Any experience with FSRs?

[Mark Hammer]

I included two force-sensing resistors in my latest Small Bear order, and was pleasantly surprised by both a) how little force it takes to make them change resistance and b) just how high AND low the resistance can go.

It would be a pretty trivial matter to make an op-amp-based overdrive, whose gain was set by a resistance to ground from an inverting pin, use a "default" maximum value (e.g. 500k), with the FSR in parallel, and press on a pad on top of the chassis with your foot to reduce the FSR resistance and increase the gain of the op-amp.

It could also be used in parallel with the LFO rate pot of a phaser.

Lotsa interesting applications.  So, any experience using them, here?

[EBK]

I've always been curious about these as well.  How "touchy" are they?  Can you maintain a particular resistance value decently with a finger?  Is there any noticeable hysteresis?

Could you sub one for a vactrol's LDR and make something crazy/fun (note, "useful" and "practical" are of secondary concern to me here  )?

[Hatredman]

Not only that: do they return to the nominal resistance after you release your finger, or does it drift a little?

Scarlett Johansson uses a Burst Box with her Telecaster.

[bluebunny]

I had a notion to use something similar (QTC) sandwiched between two skinny picks as a squeeze-sensor for a wah or similar, but never got round to it...   

[deadastronaut]

always fancied playing with those FSR's  a while back, they were very pricey though..

[Mark Hammer]

In my limited and brief experience, they do return to max resistance quickly.  I suppose one would have to gather continuous data from one to have some sense of how "touchy" they are, but preliminary use suggests no more touchy than photocells.

And yes, one other potential use is as part of the resistance to ground that sets the resonant/centre-frequency of a bandpass filter.

The resting (untouched) resistance is in the 10M range, and squeezing one brings it down just below 1k.  This means that placing one in parallel with a 500k speed pot on an LFO would have negligible effect on max pot resistance (i.e., slowest speed setting), ad pressing it could bring the combined parallel resistance up to fastest speed.  So, as ramp-up/ramp-down retrofits go, actually pretty simple and non-invasive.

I think it's about time we collectively started pondering uses of these very useful things.  As for price, I don't know how Steve brings them in for such a low price, but he does.  Sparkfun sells them for $6.95 USD and Small Bear has them for $2.95 USD.  They are certainly not VERY cheap, but when one considers just how much functionality can be produced with one simple part, that's actually a pretty good deal.

[potul]

Interesting

The new TC electronics pedals are featuring a pressure sensitive stompswitch that can act as an expression pedal (what they call MASH).
And I remember seeing another pedal compnay in the last NAMM(I don't recall exactly), that includes some pressure-sensitive external expression pedal.

Maybe these could be used to create something similar.

[smallbearelec]

I don't know how Steve brings them in for such a low price

No magic; Alpha is a high-margin line for many shops. In the early days, I worked my way up to being able to make the minimum order quantities to buy directly from the factory. Once I could do that and my orders got large enough to justify ocean shipping (for which thank your favorite boo-teek pedal makers), I was on my way.

FSRs: I expected to have a large market for these parts--especially among the synth people--and I priced them so as to be affordable for manufacture. They have not been a blockbuster, but maybe that's because, as you note, people have to figure out what to do with them.

one other potential use is as part of the resistance to ground that sets the resonant/centre-frequency of a bandpass filter.

Yea, try setting up a Twin-T "Electronic Bongo" and adding an FSR in parallel with that resistor. I bet that you would get a usable "boiiinnnggg".

[EBK]

Some good info here: https://learn.adafruit.com/force-sensitive-resistor-fsr/overview

[Mark Hammer]

Yea, try setting up a Twin-T "Electronic Bongo" and adding an FSR in parallel with that resistor. I bet that you would get a usable "boiiinnnggg".

Instant tabla!     Allah Rakha watch out! 

[tonight, we ride]

I've never used what I would call an FSR, but have used strain gauges quite a bit in industrial testing. It looks like the two are identical in concept, and only different in their packaging.

We typically used strain gauges as one leg in a wheat-stone bridge configuration. The resistance would change, with any stress in that plane, and generate a small differential voltage (between the two legs of the bridge) that ended up at a data acquisition device... but they definitely don't need to be used that way. When installed correctly they are very stable and predictable in their resistance at known applied forces. If you've ever heard of a "load cell" it is simply a material that already has an FSR, or strain gauge, attached and has a known, calibrated range (ie X lbs. of force applied to the load cell = X resistance).

Applying predictable pressure for variable control may be difficult unless you have really steady feet, but could be really fun for a feedback setting on a delay, or something where less predictable results are desirable.

On-Off function for a wah pedal seems like a good candidate for a project, or really switching of any kind.

Maybe a momentary kill switch for vocals or guitar?

Wait... is this getting too close to being a "burst-switch?" What thread am I in???

[Mark Hammer]

I would think that putting one of those adhesive felt pads you can buy for furniture legs on top of the FSR would distribute and somewhat attenuate foot pressure, such that it wouldn't be so twitchy.

Easily adapted to the EHX Soul Kiss circuit - http://topopiccione.atspace.com/PJ10EHSoulKiss.html.  Just substitute the FSR and a suitable parallel resistor for the LDR and transistor part, "Bite down" (as my dentist says), and away you go.  Just make sure the FSR is sandwiched between two layers of something that can withstand your bite.

[EBK]

Just make sure the FSR is sandwiched between two layers of something that can withstand your bite.

A couple of guitar picks might do nicely for that.

[EBK]

Another thought:  if you put a spring between your foot and the sensor, it would translate foot travel distance to force while the spring is compressing.  Might provide better feedback to the user....

[Kipper4]

Any data sheets or links to buy there please.

[Mark Hammer]

Any data sheets or links to buy there please.

http://smallbear-electronics.mybigcommerce.com/new-category-4/

[deadastronaut]

the price really dropped on those FSR's...they were 15 quid a pop at one stage...

[Kipper4]

I've seen that type of thing in euro rack gear.

I'm thinking because of the lowish range of resistances (10k~40k) It might be used as a parallel resistance.
Maybe as suggested already for a svf filter or a speed mod for a phaser/tremolo.

or even as part of a voltage divider in a x fader.

Hmmmm


Thanks for the link Mark. Nice price too Bear.

[Kipper4]

Oops Stupid question Post deleted.

I just forgot to read. all the posts. DOH.