Project development: Creaky Floor

[EBK]

I built a quick version of the single vactrol circuit last night (I found two NSL-32 vactrols in my parts collection):


The results were so encouraging that I tore it apart to proceed with the two vactrol version without bothering to record a sound demo (I'll be able to make the same sound in the two vactrol version by leaving the return jack disconnected).   

The sound was reminiscent of the trick of rapidly toggling a pickup selector switch to cut the sound in and out.

[EBK]

The updated FSR pulse generator circuit schematic (MUCH simpler), with resistor values added:


I'll sketch up the other half a bit later.

[EBK]

Here is the other half of the circuit as it exists on my breadboard:

Edit:  I need to redraw this so it doesn't look so weird with how the send/return jacks are placed.   
Here is a more logical arrangement of the same schematic:


It works, and it is pretty interesting.  Hopefully, I'll be able to record a demo with sound soon.  To quickly test it, I ran clean guitar into the input and hooked a tubescreamer at max gain through the send/return loop.   

One quirk that I will have to think more about is that, with no force applied to the FSR, no LEDs are lit, and thus, no signal comes out.  This may be useful in some circumstances, so I may implement a toggle switch that optionally "corrects" this.

The thing that excites me the most about this project is that I finally get to share something new and original (as far as I know, anyway) with the community.   

[EBK]

Here's a demo with some sound.  I apologize for the low volume (didn't want to wake up my family).  In this video, I have the send/return loop connected to my mutron iii envelope filter, which gives this thing some cool trippy results. 
https://youtu.be/fXE0LhsIjqE

And here is one more demo, with a tube screamer this time:

https://youtu.be/2ceN_CLJLpU

[EBK]

Next, I need to tackle lining up the FSR underneath this (with something in between to protect the FSR and distribute the force across its surface):


Once I do that, I can try playing a guitar with both hands while controlling this circuit to see if there might be musical potential in this wacky idea. 

That actuator is avalable from smallbear:
http://smallbear-electronics.mybigcommerce.com/switch-actuator-for-b-o-b/

I got the FSR there too, by the way:
http://smallbear-electronics.mybigcommerce.com/alpha-membrane-force-sensor-mf-01/

[EBK]

Looks like the space between the actuator's external spring and the lid of the enclosure is pretty close to $2 USD (in US quarters) or 14mm. 

[garcho]

very cool, DIY "mash" switching, eat yer hearts out TC Elec

[EBK]

very cool, DIY "mash" switching, eat yer hearts out TC Elec

Wanna know the best part?

It works!

I'll have to add up the amount of change I used in the end.    Edit: Eight US quarters, with the FSR sandwiched between the top two.

More importantly though, an extra secret ingredient was required to get it working.  When I squeezed the FSR between my fingers, it worked perfectly.  When I squeezed it between two coins?  Nothing!  What was needed? Some blu tack.  I put some of that on each side of the FSR, and it worked. 

More demos soon! 

[bluebunny]

When I squeezed it between two coins?  Nothing!  What was needed? Some blu tack.

I'm guessing your coins were shorting out the FSR?  But repeated squishing of blutac will make it thinner and thinner, until...

I'd use a simple piece of paper.  Or a dollar bill.   

[EBK]

It appeared to be the opposite problem.  I theorize that, by being so rigid, the coins only contacted the FSR properly over a small surface area (due to the relief in the images on the coin faces).  The result was nearly no change in resistance from the zero-force high resistance. The blu tack filled in the spaces, allowing more uniform pressure.

[EBK]

The spring on the actuator is getting a bit out of shape from freely sliding around on top of the stack of quarters.


To solve this, I've decided to dig out my manual 3D printer: JB Weld and miscellaneous hardware. 

[highwater]

With blu-tack and JB weld in there, it really needs duct-tape now for the cob-jobprototype trifecta.

[marcelomd]

Nice!
You can also try plastic or hot glue (just a drop on a surface, let it harden) washers. Blu tack would slowly creep out with repeated presses.

[EBK]

With blu-tack and JB weld in there, it really needs duct-tape now for the cob-jobprototype trifecta.

The stack of quarters is held together and attached to the lid using gaffers tape (seriously). 

[EBK]

Nice!
You can also try plastic or hot glue (just a drop on a surface, let it harden) washers. Blu tack would slowly creep out with repeated presses.

I might try to find some rubber gasket material next.

[duck_arse]

as R.G. might say, "mouse pad, cobber!"

[EBK]

as R.G. might say, "mouse pad, cobber!"

Maybe if I can find one of those super thin ones.... 
I'm thinking jar lid gripper at the moment.

[EBK]

I found a thin mousepad in my office, and I cut some circles out of it for testing.


If this works, it would save me $0.75 because the two pad discs (when uncompressed) are the same thickness as three quarters.   

[Kipper4]

I was going to suggest neoprene. Time to hack that gimp suit up Eric
Or maybe some rubber 1/2" tap washers.

[EBK]

Ok, preliminary results suggest the mousepad is too soft.... 

The actuator has a very limited travel distance to go from minimum to maximum loading force. The mousepad couldn't even deliver the amount of force needed to light the first LED.  I need something that more closely approximates a thin layer of blu tack.  My present thought, based on my observations of the extent that the blu tack spread out, is that blu tack is in the lead.