Ordering a flexible conductive sheet or a pressure pad doesn’t just work straight out the package – it requires a little hack adding a top and bottom. What I’ve done is sandwich a pressure sensitive conductive sheet – known as Velostat – between two pieces of felt. I then stitched some conductive thread through each piece of felt – this applies a current to the pad and when the sandwich is put together, the circuit is complete. The Velostat acts like a resistor – the value changes when pressure is applied. It’s then just a case of writing out Arduino Sketch code that tells the LED to come on when the pressure reading goes over a certain threshold.

DIY Velostat Pressure Sensor Momentary Switch

I wanted to see how well velostat (conductive fabric) worked and how it would behave. It seems to work really well!

I first made a sensor out of some copper sheet material, some foam tape, two pieces of wire, a small 1 cm x 1 cm piece of velostat and some sticky tape!

This is just a prototype and may not be my final version of the sensor.

I found from measurements with my multimeter that when the pressure sensor is not touched the resistance across the wires is 30 kΩ. When pressure is applied it drops to 1 kΩ. That should be more than good enough for the purposes of detecting a key-press!

I then wrote some quick test code for the arduino because I’m leaning towards using an arduino for the microcontroller:

 




/*

Pressure Sensor test Code
 
*/

// These constants won't change.  They're used to give names
// to the pins used:
const int analogInPin = A0;  // Pressure Sensor connected to A0

int sensorValue = 0;        // value read from the pressure sensor via the amplifier stage
float outputValue = 0;      // value output to the Serial port

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600); 
}

void loop() {
  // read the analog in value:
  sensorValue = analogRead(analogInPin);            

  // print the results to the serial monitor:
  Serial.print("sensor = " );                       
  Serial.print(sensorValue); 
  Serial.println();
       
  // wait 10 milliseconds before the next loop
  // for the analog-to-digital converter to settle
  // after the last reading:
  delay(10);                     
}

Here is a graph I made from the serial monitor results. It looks very similar to the simulated oscilloscope trace from the first post!

The results from the serial monitor

So now we have a valid method of reading key presses we need to scale things up – and shrink a few things down. I

VELOSTAT PRESSURE SENSOR MOMENTARY SWITCH

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