Searching \ for '[EE] resistive force sensing' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=resistive+force
Search entire site for: 'resistive force sensing'.

Exact match. Not showing close matches.
PICList Thread
'[EE] resistive force sensing'
2009\03\23@091745 by alan smith

picon face

Question was brought up, and perhaps someone has an answer.

The problem to solve is to be able to repeatable and reliably measure a weight of a range of 35lbs to 150lbs using some sort of flat & flexible surface.  I've used load cells before but they are too bulky and expensive.  Ideally he wants this to be portable and flexible so some sort of resistive network maybe?  The range can also be divided up...say 35 to 65, 65 to 95, etc...one model does not need to cover the entire range.  Also it does not need to be accurate to the pound..can be +/- 2 to 4 pounds.  The micro would measure the output of the sensor, and do a lookup table or something based on what is coming in.  Its more of a go/no go type application.

Any thoughts?


     

2009\03\23@092856 by Adam Field

flavicon
face
>
> The problem to solve is to be able to repeatable and reliably measure a weight of a range of 35lbs to 150lbs using some sort of flat & flexible surface.  I've used load cells before but they are too bulky and expensive.  Ideally he wants this to be portable and flexible so some sort of resistive network maybe?  The range can also be divided up...say 35 to 65, 65 to 95, etc...one model does not need to cover the entire range.  Also it does not need to be accurate to the pound..can be +/- 2 to 4 pounds.  The micro would measure the output of the sensor, and do a lookup table or something based on what is coming in.  Its more of a go/no go type application.
>

Can you measure the flex of the surface from the bottom? With a laser
or even IR you I would think you could get into that +/- 2 pounds
depending on the "flexible" surface. Most of the robot hobby sites
have write ups on distance measuring with pics and other
microcontrollers.

2009\03\23@094404 by Bob Ammerman

picon face
> The problem to solve is to be able to repeatable and reliably measure a
> weight of a range of 35lbs to 150lbs using some sort of flat & flexible
> surface. I've used load cells before but they are too bulky and expensive.
> Ideally he wants this to be portable and flexible so some sort of
> resistive network maybe? The range can also be divided up...say 35 to 65,
> 65 to 95, etc...one model does not need to cover the entire range. Also it
> does not need to be accurate to the pound..can be +/- 2 to 4 pounds. The
> micro would measure the output of the sensor, and do a lookup table or
> something based on what is coming in. Its more of a go/no go type
> application.

Many years ago one of my customers did some research on using fiber optics
to measure weight. You arrange a piece of fiber so that it is 'bent' when
the weight is applied, then measure the change in transmissivity. I don't
think they ever commercialized the idea, but it might work.

-- Bob Ammerman
RAm Systems

2009\03\23@100937 by John Coppens

flavicon
face
On Mon, 23 Mar 2009 06:17:40 -0700 (PDT)
alan smith <spam_OUTmicro_eng2TakeThisOuTspamyahoo.com> wrote:

> Any thoughts?

Any reason why you are not considering strain gauges? It seems the
logical solucion. Cheap, and the precision is in the order of what you
are looking for. Relatively easy to apply too.

John

2009\03\23@100948 by Gordon Williams

flavicon
face
I've not used these, but may be accurate enough for you.

http://www.tekscan.com/flexiforce.html

Gordon Williams

{Original Message removed}

2009\03\23@101203 by Robert Young

picon face


> Date: Mon, 23 Mar 2009 06:17:40 -0700
> From: .....micro_eng2KILLspamspam@spam@yahoo.com
> Subject: [EE] resistive force sensing
> To: piclistspamKILLspammit.edu
>
>
> Question was brought up, and perhaps someone has an answer.
>
> The problem to solve is to be able to repeatable and reliably measure a weight of a range of 35lbs to 150lbs using some sort of flat & flexible surface.  I've used load cells before but they are too bulky and expensive.  Ideally he wants this to be portable and flexible so some sort of resistive network maybe?  The range can also be divided up...say 35 to 65, 65 to 95, etc...one model does not need to cover the entire range.  Also it does not need to be accurate to the pound..can be +/- 2 to 4 pounds.  The micro would measure the output of the sensor, and do a lookup table or something based on what is coming in.  Its more of a go/no go type application.
>
> Any thoughts?
>

Contact Sensor Products, ask for Jason Blume.

http://www.sensorprod.com/index.php
973.884.1755 (USA, Eastern Standard Time)

Rob

2009\03\23@112353 by Walter Banks

picon face
An anchored beam with a glue on strain gauge sensor. The sensors are very
low cost and can be read with one of the charge balancing circuits
to at least your requirements.

http://www.bytecraft.com/Low_Cost%2C_Low_Speed_A_D_conversion_for_Embedded_Systems

Use Ri as the sensor in the above example. Tie the open end to Vcc. It will be slow a few ms to
read but very low cost

The output is linear, with two point calibration.

