Pressure Sensor Selection
I am eliminating MPS20N0040D as a pressure sensor possibility.It is only specified for dry non-corrosive gases and the sensitivity might be a problem ,it has no on-chip data conditioning and a stable difference amplifier is needed to amplify its analogue output. Its construction 4 resistors in a wheatstone bridge configuration. Trying out Bosch BMP280 temperature and pressure sensor which has SPI and I2C.
Beware there are knock-off breakout boards cloning Adafruit's superior breakout boards that advertise the superior Bosch BME280 temperature,pressure and humidity which actually have the inferior Bosch BMP280. See https://goughlui.com/2018/08/05/note-bosch-sensortec-bmp280-vs-bme280-sensor-confusion/
the BMP280 boards also have to have the Adafruit BMP280test example program in Arduino has to be changed to
/***************************************************************************
This is a library for the BMP280 humidity, temperature & pressure sensor
Designed specifically to work with the Adafruit BMP280 Breakout
----> http://www.adafruit.com/products/2651
These sensors use I2C or SPI to communicate, 2 or 4 pins are required
to interface.
Adafruit invests time and resources providing this open source code,
please support Adafruit andopen-source hardware by purchasing products
from Adafruit!
Written by Limor Fried & Kevin Townsend for Adafruit Industries.
BSD license, all text above must be included in any redistribution
***************************************************************************/
#include <Wire.h>
#include <SPI.h>
#include <Adafruit_BMP280.h>
#define BMP_SCK (13)
#define BMP_MISO (12)
#define BMP_MOSI (11)
#define BMP_CS (10)
Adafruit_BMP280 bmp; // I2C
//Adafruit_BMP280 bmp(BMP_CS); // hardware SPI
//Adafruit_BMP280 bmp(BMP_CS, BMP_MOSI, BMP_MISO, BMP_SCK);
void setup() {
Serial.begin(9600);
Serial.println(F("BMP280 test"));
if (!bmp.begin(0x76)) {
Serial.println(F("Could not find a valid BMP280 sensor, check wiring!"));
while (1);
}
/* Default settings from datasheet. */
bmp.setSampling(Adafruit_BMP280::MODE_NORMAL, /* Operating Mode. */
Adafruit_BMP280::SAMPLING_X2, /* Temp. oversampling */
Adafruit_BMP280::SAMPLING_X16, /* Pressure oversampling */
Adafruit_BMP280::FILTER_X16, /* Filtering. */
Adafruit_BMP280::STANDBY_MS_500); /* Standby time. */
}
void loop() {
Serial.print(F("Temperature = "));
Serial.print(bmp.readTemperature());
Serial.println(" *C");
Serial.print(F("Pressure = "));
Serial.print(bmp.readPressure());
Serial.println(" Pa");
Serial.print(F("Approx altitude = "));
Serial.print(bmp.readAltitude(1013.25)); /* Adjusted to local forecast! */
Serial.println(" m");
Serial.println();
delay(2000);
}
The line
if (!bmp.begin()) {
was changed to
if (!bmp.begin(0x76)) {
because these boards have a different default I2C address. The BMP280 datasheet
indicates that the BMP280 has 2 addresses implying 2 could be put on the same bus .
Beware there are knock-off breakout boards cloning Adafruit's superior breakout boards that advertise the superior Bosch BME280 temperature,pressure and humidity which actually have the inferior Bosch BMP280. See https://goughlui.com/2018/08/05/note-bosch-sensortec-bmp280-vs-bme280-sensor-confusion/
the BMP280 boards also have to have the Adafruit BMP280test example program in Arduino has to be changed to
/***************************************************************************
This is a library for the BMP280 humidity, temperature & pressure sensor
Designed specifically to work with the Adafruit BMP280 Breakout
----> http://www.adafruit.com/products/2651
These sensors use I2C or SPI to communicate, 2 or 4 pins are required
to interface.
Adafruit invests time and resources providing this open source code,
please support Adafruit andopen-source hardware by purchasing products
from Adafruit!
Written by Limor Fried & Kevin Townsend for Adafruit Industries.
BSD license, all text above must be included in any redistribution
***************************************************************************/
#include <Wire.h>
#include <SPI.h>
#include <Adafruit_BMP280.h>
#define BMP_SCK (13)
#define BMP_MISO (12)
#define BMP_MOSI (11)
#define BMP_CS (10)
Adafruit_BMP280 bmp; // I2C
//Adafruit_BMP280 bmp(BMP_CS); // hardware SPI
//Adafruit_BMP280 bmp(BMP_CS, BMP_MOSI, BMP_MISO, BMP_SCK);
void setup() {
Serial.begin(9600);
Serial.println(F("BMP280 test"));
if (!bmp.begin(0x76)) {
Serial.println(F("Could not find a valid BMP280 sensor, check wiring!"));
while (1);
}
/* Default settings from datasheet. */
bmp.setSampling(Adafruit_BMP280::MODE_NORMAL, /* Operating Mode. */
Adafruit_BMP280::SAMPLING_X2, /* Temp. oversampling */
Adafruit_BMP280::SAMPLING_X16, /* Pressure oversampling */
Adafruit_BMP280::FILTER_X16, /* Filtering. */
Adafruit_BMP280::STANDBY_MS_500); /* Standby time. */
}
void loop() {
Serial.print(F("Temperature = "));
Serial.print(bmp.readTemperature());
Serial.println(" *C");
Serial.print(F("Pressure = "));
Serial.print(bmp.readPressure());
Serial.println(" Pa");
Serial.print(F("Approx altitude = "));
Serial.print(bmp.readAltitude(1013.25)); /* Adjusted to local forecast! */
Serial.println(" m");
Serial.println();
delay(2000);
}
The line
if (!bmp.begin()) {
was changed to
if (!bmp.begin(0x76)) {
because these boards have a different default I2C address. The BMP280 datasheet
indicates that the BMP280 has 2 addresses implying 2 could be put on the same bus .
The 7-bit device address is 111011x. The 6 MSB bits are fixed. The last bit is changeable by SDO value and can be changed during operation. Connecting SDO to GND results in slave address 1110110(0x76); connection it to VDDIOresults in slave address 1110111(0x77)
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