but at the volume pricing they offer for the OEM soundcards,
may not be worthwhile.
M
Maynard A. Philbrook Jr.
Guest
In article <MPG.2e59e8f4612ff2ff989683@202.177.16.121>,
randy.day@sasktel.netx says...
But aren't those muxed also?
Jamie
randy.day@sasktel.netx says...
In article <01d9da63-cfc6-4cef-a8b6-4ca4b99974e6@googlegroups.com>,
tareqmatarr@gmail.com says...
i cant use a mux, i need those signals to be synchronized in order to obtain synchronized samples.
Is there another way to do that?
If you expect a single converter to measure 2 or
more signals simultaneously, I don't think you can.
If by 'synchronized' you mean sampled within a few
tens of microseconds of each other, a mux solution
should be adequate.
If you mean to synchronize multiple samples with
adc's on a single chip, digikey lists devices with
up to 32 adc's on a simgle chip (DDC264).
HTH
--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
But aren't those muxed also?
Jamie
J
John Larkin
Guest
On Sat, 16 Aug 2014 19:59:59 -0700 (PDT), Tareq Matar <tareqmatarr@gmail.com>
wrote:
The classic way to do this is to have multiple analog sample-and-hold circuits,
followed by a multiplexed ADC. That could be hard or easy, depending on your
unstated speed and accuracy requirements.
There are some simultaneous-sampling multi-channel ADC chips that do this.
I've done electric meters where I wanted to "simultaneously" sample voltage and
current waveforms. One trick is to just mux and digitize, which gives a time
sampling error, but tweak the phase shift of the input amplifiers to correct for
the time error. That only works at one frequency, of course. A proper delay line
could do this wideband.
You can also in some cases alternate sampling
AB...BA....AB....BA
which statistically removes the sampling skew error. I've done that in electric
meters too.
If you oversample, you can do math on the samples to emulate simultaneous
sampling.
Or, since ADCs are cheap these days, use lots of them.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
wrote:
i cant use a mux, i need those signals to be synchronized in order to obtain synchronized samples.
Is there another way to do that?
Best Regards,
Tareq Matar
The classic way to do this is to have multiple analog sample-and-hold circuits,
followed by a multiplexed ADC. That could be hard or easy, depending on your
unstated speed and accuracy requirements.
There are some simultaneous-sampling multi-channel ADC chips that do this.
I've done electric meters where I wanted to "simultaneously" sample voltage and
current waveforms. One trick is to just mux and digitize, which gives a time
sampling error, but tweak the phase shift of the input amplifiers to correct for
the time error. That only works at one frequency, of course. A proper delay line
could do this wideband.
You can also in some cases alternate sampling
AB...BA....AB....BA
which statistically removes the sampling skew error. I've done that in electric
meters too.
If you oversample, you can do math on the samples to emulate simultaneous
sampling.
Or, since ADCs are cheap these days, use lots of them.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
R
Randy Day
Guest
In article <MPG.2e5a8e1ecf0d93939899e0@news.eternal-september.org>,
jamie_ka1lpa@charter.net says...
[snip]
Yes, each of the 32 adc's has a 2:1 mux,
but if the OP needs 32 channels or less,
he can leave the mux on one channel.
Sure it gives up 1/2 the functionality
of the chip, but it gives him his
simultaneous sampling.
I'd expect the same would hold true of
the smaller (<32 adc) devices as well;
the OP didn't mention how many samples
he was trying for.
jamie_ka1lpa@charter.net says...
[snip]
If you mean to synchronize multiple samples with
adc's on a single chip, digikey lists devices with
up to 32 adc's on a simgle chip (DDC264).
HTH
But aren't those muxed also?
Yes, each of the 32 adc's has a 2:1 mux,
but if the OP needs 32 channels or less,
he can leave the mux on one channel.
Sure it gives up 1/2 the functionality
of the chip, but it gives him his
simultaneous sampling.
I'd expect the same would hold true of
the smaller (<32 adc) devices as well;
the OP didn't mention how many samples
he was trying for.