What is it about conductors that gives them resistive properties?

[jasonbe]

Jason your assumptions don't make sense. Think of a resistor (as 3VO suggested) as a one dimentional device a number from 0 to infinity. If there was a simple practical solution I'm sure it would have been mentioned by now.

I may not be sure of what a resistor is. Would you explain it to me?

 

[jasonbe]

The CCD camera as stated before mounted above the playfield has my vote.

Mine too. But then I would have to connect the camera to a pattern recognition system in order to locate the positions of the pieces, and this is a little too advanced for me now.

 

[dknguyen]

I think it's pretty obvious now we had two different thoughts about how to go about things, so I'll start with yours since in theory it would work, save for some practical limitations.

If I had such a material – assuming that you’re talking about a type of material that can measure distances as a function of electrical resistance, then I might be able to determine more than one piece’s location by first identifying three imaginary points on the material. I believe that it is then possible to identify the location of any point on the game board - occupied by one of these pieces, as a function of diameters of three imaginary circles defined as having a center coincident with these three points - by considering a point where the circumferences of the three imaginary circles intercept.

Are you saying you want to turn one piece (and only one piece at any one time) into an electrode and send a current through it and measure the current arriving each of the 3 contacts?

I can see how that might work in theory, but in practicality you are going to need wires coming off of every playing piece. YOu still have to line the edge of the board with contacts so this method is no simpler than a grid method. It is probably more complicated since you now need to monitor 3 contacts with 3 very sensitive current monitors, as well as driving the current with an accurate driver (as opposed to monitoring 2 contacts with simple go/no go comparators.)

Also remember you can only inject current through one piece at any one time, or else you won't be able to differentiate between the positions of the various pieces.

You also need (fancy) math to map out the circles as well as to find the intersection. You also need math to account for how materials and measurements are never perfect so you will never get a single intersection between the 3 circles. It is much more likely that you will get 3 intersections between each pair of the three circles. These 3 points would form a triangle, somewhere within would be your playing piece, and you would need math to approximate where the best location in that area is (probably the center of the triangle, but that still takes some fairly fancy math to do).

BTW there are two ways to do that, you could use a current source and inject a known current into the board through the playing piece and measure how much current is exiting the board through each of the 3 contacts and compare that to the original amount injected. Or you could use a voltage source and measure the current exiting the board through each of the 3 contacts and then calculate the effective resistance between the playing piece and each contact. Both have the problem of non-linearity because...(see next answer)

If I’m correct, a Gaussian distribution is continuous. However, if I understand what you mean by array correctly, then such a design would not produce an electric output – indicative of the location of a game piece, that could be measured as having a continuous change. What type of circuit would allow me to work with a measurement of change in electricity that is continuous - and could therefore allow me to measure the location of game pieces continuously?

Hypothetically, if you implenented your design you shouldn't bother with look-up tables. If your board was infinite in size you could use a single "simple" current distribution model. But it isn't. Your board is finite sized and the current will distribute differently if the current is injected into the board near the edge than if it is injected near the center. The result is that the effective resistance (if a voltage source is used to inject current into the board through the playing piece) or current at the edge contact (if a current source is used to inject current into the board through the playing piece) that is measured is non-linear with respect to the distance between contact and playing piece.

So you would have to use many different simple models for each area of the board and evaluate them all every time you get a reading or you would have to use one big complicated model. And then you would still have to follow up on the circle intersection math. Either way, this stuff is best left to MATLAB and to do it in real time requires lots of resources and time. It's much easier to map out a grid of points on the board and then place inject current into the board at every point and record the readings at the edge contacts, then put it into a look-up table. If the matrix is fine enough, then you can probably ignore the difference in current distribution effects between two adjacent points and just use interpolation to figure out where a piece is with more resolution than the matrix of test points (ie. if it's sitting between points rather than on a point). Still a lot of math and memory resources.

What is capacitive touch?

It's what is used on touch screens or laptop touchpads (or other things like that).
==================

Now if you wanted still want to talk about how my method worked (and I clearly explained why it does not). It's concept in one dimension is just if you have a long strip of resistive material (ie. a 1D board so to speak) and place a smaller resistive piece of material on it (ie. the playing piece) this would almost be like connecting two resistors in parallel or in series and would thus modify the resistance seen between the two contacts of the larger resistor. In 1D you can only tell if a playing piece is there or not, in 2D you would be able to tell where a piece was on the resistor.

