MS5540C Arduino Library

Brief sensor description

Given sensor operates using slightly modified SPI interface (the main difference is that sensor does not have SS/CS (Slave Select/Chip Select) line. Instead, this sensor receives 3 START and 3 STOP bits before and after each bit control sequence. It can operate up to 100m below water surface (as said in datasheet).

Code example

Here's a simple example which measures current temperature and pressure in mbars each 3 seconds. For further explanations on the comments read section "Explanations" below.

Also, if you don't know AVR MCU's like the back of your hand, please carefully read "Important notes" section to avoid different tricky problems.

#include <SPI.h>
#include <ms5540c.h>

ms5540c sensor;

void setup() {
    Serial.begin(9600);
    SPI.begin(); // Sensor doesn't start SPI communication itself so we're to enable it ourselves
    sensor.begin();
}

void loop() {
    const float temp = sensor.getTemperature();  // Temperature in degrees Celsius
    const float pressure = sensor.getPressure(); // pressure in mbar
    Serial.print("Temperature: ");
    Serial.print(temp);
    Serial.println(" C");
    Serial.print("Pressure: ");
    Serial.print(pressure);
    Serial.println(" mbar");
    Serial.print("          ");
    Serial.print(conv::mbarToAtm(pressure));
    Serial.println(" atm");
    Serial.print("          ");
    Serial.println(conv::mbarToPascal(pressure));
    Serial.println(" pas");
    Serial.println("\n=======================\n");

    delay(3000);
}

Important notes

Connection with MCU features

Library uses hardware implementation of SPI library, so refer to actual pinout diagram of your MCU to make sure which actual pins are reliable for MISO/MOSI/SCK lines.

Very important note: sensor lacks internal clock source so it is needed to provide external clock source. It is made via MCLK pin. Make sure you've connected this input to OC1A pin (refer to your actual MCU and Arduino pinout).

Handy tip: if you're using Arduino Uno R3, OC1A is attached to pin D9.

Connecting this input to some another pin will lead to sensor malfunctioning and you'll get strange and incorrect measurement results (like negative pressure, etc.).

Note: it's better to have pullup resistors on serial lines to get rid of noise.