Hello everyone,
I need to use a key (something like the keys of a keyboard or a response box) that also allows me to measure the pressure exerted by the user.
That is when the user presses the button, not only I record what they pressed and when, but also how strongly they pressed.
I should also mention: I need this for an experiment, therefore I need the sensor to be accurate. I don't know the proper terminology but basically, if the participant is applying, say, 345 grams of pressure on the sensor, that's what the reading should be, with as little error or jitter as possible.
Is there anything like this?
Thank you in advance for your time and any suggestion you may have.
Sounds like you may be able to get away with force sensing resistors.
A force-sensing resistor is a material whose resistance changes when a force, pressure or mechanical stress is applied. They are also known as "force-sensitive resistor" and are sometimes referred as "FSR".
marco_c:
Sounds like you may be able to get away with force sensing resistors.
A force-sensing resistor is a material whose resistance changes when a force, pressure or mechanical stress is applied. They are also known as "force-sensitive resistor" and are sometimes referred as "FSR".
I did think of using a force sensitive resistor but I keep reading everywhere that they are not accurate at all. Is there such a resistor with high accuracy?
Thank you, I am looking at some tutorials like this: https://www.youtube.com/watch?v=LRd3W_p8PJ4
Do you think I could buy just the strain gauge (the little film) put it on a small piece of plastic and put a key on top? So that when I press the key, this presses on the gauge and I can record the amount of pressure?
Also, how precise would that be?
I'm a bit surprised that there's not a straight solution to this ^^ I'm sure someone else needed the same thing before...
I keep reading everywhere that they are not accurate at all
Probably because the people using them are treating them like a linear device. They need to be normalised to a curve and will definitely be more accurate in some parts of the range than others, so it depends on your application and the resolution of the analog to digital converter you use.
marco_c:
Probably because the people using them are treating them like a linear device. They need to be normalised to a curve and will definitely be more accurate in some parts of the range than others, so it depends on your application and the resolution of the analog to digital converter you use.
I had taken a look at that website, but it seemed to me that those sensors were also not very accurate.
For instance, for the FlexiForce A201 Sensor it says Linearity (Error): < ±3% of Full Scale (Line drawn from 0 to 50% load).
This is probably what you were referring to. I'm not really sure what it means to "normalise to a curve" (sorry, I'm a psychologists ^^'
Any chance you could point me to a tutorial that explains how to do this normalization and what it means?
it seemed to me that those sensors were also not very accurate.
State the accuracy that you require.
Frankly, I find it very difficult to imagine what "high accuracy" of finger pressure (force) would mean to anyone, or why someone would want to measure it "accurately".
How could a person even guess what force they are producing with a finger, and why would linearity matter?
Keep in mind that Pressure is Force per Unit Area. Use a precision gram scale to measure gram-force accurately.
Maybe you should start from actually explaining what accuracy you are looking for? Over what range of force (345g is just one value)? What is the accuracy of your Analog to digital converter (ADC)? Are you looking for accuracy or repeatability (ie, do you care that the force is x or are you just comparing relative forces)?
You say you don't want jitter, but that is not about accuracy. It is often about how reliable the ADC and the power supply are or the circuit around the sensor
Sensors are hardly ever linear across their full range, some sensors are no linear at all. Normalising (or calibrating) the sensor is about mapping the non-linear sensor to a calibrated output. This could be a calculation or a lookup table with interpolations or some other method. It all depends on the sensor output, the range you are calibrating, etc.
My advice is that if you are not experienced in this you should contact a supplier of sensors and describe what you want to do. They will be able to advise specifically for your situation.