serveral pressure sensors get strange output/not working

Hello there,

i'm quite new to Arduino programming. So i encountered an issue i'm not able to solve on my own so far.

For the Project I'm working on I need to measure a Force applied on a surface. The mechanical part of it is no problem, but the electrical part is not my field.

So I found this tutorial where they use a thin-film resistor, hooked up to an analog pin. I have tried this kind of circuit for serveral potis as well, but the force sensor won't do it for me.

I have an Uno board and two of those:

https://www.conrad.de/de/p/joy-it-sen-pressure10-1-st-passend-fuer-arduino-asus-asus-tinker-board-banana-pi-beagleboard-beaglebone-c-2205376.html

So the first question would be: Does anyone know anything about this kind of sensor? It says 10kg max, but without even reaching this value I'm at 1023 in the seriel monitor.

Another issue: connecting both and just pressing one will give me a value on both of them, i even get value's if none is connected to the analog ports.

Thanks in advance, teido

Here is my code:

int val1 = 0;
int val2 = 0;

void setup() {
  // put your setup code here, to run once:

  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:

  val1 = analogRead(A0);
  val2 = analogRead(A2);

  Serial.print("sensor1   ");
  Serial.println(val1);
  Serial.print("Sensor2   ");
  Serial.println(val2);

  delay(1000);

}

What I can't see is any labeling on the three pins, like Vcc Out and Gnd? My best guess is you have a strain gauge in series with a resistor (R1) and likely a cap across the output. The strain gauge acts as a variable resistance with resistance changing based on applied force. They do not seem to mention output range of voltage based on applied force? They also do not get into mounting suggestions? What you have is a pretty crude setup. If you have an ohmmeter you could measure across R1 on the board and then measure across the strain gauge in a static state, just sitting there with no force applied. This with the module disconnected.

If this is just a series resistor with a strain gauge I can't see how you are getting 1023? The 1023 would indicate about a 5.0 volt in or if your Arduino is a 3.3 volt ref a full scale voltage. Unless something is not correctly wired?

Ron

Seems like a re-branded Keyestudio sensor.

0.5Kg, not 10Kg.

510k pull up without a capacitor fitted...

Would sort of work for one sensor, but could have cross-talk with two sensors.

Add 100n capacitors from each analogue pin to ground. Leo..

Sure does look like it.

Ron

What I can't see is any labeling on the three pins, like Vcc Out and Gnd? My best guess is you have a strain gauge in series with a resistor (R1) and likely a cap across the output.

The pins are labeled, it is just not as clear on the picture. Measuring directly on the strain gauge get's me the voltage as expected, ~5V when pressure is applied and 0V if not.

They do not seem to mention output range of voltage based on applied force?

The finished project will be calibrated and mapped onto the applied force. However, the exact value of force is not as important as the repeatability.

They also do not get into mounting suggestions?

The thin film Part will dissapear between two printed parts, embetted within some silcon due to the lack of detecting when I was just pressing with hard plastic parts.

But thanks for the answers; the solution with the capacitors just sorted it out. I did not have 100n, so I took 22n. Now it does exactly what it should do, thanks!

But as a researcher im curios why this worked, I'm just getting started with electronics, I'm working in applied Mechanics. You may got a short explanation or better keywords to look it up how and why this works?

greetings

The A/D should see a source impedance <=10k, according to the Atmel datasheet.
510k is a bit higher than that.
The capacitor acts as a voltage buffer, and gives the A/D a more solid source to sample from.
Leo…