But this is where I start with the problem of current distributing evenly throughout the smaller resistor due to surface contact and volume because of it's distance away from the sight-line between the two contacts of the larger resistor. THen there is the parallel resistance dominance effect made between the small resistor and the path of large resistor that it is in contact with (which acts like a parallel resistance connection), as well as the series resistance dominance effect (which is formed by the aformentioned parallel connection effectively being in series with the remainder of the larger resistor that is not in contact with the small resistor).

THe reason I though this was the only method was because I figured you wanted simple playing pieces with no wires or power sources in them. Either way, this method is not workable with more than one piece, and is barely workable in theory with just one piece.

 

[dknguyen]

Mine too. But then I would have to connect the camera to a pattern recognition system in order to locate the positions of the pieces, and this is a little too advanced for me now.

Is it? Your original scheme had playing pieces that required engineering. What if you just made playing pieces with a small battery inside an an IR LED? And then used a camera with a filter? You end up with a pixel array with bright spots and dark spots. "Just" scan through it and record all the bright spots. Maybe some filtering too to turn the round fuzzy bright spots into a single point, but you get the idea.

As far as image processing goes, it's very lax in requirements. You don't need to compare the current frame to a previous frame so you don't need to hold entire images in memory. It's also sequential scrolling through the pixels checking each one at a time for bright/dark, and after you're done with the bit you never look at it again. In the end you just have a as many numbers as their are playing pieces, each indicating the position of the bright spots.

THe only caveat is all this implies one pixel is bright per piece and some filtering beforehand is needed to get around that which might involve holding more than one pixel's worth of data in memory which could end up being a problem. One way around this is to just skip X pixels every row and skip every Y columns of pixels. You aren't filtering so much as just reducing the resolution of the image. It would be more sensitive to "false" bright spots though, but you could always filter the recorded bright spots over time (which takes much less memory and processing) rather than filtering the image pixels spatially.

Instead of building a complicated board, you are just have a bunch of circuits that have an LED, resistor, battery, and regulator (the playing piece) which is dead easy. And the rest is connecting a camera and microcontroller with the bulk of your work being in firmware. You'd want to find the "right" camera. One that is low resolution that you can put a IR filter onto and has a simple output. The best option is the CMU Cam 3 or the POB Bot camera (you might not even need to use your own MCU for image processing since these have processors on them that you can write firmware for. They also tend to have extra memory on them so you can hold maybe an image in memory to work with rather than just pixel by pixel).

 

[jasonbe]

I think it's pretty obvious now we had two different thoughts about how to go about things, so I'll start with yours since in theory it would work, save for some practical limitations.



Are you saying you want to turn one piece (and only one piece at any one time) into an electrode and send a current through it and measure the current arriving each of the 3 contacts?

I can see how that might work in theory, but in practicality you are going to need wires coming off of every playing piece. YOu still have to line the edge of the board with contacts so this method is no simpler than a grid method. It is probably more complicated since you now need to monitor 3 contacts with 3 very sensitive current monitors, as well as driving the current with an accurate driver (as opposed to monitoring 2 contacts with simple go/no go comparators.)

Also remember you can only inject current through one piece at any one time, or else you won't be able to differentiate between the positions of the various pieces.

You also need (fancy) math to map out the circles as well as to find the intersection. You also need math to account for how materials and measurements are never perfect so you will never get a single intersection between the 3 circles. It is much more likely that you will get 3 intersections between each pair of the three circles. These 3 points would form a triangle, somewhere within would be your playing piece, and you would need math to approximate where the best location in that area is (probably the center of the triangle, but that still takes some fairly fancy math to do).

BTW there are two ways to do that, you could use a current source and inject a known current into the board through the playing piece and measure how much current is exiting the board through each of the 3 contacts and compare that to the original amount injected. Or you could use a voltage source and measure the current exiting the board through each of the 3 contacts and then calculate the effective resistance between the playing piece and each contact. Both have the problem of non-linearity because...(see next answer)


Hypothetically, if you implenented your design you shouldn't bother with look-up tables. If your board was infinite in size you could use a single "simple" current distribution model. But it isn't. Your board is finite sized and the current will distribute differently if the current is injected into the board near the edge than if it is injected near the center. The result is that the effective resistance (if a voltage source is used to inject current into the board through the playing piece) or current at the edge contact (if a current source is used to inject current into the board through the playing piece) that is measured is non-linear with respect to the distance between contact and playing piece.

So you would have to use many different simple models for each area of the board and evaluate them all every time you get a reading or you would have to use one big complicated model. And then you would still have to follow up on the circle intersection math. Either way, this stuff is best left to MATLAB and to do it in real time requires lots of resources and time. It's much easier to map out a grid of points on the board and then place inject current into the board at every point and record the readings at the edge contacts, then put it into a look-up table. If the matrix is fine enough, then you can probably ignore the difference in current distribution effects between two adjacent points and just use interpolation to figure out where a piece is with more resolution than the matrix of test points (ie. if it's sitting between points rather than on a point). Still a lot of math and memory resources.


