Pressure Sensor Trouble

Other Hardware Sensors
1

I have been trying to use a pressure sensor to sense air pressure in PSI.

Im using an Arduino Uno.

Im using this one.

I is 5V and it is supposed to sense 0-100PSI

It has 3 wires.
Black is -
Red is +5
Green is Sensor output. I have this one hooked up to Analog 0 on the Arduino Uno i'm using.

Anyway, i get the same reading from the Green sense wire no matter what pressure it sees.
It is always 4.95V.

I have tried it a 40 PSI, 30 PSI, 25 PSI and also disconnected from the pressure tank.

The sensor has the following documentation:
Output: 0.5V~4.5V linear voltage output. 0 psi outputs 0.5V, 15psi outputs 2.5V, 30 psi outputs 4.5V.

So first of all 4.95 is more than the 4.5 that they mention.

This makes me wonder if I have it hooked up wrong?
I have the red +5 going to the +5 pin on the uno, the black - hooked up to the gnd on the Uno, and the green output on the Analog 0 pin on the uno.

This is the code im using:

const int analogPin = A0;
float inputP1;
float voltageP1;
float psiP1;


void setup() {
 Serial.begin(9600); // open the serial port at 9600 bps:
}


void loop()
{
 inputP1 = analogRead(A0);
 voltageP1 = ((float)inputP1* (5 / 1023.0));

 psiP1 = ((float)inputP1/1023*100);


Serial.print("VOLTAGE = "); 
Serial.print(voltageP1);
Serial.println();
Serial.print("PSI = "); 
Serial.print(psiP1);
Serial.println();
Serial.println();
Serial.println();


 delay (500);
}
2

Also I have confirmed the reading by using a volt meter to read the green output wire rather than that Uno.
I get the same results.

3

Please edit your post to add code tags.

That is the symptom of a faulty ground connection. Are you sure that you have made a good ground connection?

Recheck all connections, and use your multimeter to verify connection continuity, as well as proper sensor function.

4

You can try the code below. You may have to adjust the mapping numbers (0-100), But this may help you get closer to what you are looking for...
Let me know if this helps...

int PS = A0; // Pressure Sensor     
int PSR = 0; // Pressure Sensor Reading


void setup() {
  Serial.begin(9600);

  pinMode(PS, INPUT);


}

void loop() {
  PSR = analogRead(PS);
  delay(250);
  PSR = map(PSR, 0, 1023, 0, 100); //Changes voltage into PSI.. Analog--->Digital
  Serial.print("Pressure: ");
  Serial.println(PSR);
  Serial.println("   "); 
  delay(250);
}
5

Read the reviews. Seems like about a 50/50 failure rate. I have read on a lot of automotive sights that these cheap Chinese sensors are a gamble.
Also the specifications are wrong. At 0 psi it should read .5V and at 100 psi 4.5V.

6

detown:
Also the specifications are wrong. At 0 psi it should read .5V and at 100 psi 4.5V.

Actually 10% of VCC @ 0 psi and 90% of VCC @ 100 psi.
Sensors like this are ratiometric, and 5volt is never 5.000volt.
Therefore better to code in A/D values, not in 'volts' (you're not making a voltmeter).
Test sketch attached.
Leo..

const byte pressurePin = A0;
float sensorType = 100.0;
const int offset = 102; // zero pressure adjust
const int fullScale = 922; // max pressure adjust
float pressure; // final pressure

void setup() {
  Serial.begin(9600);
}

void loop() {
  pressure = (analogRead(pressurePin) - offset) * sensorType / (fullScale - offset);
  Serial.print("Pressure: ");
  Serial.print(pressure, 1); // one decimal place is all you're getting with a 10-bit A/D
  Serial.println(" psi");
  delay(500);
}
7

Thanks for the explanation.
Karma added.