Regards,

--
Walter Banks
Byte Craft Limited
http://www.bytecraft.com




alan smith wrote:

> Question was brought up, and perhaps someone has an answer.
>
> The problem to solve is to be able to repeatable and reliably measure a weight of a range of 35lbs to 150lbs using some sort of flat & flexible surface.  I've used load cells before but they are too bulky and expensive.  Ideally he wants this to be portable and flexible so some sort of resistive network maybe?  The range can also be divided up...say 35 to 65, 65 to 95, etc...one model does not need to cover the entire range.  Also it does not need to be accurate to the pound..can be +/- 2 to 4 pounds.  The micro would measure the output of the sensor, and do a lookup table or something based on what is coming in.  Its more of a go/no go type application.
>
> Any thoughts?
>
>
> -

2009\03\23@114349 by Alan B. Pearce

face picon face
>Many years ago one of my customers did some research on using fiber
>optics to measure weight. You arrange a piece of fiber so that it
>is 'bent' when the weight is applied, then measure the change in
>transmissivity. I don't think they ever commercialized the idea,
>but it might work.

I believe the Netherlands railways system uses a similar idea to know how
far down a block of track a train has travelled. I believe the fibre is
attached to the rail somehow, and the weight of the train bends the track
enough that the stresses in the fibre are sufficient for a TDM pulse to
signify how far away the train is with sufficient accuracy to be a useful
measuring tool.

2009\03\23@132510 by alan smith

picon face

Thanks for the suggestions....I will follow up in the next week and see if either might be a solution to this.


--- On Mon, 3/23/09, Walter Banks <.....walterKILLspamspam.....bytecraft.com> wrote:

{Quote hidden}

2009\03\23@142614 by Marc Nicholas

picon face
Someone already posted the FlexiForce sensor link, but if you want to get
one in a hurry and also look at some of the work already being done for you
(eval circuit, sample code):

http://www.parallax.com/Store/Sensors/PressureFlexRPM/tabid/177/CategoryID/52/List/0/Level/a/ProductID/384/Default.aspx?SortField=ProductName%2cProductName

Hope that helps.

-marc

On Mon, Mar 23, 2009 at 9:17 AM, alan smith <@spam@micro_eng2KILLspamspamyahoo.com> wrote:

{Quote hidden}

> -

2009\03\23@155017 by Jinx

face picon face
> I believe the Netherlands railways system uses a similar idea to know
> how far down a block of track a train has travelled. I believe the fibre is
> attached to the rail somehow, and the weight of the train bends the track
> enough that the stresses in the fibre are sufficient for a TDM pulse to
> signify how far away the train is with sufficient accuracy to be a useful
> measuring tool.

I saw a TV item on that (on a Beyond 2000 science program many years
ago). ISTR the method was to compare time travelled, as flexing causes
more bouncing off the walls of the cable. One use of the system was for
automatic and emergency stopping at a terminus. Pistons pushed a brake
rail towards the running rail, clamping the wheel flanges

2009\03\23@160710 by Michael Algernon

flavicon
face
If no one has mentioned it yet...
check out
http://www.sparkfun.com/commerce/product_info.php?products_id=8685

They have 3 varieties of force sensors
MA

2009\03\23@164930 by cdb

flavicon
face
A variation on a theme - the piezo cable that is used in traffic
counting or time lapse speed checking - the rubber looking cable that
is layed across the road. Maybe measure the voltage/frequency returned
by the piezo - I beleive these cables (with unit) can differentiate
between trucks/axles/cars/bikes etc.

Colin
--
cdb, KILLspamcolinKILLspamspambtech-online.co.uk on 24/03/2009

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359






2009\03\23@165519 by Robert Young

picon face




{Quote hidden}

Those are the Tekscan single point sensors, also available from Parallax, Jameco and a few other sources.  The Parallax web page was already referenced.