It's what is used on touch screens or laptop touchpads (or other things like that).
==================

Now if you wanted still want to talk about how my method worked (and I clearly explained why it does not). It's concept in one dimension is just if you have a long strip of resistive material (ie. a 1D board so to speak) and place a smaller resistive piece of material on it (ie. the playing piece) this would almost be like connecting two resistors in parallel or in series and would thus modify the resistance seen between the two contacts of the larger resistor. In 1D you can only tell if a playing piece is there or not, in 2D you would be able to tell where a piece was on the resistor.

But this is where I start with the problem of current distributing evenly throughout the smaller resistor due to surface contact and volume because of it's distance away from the sight-line between the two contacts of the larger resistor. THen there is the parallel resistance dominance effect made between the small resistor and the path of large resistor that it is in contact with (which acts like a parallel resistance connection), as well as the series resistance dominance effect (which is formed by the aformentioned parallel connection effectively being in series with the remainder of the larger resistor that is not in contact with the small resistor).

THe reason I though this was the only method was because I figured you wanted simple playing pieces with no wires or power sources in them. Either way, this method is not workable with more than one piece, and is barely workable in theory with just one piece.

What type of 1D board were you talking about? Do you know where I can get such a long strip of resistive material?... I understand what you mean by saying that the math associated with some of the designs that I have mentioned so far could get very complicated, but I could also calibrate the game board according to electrical readings associated with locations on the game board after these readings were taken.

 

[jasonbe]

A rubber or PVC ESD workbench mat is probably your best option.

Were you recommending something with a surface that had specific resistive properties? I couldn’t find anything like this on the web.

 

[dknguyen]

What type of 1D board were you talking about? Do you know where I can get such a long strip of resistive material?... I understand what you mean by saying that the math associated with some of the designs that I have mentioned so far could get very complicated, but I could also calibrate the game board according to electrical readings associated with locations on the game board after these readings were taken.

1D was just conceptual to help explain things.

 

[jasonbe]

1D was just conceptual to help explain things.

Thanks for your help simplifying the pattern recognition system in your earlier post. Programming such a system sounds very exciting and is something that I would like to do someday. However, I would like to keep this game as compact, lightweight, and portable as possible. It is going to be enough to have to carry around a laptop – without a camera, to make this game operational.

You said earlier that you didn’t think that two dimensional slabs with useful resistive properties were readily available. Do you know where I can find any one dimensional long strips of resistive materials?

 

[jasonbe]

If I go with the grid option, can anyone think of any problems with setting the resistance of each parallel wire in each direction with multiple wires running off of multiple locations on the coil of one of the two large variable resistors that I would have to use with this design? If you have any new ideas, please don’t hesitate to post them - because I am not conclusive about using the grid design.

 

[jasonbe]

Also, can anyone think of any three dimensional models of the flow of electricity in heterogeneous conductors?

 

[blueroomelectronics]

Any chance you'll tell us what the game is?

 

[jasonbe]

Any chance you'll tell us what the game is?

I’d like for the game to help people identify relationships between processes that involve changing spatial relationships between the game pieces and at least three common changing quantitative characteristics of the game pieces that can be initially set to be equal or different. I’d also like for the game to be able to be used as a peripheral to help programmers define mathematical relationships that could exist between the game pieces – in addition to helping people identify these relationships who are not familiar enough with mathematical expressions to program the game pieces. Finally, I’d like for the game to be an oversimplified example of an information source that modeled population dynamics with new common variables - for people with a diversity of geographically-specific interests. If you can think of any uses for such a game, or would like to argue how such a game would be inaccurate or impractical, please visit Open Biodemometrics Forum :: Index.

 

[blueroomelectronics]

How can something with so many words be so vague.

Why not just write a program for a touchscreen computer or an iPhone / iTouch? Do the game pieces have to be 3 dimensional or will a 2D representation work?

 

[jasonbe]

How can something with so many words be so vague.

Why not just write a program for a touchscreen computer or an iPhone / iTouch? Do the game pieces have to be 3 dimensional or will a 2D representation work?

I am not sure what you mean by vague – that I have not decided on a final design plan, that I haven’t described all of the many things that my game could model, or something else. I prefer a peripheral because it is more accessible to a group of people than a keyboard - as well as, I think, offers a better representation of the geographical location of the pieces. I could use a touchscreen computer or an iPhone / iTouch to remotely communicate with players who have the same game – though I might have to learn how to encode information with sound first.

