Re: Display Changes in Resistance caused by stretching a conductive material.

On Thu, 5 Apr 2012 08:12:03 -0700 (PDT), gilak <(E-Mail Removed)>
wrote:

>I wonder whether someone could please help me in devising or buying a
>system for displaying changes in resistance caused by stretching a
>conductive material. I have got the material and able to measure the
>changes in resistance using an ohm meter. I am a computer programmer
>but know nothing about electronics. Ideally I want to be able to read
>data via USB port and then develop my own program to display the
>changes. Any help on this will be appreciated.

The simplest way to start would be to use a USB data logger. Connect the
conductive material and one other resistor in a "voltage divider"
configuration, and measure the voltage from the junction between the
two, referenced to ground. Then do the math to work backwards to the
resistance.

<http://www.mccdaq.com/usb-data-acquisition/USB-1208-Series.aspx> is one
option. It includes a basic data logging application as well as the
necessary DLLs for you to write a more sophisticated app, if desired.
The presence of (controllable) analog outs as well as a 5V output would
make your project pretty easy, requiring just this pod plus a resistor
and a little software.

http://www.dataq.com/usb-data-acquis...quisition.html is
another popular source. I don't think they're as flexible as the MCC
pods but they are an option.

--
Rich Webb Norfolk, VA

gilak wrote:

> On Apr 5, 5:58 pm, Tim Wescott <t...@seemywebsite.com> wrote:
>
>>On Thu, 05 Apr 2012 11:33:37 -0400, Rich Webb wrote:
>>
>>>On Thu, 5 Apr 2012 08:12:03 -0700 (PDT), gilak <bkas...@gmail.com>
>>>wrote:
>>
>>>>I wonder whether someone could please help me in devising or buying a
>>>>system for displaying changes in resistance caused by stretching a
>>>>conductive material. I have got the material and able to measure the
>>>>changes in resistance using an ohm meter. I am a computer programmer but
>>>>know nothing about electronics. Ideally I want to be able to read data
>>>>via USB port and then develop my own program to display the changes. Any
>>>>help on this will be appreciated.
>>
>>>The simplest way to start would be to use a USB data logger. Connect the
>>>conductive material and one other resistor in a "voltage divider"
>>>configuration, and measure the voltage from the junction between the
>>>two, referenced to ground. Then do the math to work backwards to the
>>>resistance.
>>
>>><http://www.mccdaq.com/usb-data-acquisition/USB-1208-Series.aspx> is one
>>>option. It includes a basic data logging application as well as the
>>>necessary DLLs for you to write a more sophisticated app, if desired.
>>>The presence of (controllable) analog outs as well as a 5V output would
>>>make your project pretty easy, requiring just this pod plus a resistor
>>>and a little software.
>>
>>>http://www.dataq.com/usb-data-acquis...isition.htmlis
>>>another popular source. I don't think they're as flexible as the MCC
>>>pods but they are an option.
>>
>>Gilak, how much sensitivity do you need? Is this a hobby or school
>>project? A production device? What sort of production volumes are you
>>dealing with? Who's going to be building it? Do you have a target price
>>for the end system?
>>
>>Rich's idea is a good one, but you'll have a little bit of signal buried
>>in a whole lot of noise.
>>
>>Assuming that it's precise enough, the very easiest way to do this would
>>be to get a digital multimeter with USB output and read the resistance of
>>your wire directly. I'd be kind of surprised if you couldn't buy a
>>suitable (again, assuming sufficient accuracy) from Radio Shack for less
>>than $30. If you need this for a product, then go looking for USB DAQ
>>modules that'll measure resistance accurately.
>>
>>If a cost-effective DMM isn't going to be precise enough, then your best
>>bet is probably to use a bridge and amplifier, although running a known
>>current through the wire and measuring its voltage drop with a really
>>accurate ADC has its merits (and complications). Let us know the details
>>of what sort of project this is, and we can help you better.
>>
>>--
>>My liberal friends think I'm a conservative kook.
>>My conservative friends think I'm a liberal kook.
>>Why am I not happy that they have found common ground?
>>
>>Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
>
>
> A big thank you to Rand, Rich and Tim for their prompt replies.
>
> Randy: I would like to start with a pre-built test instrument and then
> progress to devising a bespoke system. The system will eventually be
> used in a patient monitoring environment and needs to be packaged in
> a form that is easy to operate and maintain. I think I could probably
> afford a hand-held oscilloscope with DVM functions and USB
> connectivity.
>
> Rich: Excellent advise. I had a look at USB-1208 Series data loggers
> specification. I am hoping it will give me the flexibility in design
> and user presentation that I need..
>
> Tim: It will be a one-of-prototype for use in a health care
> environment. This is a proof of concept research project and if
> successful we will approach a manufacturer for a production model. I
> didn’t know you could buy digital multimeter with USB connectivity.
> If I could read the output direct from a multimeter then it would be a
> good start in demonstrating the concept behind the project.

Look on line for FLuke DMM's, Most of the upper models have a serial
connection option. This will allow you to monitor exactly what the DMM
is monitoring..

A 189/289 is good for this.

P.S.

You didn't specify as to how low of R you are measuring? That is
important.

Jamie