# Use impedance to determine if items on a surface have changed?

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- I have a surface and am constantly measuring the impedance

- I placed an object on the surface, any material

Is it possible to use the impedance to detect a change? I'm not interested in the specific weight/mass, just interested if a "change" was triggered?

Take it a step further, would a rise or drop in impedance correlate with objects being added or removed?

Thanks!

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1 hour ago, apeg said:

- I have a surface and am constantly measuring the impedance

- I placed an object on the surface, any material

Is it possible to use the impedance to detect a change? I'm not interested in the specific weight/mass, just interested if a "change" was triggered?

Take it a step further, would a rise or drop in impedance correlate with objects being added or removed?

Thanks!

We would need sufficient information to begin to answer this question.

Impedance ? Acoustic impedance ? Radiation impedance? Electromagnetic impedance ?  Impedance between the surface and something else ?

Yes it may be possible to detect an intervening object depending upon the details ( a lot more of them) . Capacitive coupling comes to mind.

Over to you.

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My goal is to see if I can economically create a large floor covering that would have the ability to detect when an object has been placed or removed from the surface.

The idea originated from a BMI scale that uses electrical impedance to make rough calculations of the person's body composition. The problem there is the contact points are not connected on their own, it's the person who completes the circuit.

I'm curious if there is a way to adapt the idea; if the contact points are connected via the surface material (a sheet of metal) and the impedance is constantly measured will placing or removing an object (of any material) create a change in the measurement, enabling me to trigger a change event, or better yet determine if something was removed or added to the surface.

The only ace up my sleeve is that I don't need to know the weight/mass, only the change even and direction of. Weight/mass would be a great tertiary bonus, but not required.

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6 hours ago, apeg said:

My goal is to see if I can economically create a large floor covering that would have the ability to detect when an object has been placed or removed from the surface.

The idea originated from a BMI scale that uses electrical impedance to make rough calculations of the person's body composition. The problem there is the contact points are not connected on their own, it's the person who completes the circuit.

I'm curious if there is a way to adapt the idea; if the contact points are connected via the surface material (a sheet of metal) and the impedance is constantly measured will placing or removing an object (of any material) create a change in the measurement, enabling me to trigger a change event, or better yet determine if something was removed or added to the surface.

The only ace up my sleeve is that I don't need to know the weight/mass, only the change even and direction of. Weight/mass would be a great tertiary bonus, but not required.

You have not given details the object to be detected, and if it is the only object on the floor.

Perhaps you should investigate graphics tablets,

They can detect the presence or absence of the stylus pen by various different technologies.

But a floor sized version could be quite expensive.

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The object(s) will be rubber, plastic, and cardboard. There will be multiple objects on the surface at a time.

I am assuming a stylus-type solution will be costly, but you have given me a path to investigate. A quick search shows there are a number of different methods of screen touch detection, hopefully, one stands a chance at low-cost scaling.

Thanks!

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Unless you somehow incorporate some computer I do not see how, using my currently limited knowledge, you can detect multiple different objects using a single impedance along. And even with that you would require positional data. Of course I could be wrong. An analogy would be that you can determine 1+2+3+4 = 10, but you can not determine 10 = 1+2+3+4 if you only have 10 as the value. You can only guess at it. And because you are using only a single impedance value then it would be much more difficult to determine positional values. Now this is just a super wrong guess so do not take my word for it, but you could possible...maybe....use Fourier Transform in some manner to derive separate signals. However I know very little about Fourier transform so I cannot say.

Edited by ALine
Needed to correct an error
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there was a typo in my post so I'm gonna make the correction here.

"alone" not "along"

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On 5/14/2021 at 6:54 PM, apeg said:

My goal is to see if I can economically create a large floor covering that would have the ability to detect when an object has been placed or removed from the surface.

The idea originated from a BMI scale that uses electrical impedance to make rough calculations of the person's body composition. The problem there is the contact points are not connected on their own, it's the person who completes the circuit.

I'm curious if there is a way to adapt the idea; if the contact points are connected via the surface material (a sheet of metal) and the impedance is constantly measured will placing or removing an object (of any material) create a change in the measurement, enabling me to trigger a change event, or better yet determine if something was removed or added to the surface.

The only ace up my sleeve is that I don't need to know the weight/mass, only the change even and direction of. Weight/mass would be a great tertiary bonus, but not required.

'Robotic skin' is a highly active area of current research, and your OP seems to require a relatively low resolution, planar version of the same thing.

I'm puzzled why you pick impedance as the sensed property for this. Most work in this field has been focused on traditional resistance strain gauges, piezoresistance, and capacitance methods though Fibre Bragg Gratings (FBGs) seem to have received a lot of attention recently.

The EU Roboskin Project is funded to the tune of about 5 million Euros: details at https://cordis.europa.eu/project/id/231500

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2 hours ago, sethoflagos said:

'Robotic skin' is a highly active area of current research, and your OP seems to require a relatively low resolution, planar version of the same thing.

I'm puzzled why you pick impedance as the sensed property for this. Most work in this field has been focused on traditional resistance strain gauges, piezoresistance, and capacitance methods though Fibre Bragg Gratings (FBGs) seem to have received a lot of attention recently.

The EU Roboskin Project is funded to the tune of about 5 million Euros: details at https://cordis.europa.eu/project/id/231500

All sounds like useful information. +1

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• 1 month later...
On 5/14/2021 at 9:54 AM, apeg said:

My goal is to see if I can economically create a large floor covering that would have the ability to detect when an object has been placed or removed from the surface.

The idea originated from a BMI scale that uses electrical impedance to make rough calculations of the person's body composition. The problem there is the contact points are not connected on their own, it's the person who completes the circuit.

I'm curious if there is a way to adapt the idea; if the contact points are connected via the surface material (a sheet of metal) and the impedance is constantly measured will placing or removing an object (of any material) create a change in the measurement, enabling me to trigger a change event, or better yet determine if something was removed or added to the surface.

The only ace up my sleeve is that I don't need to know the weight/mass, only the change even and direction of. Weight/mass would be a great tertiary bonus, but not required.

I'd be inclined to consider measuring vibrations within the surface material. This strikes me as something that could be done by gathering a lot of test data to create a data model that a computer can use to extract meaningful information.

What are you trying to measure anyway? simply the placement/removal of something from the surface or its location too?

When you say you're measuring impedance can you elaborate?

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