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Post by guchioguchi on Dec 28, 2017 16:04:10 GMT -5
My knowledge of semiconductors and the like leaves a lot to be desired so forgive me if this is a dumb question:
Is it possible to use a Force-Sensing Resistor basically as a volume pot?
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Post by sumgai on Dec 28, 2017 23:12:17 GMT -5
guchi,
Hi, and welcome to The NutzHouse! 
In short, the answer is "depends". Certainly not mounted on a guitar, but in a stomp box of some sort, it might be possible. Used as a temporary effect, I can envision how a player would step on the treadle to force the volume up for as long as he/she stood there, and when they step back (off the treadle), the volume returns to the previous level.
However, there is no small amount of active circuitry involved. In the world of guitarists, the overriding principle is K.I.S.S. (except for us Nutz!), which abhors additional expense and the introduction of potential failure points. One has to wonder, why don't you just use a standard passive volume control and be done with it?
BTW, Interlink's trademark notwithstanding, the term FSR has been used in the guitar world for more than 5 decades, it refers to a Fender Super Reverb amp. I'll lay even money that I wasn't the only one to see your Thread Title, and scratch my head in puzzlement....
HTH
sumgai
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Post by guchioguchi on Dec 29, 2017 1:41:22 GMT -5
Haha thanks I was actually worried it would be confused as a fender special run. I was being vague because I’m paranoid somebody’s going to beat me to it (I doubt anybody’s actually even interested). Specifically what I’m after is sort of like a single mpc style drum pad that would open up the volume when I press it and close it back down when I release it, like a reverse kill switch without the kill.
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Post by ChristoMephisto on Dec 29, 2017 7:35:43 GMT -5
The way you asked in the first post sounded like you needed a spring loaded volume pedal that goes up but down in volume when the foot pressure is removed. Maybe a momentary latch pedal?
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Post by guchioguchi on Dec 29, 2017 13:19:29 GMT -5
That's kind of what I have going now, just with my hand instead of my foot? Using my hand is ideal in this situation since I have more control. But right now I have a kill switch with a momentary button that reverses the kill switch with the idea of making it kind of like a drum machine. I thought maybe a force-sensing resistor would make it more like the real thing, also giving me a little more expressive control.
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Post by sumgai on Dec 29, 2017 23:46:42 GMT -5
guchi,
One thing I can tell is this: you don't want the guitar's signal going directly through that resistor. As the resistor changes value, that will introduce noise, and probably some distortion, into your signal. IOW, what you hear out of the amp will not be very pleasant. Addtionally, as I said above, if this resistor fails in any fashion, your signal will likely be lost entirely. Although you could institute a bypass switch to restore the signal, in case of failure.
This is why I mentioned active circuitry. Digital or analog, what you want to do is use the FSR to control the gain of a standard analog amplifier device. This would let you adjust the amount of pressure needed to achieve a set range of levels, with the added benefit of not distorting your pickup signal. As above, a bypass switch would protect you from a suddenly dead output, whether it's a part that went bad or a just a dying/dead battery.
Feasible, but again, at what cost in terms of money and time. Have you given any thought to how you're going to mount it and actually use it?
HTH
sumgai
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Post by reTrEaD on Dec 30, 2017 13:02:27 GMT -5
My knowledge of semiconductors and the like leaves a lot to be desired so forgive me if this is a dumb question: Not a dumb question at all. An interesting one. Is it possible to use a Force-Sensing Resistor basically as a volume pot? Strictly speaking, no. It's the "pot" part that's the hangup here. Pot is short for potentiometer. A three-terminal device that can be used as a voltage divider. As the wiper is moved from one end toward the other, the resistance between wiper and one end decreases while the resistance between wiper and the other end increases. If a FSR functioned like a potentiometer, life would be good for your plan. Unfortunately it doesn't. It's a two-terminal device that decreases in resistance when force is applied. There is no corresponding resistance to a third terminal that increases when force is applied. guchi,
One thing I can tell is this: you don't want the guitar's signal going directly through that resistor. As the resistor changes value, that will introduce noise, and probably some distortion, into your signal. IOW, what you hear out of the amp will not be very pleasant. Addtionally, as I said above, if this resistor fails in any fashion, your signal will likely be lost entirely. Although you could institute a bypass switch to restore the signal, in case of failure. ime: 1 - A bypass is definitely worthy of inclusion, regardless. Even were it possible to use just a FSR as a volume control, one wouldn't want the requirement of pressing on it to allow sound in all circumstances. Sometimes one would want to play 'normally'. 2 - Distortion: I wouldn't anticipate distortion at any pressure or change of pressure on the FSR. 3 - Noise: External noise, particularly hum, should be expected if using just an FSR with no other circuitry. When sufficient force is applied, a FSD in series with the signal would do a reasonably good job of passing the signal to the output. But when released, it becomes basically open-circuit. Hum levels should approach the same as a cable without being plugged into a guitar. Or a guitar with a reversed-wired volume pot set to minimum value. Not good. If you have a cheap guitar on hand to use as a test-bed, you certainly could try it. I'm sure the result be something that gives you more expressive control than a 'reverse kill-switch'. But the hum issue with low or no pressure applied will probably make this at least moderately undesirable. JMO. |
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