Analog To USB

O

OldGuy

Guest
Looking for a simple and inexpensive analog to USB hw module with sw
drivers that I can code into. One or two channels. any input range.
12 bits or more. a kit would be OK. do not want to do a PWB myself.
PC Win XP or 7.



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
Ahh yes. I spend other peole's money alot faster as well...

How much bandwidth you need ? Maybe one of the cheap USB scopes would work. I think I saw some that were two channels.

Looks like those Labjacks are like eight channels and more. Looked like the one was around a hundred bucks. For eight channels that doens't seem so bad but I see that if you do not need it, why pay for it ?

Or, maybe there are used ones on eBay ?
 
On 5/12/2014 7:37 PM, OldGuy wrote:
Looking for a simple and inexpensive analog to USB hw module with sw
drivers that I can code into. One or two channels. any input range. 12
bits or more. a kit would be OK. do not want to do a PWB myself. PC
Win XP or 7.
Click to expand...

I'm a fan of LabJacks for that.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
I have used those when my company paid but I asked for inexpensive
since I am paying.



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On 5/12/2014 8:08 PM, OldGuy wrote:
I have used those when my company paid but I asked for inexpensive since
I am paying.



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Click to expand...

They come down to about $75. What do you mean by "inexpensive"?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
In article <lkrlv8$23lu$1@adenine.netfront.net>, OldGuy@nospam.com
says...
Looking for a simple and inexpensive analog to USB hw module with sw
drivers that I can code into. One or two channels. any input range.
12 bits or more. a kit would be OK. do not want to do a PWB myself.
PC Win XP or 7.



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Click to expand...

Get a USB sound dongle and remove the DC blocking caps? With that,
you can use the windows standard media API's
or that for 42 bucks.

http://www.ebay.com/itm/Home-Automation-USB-DAQ-28-GPIO-8-ADC-4-DAC-4-
PWM-UART-/110633398856

Jamie
 
On Mon, 12 May 2014 21:15:49 -0400, "Maynard A. Philbrook
Jr." <jamie_ka1lpa@charter.net> wrote:

In article <lkrlv8$23lu$1@adenine.netfront.net>, OldGuy@nospam.com
says...

Looking for a simple and inexpensive analog to USB hw module with sw
drivers that I can code into. One or two channels. any input range.
12 bits or more. a kit would be OK. do not want to do a PWB myself.
PC Win XP or 7.



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

Get a USB sound dongle and remove the DC blocking caps? With that,
you can use the windows standard media API's
or that for 42 bucks.

http://www.ebay.com/itm/Home-Automation-USB-DAQ-28-GPIO-8-ADC-4-DAC-4-
PWM-UART-/110633398856
Click to expand...

I have had good results with the HDE 5.1 USB device (about
$15 on Amazon), though I used an additional diff-amp circuit
on the input: <http://www.daqarta.com/dw_ggnn.htm>. The
units use a CM6206 chip and have a nice metal case with
room inside for a tiny PC board to hold the diff-amp.
(There are other identical-looking devices that apparently
don't have the same internal layout.)

If you don't use a diff-amp, just bypass the caps, the
digital output would be 'unipolar' with bipolar encoding:
zero input would be reported as negative full-scale,
more-positive inputs would be reported as less-negative, up
through zero to positive full-scale.

The link includes schematics and photos for this device,
but you can probably do the same basic diff-amp mod to most
USB sound devices. You just have to figure out what ADC chip
they use and find its Vref pin to use as the diff-amp ref.
Then you just trace the input channels to find the input
caps and remove them, and connect your diff-amp between the
former cap holes.

You can use the same diff-amp circuit, which includes a link
to a PCB layout you can print off, and one you can send out
to have made by PCB Express.

As for the underlying pre-mod performance of this device,
full measurements of this and several other USB devices are
here:
<http://www.daqarta.com/dw_gguu.htm>

Best regards,


Bob Masta

DAQARTA v7.50
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!
 
On Wed, 14 May 2014 22:22:05 -0700 (PDT), jurb6006@gmail.com
wrote:

Why not just use a common drain JFET, or, if you have enough headroom in the supply, a simple Zener with a bypass and a pullup ?

If you need alot of accuracy, something off the shelf would be better, even though it is more money.
Click to expand...

Not sure what you have in mind. The need is to take
(typically) +/-2.5V signals from the external world and
convert to 0-5V DC for the ADC, with the external ground
referenced to Vref of the ADC. The diff-amp circuit uses a
9V battery as the negative supply. It's auto-switched by
the presence of the +5 USB power.

(Actually, the ADC chips I've seen use 3V or 3.3V supplies,
cut down from the 5V USB, with Vref in the 1.2-1.5V range.)

Best regards,


Bob Masta

DAQARTA v7.50
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!
 
If you take an N channel JFET and put positive DC on the drain and zero volts (quiescent) on the gate, there will be a positive voltage on the source. Not like a MOSFET, it can shift the DC lavel this way in the "source follwer" configuration, a term I do not like to use because it is not right. Nothing follows the source, the source follows the gate.

Actually JFETs are a bit hard to get compared to other devices. they are available but if you go to Digikey and compare how many types they have versus other kinds of transsistors, there aren't that many. Many of them are used for switching because of some other charsacteristics, but not all.

you just put the gate at zero volts with a resistor, put the drain to +5, and pick a resistor that gives you the right voltage at the source. Of course you have to keep the current and therefore the dissipation within limits but I see no problem with that. If the output impedance is too high you can use an "emitter follower" after it, but I really doubt that'll be necessary.

I don't claim this will be totally accurate. The deal with the OP AMPs is probably more suited for instrumentation purposes, but the OP wants cheap and we don't really know the app at the moment. Actually, with a couple of more components ant drift can be compensated. A simple current csource from source to ground could be regulated to keep the voltage shift constant with temperature. I oculd probavbly draw someting up, but later because I am outta here in a few, got some things to do. It really is simple, what I have in mind anyway. The worst it would be is a JFET, a bipolar and a few resistors.
 
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