Rob

2009\03\23@200143 by Michael Algernon

flavicon
face
> Question was brought up, and perhaps someone has an answer.
>
> The problem to solve is to be able to repeatable and reliably  
> measure a weight of a range of 35lbs to 150lbs using some sort of  
> flat & flexible surface.  I've used load cells before but they are  
> too bulky and expensive.  Ideally he wants this to be portable and  
> flexible so some sort of resistive network maybe?  The range can  
> also be divided up...say 35 to 65, 65 to 95, etc...one model does  
> not need to cover the entire range.  Also it does not need to be  
> accurate to the pound..can be +/- 2 to 4 pounds.  The micro would  
> measure the output of the sensor, and do a lookup table or something  
> based on what is coming in.  Its more of a go/no go type application.
>
> Any thoughts?
>

Apply the force to a metal strip that will flex with respect to  
another conductor.
measure the change in capacitance.
There are a gazillion ways to measure capacitance.  There are ICs that  
measure capacitance.
       www.discovercircuits.com/S/s-capacitance.htm
       http://www.analog.com/en/analog-to-digital-converters/capacitance-to-digital-converters/ad7150/products/product.html

2009\03\23@221625 by Jake Anderson

flavicon
face
cdb wrote:
> A variation on a theme - the piezo cable that is used in traffic
> counting or time lapse speed checking - the rubber looking cable that
> is layed across the road. Maybe measure the voltage/frequency returned
> by the piezo - I beleive these cables (with unit) can differentiate
> between trucks/axles/cars/bikes etc.
>  
I'm pretty sure that the ones they stick over the road actually work on
air pressure, IE they are a hose rather than an expensive piezo bit.
I believe that they do use piezo for speed cameras that are buried in
the road.

2009\03\23@223323 by cdb

flavicon
face


:: I'm pretty sure that the ones they stick over the road actually
:: work on
:: air pressure, IE they are a hose rather than an expensive piezo
:: bit.
:: I believe that they do use piezo for speed cameras that are buried
:: in
:: the road.

Maybe there are two types of sensors. I've never taken one apart, just
recall an article in the UK about them along with an offer of 1000'
drum of the stuff for GBP25.00 - this was back in the early 90's so
don't all rush to find some.

Here is a link to a modern day supplier - they've got some interesting
stuff to play around with, including pressure sensing.

http://www.meas-spec.com/product/t_product.aspx?id=2476

Colin
--
cdb, TakeThisOuTcolinEraseMEspamspam_OUTbtech-online.co.uk on 24/03/2009

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359







2009\03\23@232442 by Tony Smith

flavicon
face
> > A variation on a theme - the piezo cable that is used in traffic
> > counting or time lapse speed checking - the rubber looking cable that
> > is layed across the road. Maybe measure the voltage/frequency returned
> > by the piezo - I beleive these cables (with unit) can differentiate
> > between trucks/axles/cars/bikes etc.
> >
> I'm pretty sure that the ones they stick over the road actually work on
> air pressure, IE they are a hose rather than an expensive piezo bit.
> I believe that they do use piezo for speed cameras that are buried in
> the road.


All the ones I've seem work on air pressure.  Simple, cheap, works, what
more do you want?

Road sensors are current loops, the presence of enough steel over them
alters the current flow, unless you ride a motorcycle.  (As a bonus, you can
ride between or beside them and not trip the sensor...)

Tony

2009\03\24@075026 by olin piclist

face picon face
Jake Anderson wrote:
> I'm pretty sure that the ones they stick over the road actually work on
> air pressure, IE they are a hose rather than an expensive piezo bit.

The ones I have seen work that way.  There may be different techniques for
sensing the air pressure change, but the part that goes on the road is just
a rubber hose.

> I believe that they do use piezo for speed cameras that are buried in
> the road.

The permanent in-road sensors I've seen have all been large loops of wire,
about a meter or two accross (they tend to be elongated in the direction of
travel).


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\03\24@094945 by eross

flavicon
face
Tony Smith wrote:
{Quote hidden}

The circuits I have seen, and documentation I've read on the vehicle
sensors have used the the loops as inductors in an oscillator. The
vehicle changes the inductance and thus the frequency. The change in
frequency is smaller for cycles and inside the chosen 'ignore' band of
the sensor.

2009\03\24@101048 by Mark E. Skeels

flavicon
face
Coming in on this thread late, but around here last year they placed
temporary "sensors" on the roads everywhere. there were approx 4"x4"
flat (maybe 1/2" tall??) units stuck down to the center of the lanes
with what looked like big pieces of rubber adhesive tape.

After a week or so, they came around and removed them all, leaving the
square outline in each piece of "tape" where they were cut out.

I googled looking for these devices but found nothing; I wonder if
anybody has any idea what they were and how they worked.....I'm sure
they were self contained devices with a power source and a uC to log
vehicle traffic.....

Mark Skeels
Engineer
Competition Electronics, Inc.
TEL: 815-874-8001
FAX: 815-874-8181
http://www.competitionelectronics.com


Olin Lathrop wrote:
{Quote hidden}

More... (looser matching)
- Last day of these posts
- In 2009 , 2010 only
- Today
- New search...