How Calculate the number of chips

[JMLB 24]

I am trying to find a way to measure how many poker chips in a stack. My though was to put a peizo and put your stack on that. I don't know enough about peizo though. Any thoughts would be appreciated or if you would use some thing else.

[bluehash 1,581]

A pressure sensor should do it. If you know the weight of 1 chip, you can calculate the total chips by:

pressure/pressure of 1 chip.

[JMLB 24]

that is sorta what I am trying to accomplish with the piezo. I have a piezo at hand and they are cheap. any link for a pressure sensor?

[gatesphere 45]

The piezo is a very poor choice for this kind of application. They are much better suited to vibrational sensing. You might want to try one of these: http://www.adafruit.com/index.php?main_ ... e85b51e559

 

They're available elsewhere cheaper, but that's just the first place that I remembered had them for sure.

[bluehash 1,581]

I was going to say the same thing, but point to sparkfun:

http://www.sparkfun.com/products/9375

 

make sure to read the force/Vout curve before you buy it. It is a tiny bit non linear.

[JMLB 24]

The piezo is a very poor choice for this kind of application. They are much better suited to vibrational sensing.

 

after reading some more, you are right, they measure the change in pressure. Thanks. i was hopping not to use presure sensors since they are expensive. But I guess its the best way.

[RobG 1,892]

How about this if you want to use piezo, mount it at some height, then put the chips below, ping and measure the time it takes for the ping to return, just like distance meters do.

 

And how about optical way, for example you can have a tube, on one side detectors, on the other LEDs, you wouldn't have to have as many detectors and LEDs as chips, because you would scan and detectors would work diagonally.

[JMLB 24]

I do like the ping idea though the distance meeter usualy have a minimum distance. I also don't know if its accurate enough to detect the difference of 1/4 inch? I might try it though and see. I also don't quite understand what you mean with the sensors being diagonally? can you explain a little more?

 

thanks

[RobG 1,892]

You could mount piezo 12 in above the bottom, and allow up to 6 or 8 in stack.

 

So the idea is to have a tube (c shaped or full) with a slit on both sides. LEDs and detectors would be mounted ~1 inch away from the tube. The you scan through LEDs and see which detector "sees" the LED. When you have enough chips to cut off the light from the parallel pair, the detector will still "see" the LED above, the next chip will cut that off but that one above will still be visible, and so on. It all comes down to geometry and finding the right balance between the number of parts, accuracy, and the dimensions

[zeke 693]

You will be constructing an apparatus to do this measuring so I think you should approach the problem by measuring the length or height of the stack.

 

Think of a modified caliper. It knows the length. Just divide that length by a known quantity - the chip thickness, and you have the number of chips.

 

You will have to set a practical limit on the length that you will measure otherwise the resolution will be diluted and you may be off by one chip count - error factor.

 

I see a sliding T-stick that you would stand up beside the chip stack and measure its height above the table. You slide down the T to the topmost chip and the digital readout tells you how many chips it thinks is there.

 

If you want to go contact-less then you will have to build a comparator mechanism. It will sense the presence of chips up to the last chip and then sense nothing after that. An electronic ruler.

 

Think of a stacked opamp configuration that measures a voltage ladder. If the applied voltage is within an opamps operating input window then that opamp will turn on.

 

IMHO, the solution is an A2D input circuit of some sort.

[JMLB 24]

I did think og using a lieter pot rather than a rotary pot and have the user slide it up even with the stack.

 

I think RobG's Idea with the LED might be a good Idea LED are cheap and I can find them every where