 

[jasonbe]

I’ve decided to go with a grid of aluminum strips, though in case anyone finds a stiff flat sheet with the resistive properties that I was looking for, I’d still be interested. Is there a best way to connect resistors between a single conductor and each strip - to encode each strip with different resistances and complete the circuit?

 

[jasonbe]

How can something with so many words be so vague.

Why not just write a program for a touchscreen computer or an iPhone / iTouch? Do the game pieces have to be 3 dimensional or will a 2D representation work?

Maybe my response sounded vague because my short term plans for the game aren’t as closely related to what I would like to eventually use the game for as I would like them to be. I’ll try to be more specific by saying that I would like to use my game design as a model of how human traffic patterns defined by grouping people according to biometric data develop in time - and, specifically, how five different populations - represented by each game piece, having groups in each population defined by three gait types that are common to all five populations - represented by three displays on each game piece, interact and develop in changing locations. I don’t know if these types of relationships actually exist. I imagine that the type of aerial photography - that could gather gait data of large groups of people for analysis to identify groups and prove or disprove that a relationship exists, is probably mostly used for military purposes. If the data were available and relationships were found to exist, then I think that it would be interesting to investigate areas where similar patterns were found for a reason for these similar occurrences. However, even though there are many factors effecting people’s body language, including their race, skeletal structure, muscle distribution, body fat distribution, health, time of day, and changing mood – I think that not overlooking the possibility of such relationships that could better define the chemical and social nature of human development is important, if for no other reason than these relationships could help define people and human development in more dynamical, common terms. Have you heard of any such studies?

 

[dknguyen]

I’ve decided to go with a grid of aluminum strips. Is there a best way to connect resistors between a single conductor and each strip - to encode each strip with different resistances and complete the circuit?

Please explain more. But I would think you need to make a board of metal plates and have each one connected to it's neighbours by a resistor (to simulate the resistive sheet you are looking for). I don't see how you are going to track down where a playing piece is along a conducting strip after you've figured out which strip the playing piece ison.

 

[jasonbe]

Please explain more. But I would think you need to make a board of metal plates and have each one connected to it's neighbours by a resistor (to simulate the resistive sheet you are looking for). I don't see how you are going to track down where a playing piece is along a conducting strip after you've figured out which strip the playing piece ison.

You might have a better idea. I haven’t really thought about it that much. I actually thought of this idea while considering one of your prior posts. I’m running out of time on the public computer that I’m using, so let me know if this explanation is too brief. Basically, I plan on using a plurality of parallel metal strips in two perpendicular x and y directions, insulated from each other, to identify locations according to where electrical contacts on the game pieces contact these strips. For the sake of simplicity, I’ll just describe the strips in the x directions first. At one end of the game board I intend to electronically connect all of these strips. On the other end of the game board, I would like to close the circuit by connecting each strip to one conductor – to conserve the amount of pins that I have to use on a microchip. However, to encode each strip with different electrical characteristics, I need to make the electrical characteristics associated with each strip different. So, basically, while all of the strips connect to the same conductor, each strip has to connect differently, through a different circuit, so as to distinguish the electrical signal associated with each strip. I believe that the best way to do this might involve connecting each strip to a circuit in such as way as to make the electrical characteristics associated with each strip – that connect to the same conductor, as distinguished as possible. In doing this, I might be able to save parts by using the component(s) associated with each circuit connected to each strip in another/ other circuit(s) associated with (the) other/ another strip(s) as well. Encoding strips in the y direction in a similar way might allow me to identify game pieces according to coordinates defined by intersecting x and y strips. Does this make sense?

 

[jasonbe]

Looking through some of the posts in this forum, in addition to all of the interesting ideas and thoughtful questions, I can’t help but notice that there has been a tendency to refer me to already made products. Without depreciating the value of these already made products – but, also, without keeping organized records of the cost of resources for my present project, I would just like to point out that the cost of these already made products may make them inaccessible for small projects such as the one that I am working on. I’m afraid that this might be an example of overlooking a large market, who, when having to decide between elaborate technologies and manual methods, choose manual methods because products and resources aren’t designed and made available for their price range. This could be one characteristic of populations that I represent on my game board, though I would like to focus on identifying psychological qualities and dynamical development characteristics of populations - that may be able to be identified by grouping people by gait type, and that might be overlooked as understanding between cultures is still broadening.

 

[blueroomelectronics]

What commercial product is remotely like your vision? I couldn't think of anything that fit with your concept.