# 0.5 - 4.5v pressure sensor

Hi all,
I’m wanting to log/capture data from a pressure sensor into the Arduino.
The sensor gets +5v and ground and gives a 0.5v - 4.5v voltage back, linearly from 0 - 15psi.
(it’s an automotive style sensor where the controller perceives < 0.5v is open circuit and > 4.5v is a short).

I can’t get my head around the scaling to give me an answer in psi???

I can read from the analog pin and get a 0 - 1023 result,
but I’m stuck at the maths where I use the reference voltage to convert it to meaningful psi, especially when 4.5v is full scale and not 5v.

Any ideas??
Thanks!

Something like this…

``````void setup()
{
Serial.begin(115200);
Serial.println("Start psimeter 0.1");
}

void loop()
{
// MEASUREMENT
// make 16 readings and average them (reduces some noise) you can tune the number 16 of course
int count = 16;
int raw = 0;
for (int i=0; i< count; i++) raw += analogread(A0);  // return 0..1023 representing 0..5V
raw = raw / count;

// CONVERT TO VOLTAGE
float voltage = 5.0 * raw / 1023; // voltage = 0..5V;  we do the math in millivolts!!

// INTERPRET VOLTAGES
if (voltage < 0.5)
{
Serial.println("open circuit");
}
else if (voltage < 4.5)  // between 0.5 and 4.5 now...
{
float psi = mapFloat(voltage, 0.5, 4.5, 0.0, 15.0);    // variation on the Arduino map() function
Serial.print(millis());
Serial.print(", ");
Serial.println(psi, 3);  // 3 decimals
}
else
{
Serial.println("Signal too high!!");
}
}

float mapFloat(float x, float in_min, float in_max, float out_min, float out_max)
{
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}
``````