Lowest price USB 2.0 full speed DAQ for $49 or up

[Winfield Hill]

Mike Harrison wrote...

Audio AD/DA converters are not typically optimised (or sometimes even
characterised) for DC performance - things like offset drift may be
very much poorer than 24 bit performance - you should read the datasheet
carefully if DC matters to you.

That's correct. The ADC I had in mind is a audio stereo delta-sigma A-D
that easily generates an optical SPDIF signal, that I use with a USB-link
SPDIF receiver. This 24-bit ADC operates to 200kHz. Its DC performance
isn't stellar, but I could have chosen another part with nearly identical
24-bit performance that's designed and specified as an industrial ADC with
good DC specs. However it's not as easily used with optically-transmitted
SPDIF data streams, which I have found to be very appealing. These parts
are quite inexpensive, under $15, and most of them would make better low-
cost DAQs than the slow, low-resolution stuff under discussion here, IMHO.

 

[Too_Many_Tools]

A question for the group...what are the available products for the
market segment that this product is trying to address?

TMT

 

[Jonathan Westhues]

HYTEK wrote...

I still object to your calling 32kS/s "full speed"

Maybe they meant that it uses full speed USB (vs. low or high speed; that
determines the kind of signaling that is used). Of course that just
determines how much bandwidth you have available; it doesn't mean that you
have to use it all.

I'm not really sure how you would make it that slow. They said somewhere
else that they used interrupt transfers, and I think that would help a lot.
The classical thing to do when you don't want to write a WDM driver is to
enumerate as an HID device, which allows you to use a Microsoft-provided
..sys file but (as far as I know) forces you to use interrupt transfers. It
is convenient--I have done it--but it is very wasteful.

You could make one of these things out of an AT91SAM7S32, and just use the
on-board A/Ds. They are only 10-bit, but they are reasonably fast (384
ksamples/s). If you were smart with the software, then I think you could
actually get that. The part costs 4.50 in hundreds. The terminal strips and
stuff would probably cost more.

Jonathan

 

[HYTEK]

Well, I'm sorry if for any reason that our product makes you so upset
(you sounded very upset). But anyway, I think if you can make a "low
cost" 24 bit DAQ, it will be very useful. But just keep in mind (sorry,
I really don't intend to teach anybody here, but I thought this
information maybe useful to some people)
1. The USB transfer method for audio may not be suitable for a DAQ, you
can find those information in books about USB. That is why you see the
audio (or even video) signal can be transfered a lot faster, but it may
not be suitable to a DAQ. I have explained a little bit in my other
reply.
2. Don't compare the sampling rate of a burst mode DAQ to a streaming
mode DAQ, with burst mode you definitely can sample a lot fast, but
that does not mean that you can transfer them as fast as they sample.

There are many other usb daqs on the market, the full speed interface
works from 10ks/s to 50ks/s (normally 12bit), so our iUSBDAQ is not
really that slow considering it's price.

And of course, everybody is welcome to try out their own design of usb
daq, but you will also have to provide software in order to compete in
the market, so for our effort and this low price, I don't think why
people are upset about it, all we do can only benefit users.

Irene

 

[Jonathan Westhues]

1. The USB transfer method for audio may not be suitable for a DAQ, you
can find those information in books about USB. That is why you see the
audio (or even video) signal can be transfered a lot faster, but it may
not be suitable to a DAQ. I have explained a little bit in my other
reply.

Did you actually see problems when you used isochronous transfers? It was my
impression that USB, without any reliable delivery mechanism, already gives
a very small error rate. The spec seems to support that (USB 2.0, section
4.7.4):

# The timely delivery of isochronous data is ensured at the expense of
# potential transient losses in the data stream. In other words, any error
# in electrical transmission is not corrected by hardware mechanisms such
# as retries. In practice, the core bit error rate of the USB is expected
# to be small enough not to be an issue.

Jonathan

 

[Robert Latest]

On 14 Aug 2005 20:12:19 -0700,

Well, I'm sorry if for any reason that our product makes you so upset
(you sounded very upset).

You must be new to Usenet. You haven't heard upset yet, let alone very.

But anyway, I think if you can make a "low
cost" 24 bit DAQ,

Never heard of a DAQ. What is it?

robert

 

[Winfield Hill]

HYTEK wrote...

Well, I'm sorry if for any reason that our product makes you so upset
(you sounded very upset).
Wrong.

But anyway, I think if you can make a "low cost" 24 bit DAQ, it will
be very useful. But just keep in mind (sorry, I really don't intend
to teach anybody here, but I thought this information maybe useful
to some people) ... [ snip ]

Not only are you not going to teach anyone here, I trust they'll
be sure to ignore your "advice" and do their own calculations.

