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From: MoiInAust on 4 Dec 2009 16:04

"Jim Mack" <no-uce-ube(a)mdxi.com> wrote in message
news:LeKdnVDz6YCZ8oTWnZ2dnUVZ_gSdnZ2d(a)giganews.com...
> MoiInAust wrote:
>>>
>>> http://www.lvr.com/usb.htm
>>>
>> Thanks for that, but I found it too lengthy and confusing.
>>
>> I am trying to develop an application that reads voltages via the
>> USB port and presents them in a graph. Both the x and y will be
>> associated with voltage changes (ie time will not come into it).
>> There will be no actual HID devices to identify and I don't want an
>> all singing and dancing general application that will eg check
>> which device is there. I don't want someone to write the code. I am
>> happy to sytruggle through that. But I do want to know the syntax
>> just to read voltages via the USB port. Like 'vbReadUSB' or
>> suchlike.
>
>
> What you're asking for doesn't exist. The USB port is a serial digital
> port. It does not respond to analog voltage levels. That would require
> an ADC.
>
> You can buy ADCs that have a USB interface, which would come with a
> driver and perhaps a software library / ActiveX. But there is no way
> you will ever read varying analog voltages using the USB port alone.
>
> --
> Jim Mack
> Twisted tees at http://www.cafepress.com/2050inc
> "We sew confusion"

THat's OK. I'm quite happy about an ADC, but how then to read the output
through the USB port into a vb prgram?


From: MoiInAust on 4 Dec 2009 16:08

"Schmidt" <sss(a)online.de> wrote in message
news:%23sGipESdKHA.1652(a)TK2MSFTNGP05.phx.gbl...
>
> "MoiInAust" <user(a)user.com> schrieb im Newsbeitrag
> news:4b196958$1(a)dnews.tpgi.com.au...> > Main page:
>
>
>> I do want to know the syntax just to read voltages
>> via the USB port. Like 'vbReadUSB' or suchlike.
>
> The "syntax" is defined by the vendor of your USB-
> AD-converter-Box.
>
> These usually come with a full set of drivers/APIs (for all
> kind of languages) - in most cases even with VB5/6
> sample-code (and an "USBDeviceAPI.bas" file, which
> contains the appropriate Declares.
>
> Here are some vendors, which I know, deliver
> VB-modules with their boxes:
>
> http://www.meilhaus.de/en/home/
> (they distribute the LabJack-Boxes here, which you can
> directly buy at: http://labjack.com/ too of course.
>
>
> http://www.datatranslation.com/
> (not the cheapest, but they offer true-parallel-AD-sampling
> boxes in good quality - one of the not that costly ones
> is the DT9810)
>
> Don't know, what you have in mind exactly - if it needs to
> be even smaller (in the 20$-range), in the last years nearly
> each of the larger chip-vendors (Texas Instruments, Analog
> Devices, etc.) has brought up nice "thumb-size" evaluation-
> kits - usually involving a micro-processor with integrated
> A/D-ports, Rs232, etc. - the PC-communication is then
> done mostly over a virtual Rs232-port, which you could
> read and write with the VB-COMM-control.
> Here's an example-picture of that category.
> http://focus.ti.com/graphics/tool/ez430-f2013.jpg
>
> The datarate (the capture-frequency) - as well as the bit-depth
> is not that high as with the "real measurement-boxes" above,
> (which don't emulate a COM-port, but talk over their own
> USB-drivers-API) but for many scenarios these small "sticks"
> are good enough.
>
> Olaf
>
>
These are great clues. Thanks for the replies Guys. What I am hoping to make
is a vb6 wobbulator. A swept RF signal passes over the bandwidth of an IF
and displays a graph of frequency versus amplitude. Gives the classic IF
characteristic. I can do this on an analogue scope but would like to do it
on a full sized flat screen and maybe display a graticule of frequency and
dBs too.


From: Schmidt on 4 Dec 2009 18:20

"MoiInAust" <user(a)user.com> schrieb im Newsbeitrag
news:4b197a59(a)dnews.tpgi.com.au...

> These are great clues. Thanks for the replies Guys.
> What I am hoping to make is a vb6 wobbulator. A
> swept RF signal passes over the bandwidth of an IF
> and displays a graph of frequency versus amplitude.
> Gives the classic IF characteristic. I can do this on an
> analogue scope but would like to do it on a full sized
> flat screen and maybe display a graticule of frequency and
> dBs too.

