Looking to use QTC Pills as a presure sensor for a USB dancemat project

[ericgibbs]

We talking Quantum Tunneling Compound Pills?? I am confused, never heard of a Q-Pill till now that is. Can anyone elaborate while I look it up..please.

Cheers,
-BaC

Morning BaCaRdi,

They are quantum tunnelling compounds, they are small square pills or short lengths of cable.
Resistance range with pressure megohms to milliohms, currents in amps.!

 

[AllVol]

Morning BaCaRdi,

They are quantum tunnelling compounds, they are small square pills or short lengths of cable.
Resistance range with pressure megohms to milliohms, currents in amps.!

It's the same principle as that of using conductive foam (like that used to protect CMOS chips during transport, etc.) between two pennies. Wire V+ to one penny, the other to ground. The more you compress the foam by squeezing the pennies together, the less resistance, and more current between the pennies. Forrest Mims showed it in his Engineer's Handbook years ago.

 

[BaCaRdi]

Morning M8, well it's just about afternoon on this coast
Cheers for the reply.

Aye,I did some research, all I can say is I want some! I already order some samples..lol Really kewl stuff I have to say, and the pressure sensitivity gave me an idea as an input device

-BaC

Morning BaCaRdi,

They are quantum tunnelling compounds, they are small square pills or short lengths of cable.
Resistance range with pressure megohms to milliohms, currents in amps.!

 

[prprog]

Damn, I can't believe that maplin have sold out of QTC pills... They were showing 90 packs in stock just before the weekend. Doesn't look like I'll be getting my parts in time to build my project over the long weekend then Well, I can be getting on with the main construction while I wait I suppose.

Also, another idea is to used the rubber from Trucks/Cars tires inner tubes (there are very few since most tires don't used it any longer) anyway... the rubber acts as a variable resistor under preasure. You need to make a interlock pcb trace and put the rubber over it. The change in resistance is very low but using a comparator set to very low voltage you can detect when it is press.
(you may need do a little sanding on the side of the rubber that will contact the PCB trace).

 

[3v0]

I was under the impression that the QTC technology was supposed to be more linear then conductive foam or rubber. If not why bother with it?

One of the things I recall is that it was conductive enough to be used directly as a switch without a comparator or A2D conversion.

 

[ericgibbs]

I was under the impression that the QTC technology was supposed to be more linear then conductive foam or rubber. If not why bother with it?

One of the things I recall is that it was conductive enough to be used directly as a switch without a comparator or A2D conversion.

hi 3V0,
IIUC the black conductive foam changes resistance due the applied pressure due to the compression of the foam,
which forces out the 'air pockets' within the foam.
This increases the total surface contact area within the foam and so the resistance falls.

The foam does dry out and it changes resistivity/sensitivity with time.
I believe there are applications where using black conductive foam would get the job done.

I would doubt if foam has the same current carrying capabilty as QP.

The quantum tunnelling compound is a totally different technology to foam.

 

[Amphetamine]

Hi, sorry I've not posted to this thread for a while, had to put the project on hold due to an expensive set of repairs to get my car through MOT....

I've got all of my parts now and have been doing some testing.

With 12 Qpills the change in resistance is almost digital with the weight of a human stepping on the tile, so I'm going to try building the project with the pad PCB wired directly to the Qpill sandwich and out to the ground point without the use of comparitors.

The build will take place over the next couple of weeks, so I'll keep you updated as to how it all goes.

On a side note, have aquired some lovely arcade button spares to use as navigation buttons drilled into the project box.

Amphetamine. if you'd like we could collaborate on this project/design, it'd be nice to work with someone.

Certainly, I'll be starting a build diary thread on the stepmania forums soon, so feel free to contact me here there or via pm .

 

[ericgibbs]

With 12 Qpills the change in resistance is almost digital with the weight of a human stepping on the tile, so I'm going to try building the project with the pad PCB wired directly to the Qpill sandwich and out to the ground point without the use of comparitors.

hi,
I would appreciate any results you get for the QPills, when you have completed the project.

 

[BaCaRdi]

Ditto, very interesting stuff! Thanks to being here, or would never had known what a "Quantum Tunneling Compound" was..

Cheers all,
-BaC

hi,
I would appreciate any results you get for the QPills, when you have completed the project.

 

[Amphetamine]

Finally got it all hooked up for in-game testing tonight.

There were a few accuracy issues that would have been solvable by tweaking the seating of the tile a little, but the main issue is the release time. Unfortunately the QTC Pills take longer than expected to return to an insulator. Some patterns which have very rapid steps on the same tile just arn't possible using this mechanism as the Qpills don't return to their rest state before the next step.

As it stands I've removed the Qpills and gone with a ring of foam around the edge of the tiles, allowing the ALU plates to be a direct contact, which is working much better. I'll see how this lasts over the next few weeks and see if I can come up with any other ideas.

Oh, this is the final result if you're interested:

**broken link removed**

**broken link removed**

Covered the MDF with a black marble effect fablon.

Somwhat disapointed that it didn't work as intended, but at least I still have a working unit