 

[Rene Tschaggelar]

Too_Many_Tools wrote...



Yes. Plus, 32k Samples/Sec is hardly "full speed" is it? Shame.

You're not really expecting a 10MSample ADC for these 49$ ?
Actually, I'd expect two 10Mbit ADC channels including
preamplifier and filters for that money. Plus a megasample
buffer on each channel.


Rene

 

[Mike Harrison]

You're not really expecting a 10MSample ADC for these 49$ ?
Actually, I'd expect two 10Mbit ADC channels including
preamplifier and filters for that money. Plus a megasample
buffer on each channel.


Rene

...and quoting 'USB 2.0 Full speed' is also a little misleading as that is actually no faster than
USB 1.1.
Full speed = 12mbits, High speed = 480mbits.

 

[Joerg]

Hello Irene,

Well, I'm sorry if for any reason that our product makes you so upset
(you sounded very upset). ...

I don't think anybody got upset here in this thread. In others, maybe,
but this newsgroup is fairly decent in tone.

But I think it is good that you participated in a discussion. Most other
companies that want to advertise their product via usenet don't do that,
they just post and nobody ever answers. I appreciate that you didn't
follow that trend and answered. That was nice.

Regards, Joerg

 

[Ian Stirling]

Well, I'm sorry if for any reason that our product makes you so upset
(you sounded very upset). But anyway, I think if you can make a "low
cost" 24 bit DAQ, it will be very useful. But just keep in mind (sorry,
I really don't intend to teach anybody here, but I thought this
information maybe useful to some people)
1. The USB transfer method for audio may not be suitable for a DAQ, you
can find those information in books about USB. That is why you see the
audio (or even video) signal can be transfered a lot faster, but it may
not be suitable to a DAQ. I have explained a little bit in my other
reply.

Which is basically false.
Yes, the transfer may not be as easy.

However, with timestamping and a little protocol in the driver and
sending stacks, you can easily construct a much higher bandwidth
reliable transport, as long as there is enough average bandwidth
available, and a few milliseconds of buffer time.

 

[Too_Many_Tools]

I would agree....to spam and run is extremely poor taste.

My main concern is the misrepresentation of the pricing. To do it
because everyone else is a poor excuse. In marketing, one looks for
ways to stand out in the crowd of competition. In my opinion, being
honest upfront with pricing and specs puts a company on my A list of
prospective suppliers. Something to think about...

TMT

 

[Steve]

I would welcome a 24 bit USB device with 1 or 2 channels for $100 for
chromatorgraphy data collection (say to 10 Hz). Linear Technology No
Latency Delta Sigma ADCs work well for me clocked with digital signals
from a serial or parallel port. They are able to detect the voltage
drop across a one inch length of wire passing a few mA. See their
demo boards/info. I wish someone would add a hardware clock for
reproducible time-between-points, a little local buffer memory and USB
interface (hint-hint Irene). Linear does have a DC590A evaluation kit
that includes a USB interface to these ADCs.

http://www.linear.com/pc/categoryProducts.do



Many low cost SUB devices use a biased resitor divider to obtain a
bipolar input range. Thus they have a relatively high bias current
that changes with input voltage.

LabJACK U12
http://www.labjack.com/labjack_u12.html

Measurement Computing
http://www.measurementcomputing.com/cbicatalog/directory.asp?dept_id=403

USB-1608FS 16 bit $400

USB-1208LS $110
12-bit analog input, 1.2 kS/s

USB-1208FS $150
12-bit resolution, 50 kS/s


National Instruments
NI USB-6008
Eight 12-bit analog input channels, 12 digital I/O lines, 2 analog
outputs, 1 counter
$145
http://www.ni.com/dataacquisition/

 

[Joerg]

Hello Steve,

I would welcome a 24 bit USB device with 1 or 2 channels for $100 for
chromatorgraphy data collection (say to 10 Hz). Linear Technology No
Latency Delta Sigma ADCs work well for me clocked with digital signals
from a serial or parallel port. They are able to detect the voltage
drop across a one inch length of wire passing a few mA. See their
demo boards/info. I wish someone would add a hardware clock for
reproducible time-between-points, a little local buffer memory and USB
interface (hint-hint Irene). Linear does have a DC590A evaluation kit
that includes a USB interface to these ADCs.

With laptops and possibly also with PCs there is a whole other issue:
Noise loops originating from its power supply. When going to 24 bits it
may be necessary to replace that with a quiet linear supply.

Regards, Joerg

 

[Too_Many_Tools]

Thanks for the product listings.

Anyone else?

I am always looking for economical data acquisition offerings.

TMT