Hmm, in what frequency-ranges do you want to get
that to work?
If you really mean radio-frequencies, then even the
more expensive USB-A/D-boxes are not able to
"keep pace" with such an requirement.

About 1-2MegaSamples per second is the maximum IMO
for "normal" AD-digitizing over USB - and radio-
frequencies are much higher than even that.

If you only want to do that in the "near NF"-range
(below 50kHz) "just for fun", then you can also use your
already built-in soundcard for that (on two channels with
16Bit each, up to a sample-rate of 48kHz).

For radio-frequency-capturing you need special hardware,
which has appropriate fast buffers built in, usually you're
capturing then only "certain, short events" which you can
adjust some "react to" triggers for in the RF/HF-hardware,
so that the internal buffers of the hardware (which can
only store captured HF-samples up to a certain amount ...
speaking: *time*), do not overflow.
Later on with your PC-based software, you typically only
read out the buffered content of such a "trigger-initiated and
captured timeframe" for your "RF-event of interest".

Olaf



From: MoiInAust on 5 Dec 2009 04:58

"Schmidt" <sss(a)online.de> wrote in message
news:%23EFt9mTdKHA.2164(a)TK2MSFTNGP02.phx.gbl...
>
> "MoiInAust" <user(a)user.com> schrieb im Newsbeitrag
> news:4b197a59(a)dnews.tpgi.com.au...
>
>> These are great clues. Thanks for the replies Guys.
>> What I am hoping to make is a vb6 wobbulator. A
>> swept RF signal passes over the bandwidth of an IF
>> and displays a graph of frequency versus amplitude.
>> Gives the classic IF characteristic. I can do this on an
>> analogue scope but would like to do it on a full sized
>> flat screen and maybe display a graticule of frequency and
>> dBs too.
>
> Hmm, in what frequency-ranges do you want to get
> that to work?
> If you really mean radio-frequencies, then even the
> more expensive USB-A/D-boxes are not able to
> "keep pace" with such an requirement.
>
> About 1-2MegaSamples per second is the maximum IMO
> for "normal" AD-digitizing over USB - and radio-
> frequencies are much higher than even that.
>
> If you only want to do that in the "near NF"-range
> (below 50kHz) "just for fun", then you can also use your
> already built-in soundcard for that (on two channels with
> 16Bit each, up to a sample-rate of 48kHz).
>
> For radio-frequency-capturing you need special hardware,
> which has appropriate fast buffers built in, usually you're
> capturing then only "certain, short events" which you can
> adjust some "react to" triggers for in the RF/HF-hardware,
> so that the internal buffers of the hardware (which can
> only store captured HF-samples up to a certain amount ...
> speaking: *time*), do not overflow.
> Later on with your PC-based software, you typically only
> read out the buffered content of such a "trigger-initiated and
> captured timeframe" for your "RF-event of interest".
>
> Olaf
>
>
Thanks Olaf. I wanted to read 455 KHz +- 10 KHz so it sounds like no go.


From: Schmidt on 5 Dec 2009 07:45

"MoiInAust" <user(a)user.com> schrieb im Newsbeitrag
news:4b1a2eba$1(a)dnews.tpgi.com.au...

> > About 1-2MegaSamples per second is the maximum IMO
> > for "normal" AD-digitizing over USB - and radio-
> > frequencies are much higher than even that.
> ...
> ...
> I wanted to read 455 KHz +- 10 KHz so it sounds like no go.
Given my above statement, if you use for example this device-category:
http://www.datatranslation.com/products/dataacquisition/usb/dt9832.asp

Then you can capture a 455kHz signal at a constant rate of
e.g. 2MSample/second (in 16Bit res.) - continously, since
these expensive boxes stream their data over the fast USB2.0
channel.

There are also cheaper USB-based "oscilloscopes" available,
which can work up to 50MHz - but the data from these
devices cannot be transferred continously to your PC-
software anymore - instead these "oszis" buffer shorter
time-intervals of the internally high-frequently captured data -
starting at a trigger-event - and what you get transferred
to your PC (continously) are only the contents of these
shorter time-frames.

Just google around a bit - there are also "specialized forums"
available, where hardware- (or electronics-) related questions
are better placed.

Olaf


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