DIY Force Sensitive Resistor Tutorial | Reverion ~ digital musical instrument diary
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- เผยแพร่เมื่อ 7 มี.ค. 2018
- How to make your own force sensor or FSR (force sensitive resistor) and use it for a simple thin xy-sensor in combination with a softpot.
Synthesis and visualisation through SuperCollider running on the bela.
Thanks . Very Useful .
very informative..... for me. I'm actually finding something like this. thank you
I'm glad!
You should add some bakground music man! Great work!
ptrertp Right, yes, I forgot about that! I'll add something fitting for the next one. Cheers!
Beautiful!
What code did you use?
Hi. Thanks for your info. I have a question. Why it has different sound along to position? FSR looks like symmetric structure...
That is from to the softpot on top of the FSRs.
Hi Erik! really good work! I'm trying to implement a digital musical instrument using this kind of FRS's. Do you think it's possible to get the "Y" value without using the softpot but only the FRS's?
Thanks! I think you're gonna have a very hard time making that reliable. Right now I'd probably recommend checking these sensors out instead if you can use I2C, you save a whole lot of effort for much better reliability and precision for not that much more money: shop.bela.io/collections/trill/
(not affiliated in any way, just think they're awesome)
@@eriknatanael ok thanks! I will check that out! My problem is that I'm trying to implement a gestural controller inspired by string instruments, so basically the idea was to use a matrix made of copper tape to simulate a fretboard and the strings. With this set up I can get the "Y" value, but the problem is that I would like to be able to play in different temperaments. So with this set up I can't really do it because I would have fixed "frets". I'm looking for a solution in which I could determine the position of those frets.
@@WindyChaos Okay, but if you are using frets you can have them change their pitch without physically changing their position on the instrument, right? If you want a sort of continuous DIY sensor you could try copying the approach of the Trill sensors by making a copper matrix where each cell is smaller than your finger, measure the capacitance of each pad and interpolate between them to find the current position.
@@eriknatanael Great I will consider all your advices! thanks a lot! I think I might buy the ribbons ( I need 6 haha)
If you're still looking at this comment thread, couple questions:
1) Does the sensor detect the degree to which you are pressing on it, or simply whether or not a force is applied?
2) How sensitive can the sensor be? Can it sense a very light touch?
Thank you!
1) Yes, the harder you press on the velostat, the lower its resistance, so the higher the voltage going to the analog input.
2) It can sense very very light touch! If you just have one layer of velostat that's all it can sense since you'll lower the resistance to the minimum with very little force. I found around 3 layers of velostat was kind of a sweetspot for my use.
Hey! How accurate is this? Like, if you touched it 50mm in and it made a 440hz sound, if you came back the next day and touched it in the same place, would it make the same sound? How much does the signal fluctuate? Like, if you hold your finger in the same place, is there a lot of noise causing the frequency to move up and down erratically, giving it a warbling effect? Because I tried this myself and thats what happened and I don't know if I did something wrong or if its normal!
This was a while ago so I don't quite remember, and I don't have any of these laying around anymore. I don't think they are very accurate, but if you are careful to line up the velostat with the right dimensions there shouldn't be much noise I don't think. They can be very sensitive though, and it's hard to keep your finger pressure constant. Note that where you touch the sensor shouldn't matter since it's an FSR and not a linear potentiometer/"softpot" (which I combine two of these with in the he end of the video). Personally, I wouldn't use these for pitch, use a softpot or something else for pitch.
@@eriknatanael Hey! Sorry I got confused, I was talking about the linear potentiometer, which I'm using to control pitch! But even if I keep my finger dead still on my one, the pitch still warbles slightly. I'm using some sliding window averaging algorithm in the code to smooth it out, but that adds a little lag to my performance. Is it normal for the pitch to warble like that?
@@WeirdSide The softpot should be able to give you a pretty stable reading. How are you wiring it?
is this essentially the same as capacitive touch? i.e. the velostat is just the dielectric layer between the two copper "plates". I've done this with a thin layer of rubber (because velostat seems to be nonexistent where I live). Also is the accuracy of the sensor sufficient enough to also calculate velocity - have you tried that?
Not quite, I don't know enough physics to know what a dielectric layer is, but this sensor works by the velostat having a variable resistance when compressed, resulting in a difference in voltage drop between the copper strips. A capacitive sensor instead would measure the additional capacitance of the skin when you touch the sensor. I have however started using capacitive sensors more and more in new projects.
This sensor isn't great for sensing velocity because of hysteresis, but I guess you could do it to some degree if your microcontroller can read the sensor fast enough.
Great job.
What is the width of copper tape?
What is the width of velostat material?
what if the width of copper tape is 5mm and velostat is 7mm, will it be a problem.
As long as the copper tape is smaller than the velostat so that the copper on the top and bottom of the sensor don't touch you should be fine. 5mm wide copper tape and 7mm wide velostat will give you 1mm on each side so I don't think that should be a problem. The sizes will influence the response of the sensor so you'll have to experiment with how many layers of velostat will give you the sensitivity you want.
are those 6 layers the 8 or 4 mil velostat?
I don't actually know, sorry!
@@eriknatanael BTW, what is the point of the two fsr's? The soft pot is an FSR as well. It should be able to sense both velocity and position if I'm not mistaken. Or are you doing something else I'm missing?
@@sabahoudini The two FSRs allow you to get some sensitivity side to side as well as how hard you're pressing down on them. The softpot doesn't really work like an FSR, but a linear potentiometer. On the FSRs it doesn't matter where you press whereas on the softpot it doesn't matter how hard you press (beyond a certain threshold). Unless you know something I don't in which case I'd love to learn about it. You can sort of tell how wide the thing pressing the softpot is, but only if you're gonna play it with just one finger (i.e. not have fingers pressed down "below" the highest pitch you're playing) and don't have it set up for two different pitches.
@@eriknatanael Well I may be understanding this wrong because I'm an electrics noob but a softpot is basically a voltage divider. If you could somehow hook up each side of the divider to it's own analog in pins you could both sense position and touch. The ratio of the two signals would be the position and the sum of the two signals is the velocity. However as I said I may have misunderstood how this works :P
@@sabahoudini I'm an electrics noob myself. Definitely let me know if you hook this up and try it out!