For a project, I have to find the position of a finger on a line. Like a touchscreen but on only one dimension. For that I thought to use a resistive wire, then to read the voltage with an analog pin. But the wire must measure between 25 and 75 cm with at least 1k ohm.m to limit current and I've look on many websites and I can't find this kind of wire (or plate, this will also work). Does anyone know something like this? (I also try carbon on paper, it works but not really reliable and linear).
I thought about using a capacitor to have a similar behavior, but I have two problems with that. The first is that the reaction must be fast (at least 1kHz) and accurate and the second is how to correctly charge the capacitor from the touch of the finger? While the resistive wire would be simple and fast.
But the idea of the heating elements is precisely to have a rather weak resistance. I found heating wire up to 100 ohms / m. But the arduino will certainly not support 5 with such a low resistance.
Ok thank you I will try that then And if someone by chance knows how to solve the problem of loading a capacitor through a contact, it will help me for another part of the project, otherwise I will do another topic elsewhere.
Maybe Nichrome wound on a plastic or wooden dowel to increase the resistance per length? With an adjacent winding of fishing line to prevent the nichrome windings from shorting together:
n is the number of turns of Nichrome Wire (and, is actually the same value as before)
D is the diameter of the Dowel that the Nichrome and Fishing Line are to be wrapped around (essentially the core of the coil).
dN is the diameter of the Nichrome Wire
D + dN is the diameter of a loop of wire, from the center of the wire
W = 100R/ρ
Where:
W is the length of the Nichrome Wire in cm
R is the Resistance of that length
ρ is Ω/Meter
If we combine those these three formulas and solve for D, we get a tool for working out a Diameter for the dowel that will produce a sensor at the desired length:
Excellent work but too much theory.
Nichrome wire diameter 0.1mm = 240 ohm/m for 5m length = 1.2k, and where to find such wire?
0.1mm will be to hard to put on th stick with fishing line.
I can't really use the winding, because with the analog of the arduino and a wire of 25cm I have a presicion of 0.25mm (very theoretically) and if I do that I will certainly lose precision and I would like to keep the wire quite flexible and thin (not much more than 1mm).
I am not very familiar with the capacitive sensor, how to make one with a wire? (1kHz is probably too much, but I want to be sure that the slightest movement is detected.)
Potentiometers are, in general, made with rigid tracks, but if I'm wrong, what is the simplest solution to extract the wire, the potentiometer or the resistance?
I would like to be able to detect the very small and fast movements that could happen once the finger is set. Being able to accurately determine the movement speed will certainly be useful too. it's still a prototype, I do not know exactly the precisions and speeds needed. That's why I'm looking for great precision even if it's too much.
And if someone by chance knows how to solve the problem of loading a capacitor through a contact, it will help me for another part of the project, otherwise I will do another topic elsewhere.
