Hello!
I have a Nano setup with a BME280. It is stored in a box with other electronics that generates heat after a while of being on so it messes up my reading. The temperature will rise. I want to read and store the Temp when it is first tuned on so it can display just that temp reading. How can I do this after a few seconds of being turned on?
Thanks,
Kevin
Read the sensor a few seconds after reboot, and store the value in a global variable.
If you need a more precise answer, post more of your code.
If the temperature in the BME280 enclosure is higher than the ambient temperature, the pressure measurements will probably be wrong, too.
jremington:
If the temperature in the BME280 enclosure is higher than the ambient temperature, the pressure measurements will probably be wrong, too.
Doesn't the code automatically compensate for temperature changes?
No it doesnt compensate for the temp changes.
I am not sure how to store the value in a global value and to store it after a set time. Kinda beyond my programming abilities , I am learning all of this and putting peices of code together for this project.
The code is setup to calculate air density(rho) and relative air density while also being able to read external air pressure with a pressure sensor.
#include "U8glib.h" //LCD 128x64 ST7920 Display Library
#include "SparkFunBME280.h" // BME280 Library
#include "Wire.h" // I2C Library For Sensor
// Flow Meter Set Integers Start
//int rawValue; // A/D readings
int offset = 44; // zero flow pressure adjust (~30-72)
int fullScale = 819; // max pressure adjust (~798-840)
float flowpressure; // final pressure in mmHg
int battery;
int pressurezero;
uint32_t rawValue; // new average code
int rawAccumulator; // new average code
int filteredValue; // new average code
// Flow Meter Set Integers End
// Weather Integers Start
BME280 Sensor;
float kelvin = 0;
float dewptk = 0;
float dewptc = 0;
float dewptf = 0;
float baromb; //pressure millibar
float baropascal; //pressure in Pascals
float gconstdry = 287.058; //gas constant for dry air
float gconstwaterv = 461.495; //gas constant, water vapor
double psatmb; //pressure saturated millibar
double psatnum; //pressure saturated numerator
double psatden; //pressure saturated denominator
double psatfract; //pressure saturated fraction
double psatexpo; //exponent for pressure saturated
double pvapwater; //pressure, water vapor component
double pdryair; //pressure, dry air
double psatpascals; //pressure saturated in Pascals
double phumidA; //part A of equation
double phumidB; //part B of equation
double rho; //variable for air density in Kg/m3
int analogPin = 2; //
int val = 0; //initialize value to 0
float pottopress; //from (pot*0.0017578)+29.92
float pressalt; //from (SLP -Baro) *994
float degc;
float degf;
float pressure;
float h;
float inhg;
double rad; // relative air density(rad) = 100 * (current air density) / (reference air density) standard automotive reference 1.1568 kg/m3
// Weather Integers End
// constructor call for display
U8GLIB_ST7920_128X64 u8g(13, 11, 10, U8G_PIN_NONE); // SPI Com: SCK = en = 13, MOSI = rw = 11, CS = di = 0
void draw(void)
{
// graphic commands to redraw the complete screen should be placed here
}
void setup(void)
{
u8g.setRot180(); // flip screen / rotated for current display
// set SPI backup if required / not required with current display
//u8g.setHardwareBackup(u8g_backup_avr_spi);
//***Set up sensor******************************//
//commInterface I2C_MODE
Sensor.settings.commInterface = I2C_MODE;
Sensor.settings.I2CAddress = 0x76;
Sensor.settings.runMode = 3; // 3, Normal mode
Sensor.settings.tStandby = 0; // 0, 0.5ms
Sensor.settings.filter = 0; // 0, filter off
//tempOverSample can be:
// 0, skipped
// 1 through 5, oversampling *1, *2, *4, *8, *16 respectively
Sensor.settings.tempOverSample = 1;
//pressOverSample can be:
// 0, skipped
// 1 through 5, oversampling *1, *2, *4, *8, *16 respectively
Sensor.settings.pressOverSample = 1;
//humidOverSample can be:
// 0, skipped
// 1 through 5, oversampling *1, *2, *4, *8, *16 respectively
Sensor.settings.humidOverSample = 1;
//***Initialize Sensor**************************//
Serial.begin(57600);
Serial.print("Program Started\n");
Serial.println("Starting BME280... result of .begin():");
delay(10); //Make sure sensor had enough time to turn on. BME280 requires 2ms to start up.
//Calling .begin() causes the settings to be loaded
Serial.print("Sensor: 0x");
Serial.println(Sensor.begin(), HEX);
}
void loop(void)
{
//pressurezero = analogRead(A2) / 8;
rawValue = analogRead(A0);
flowpressure = (filteredValue - offset) * 650.0 / (fullScale - offset); // offset or pressurezero for trimmer pot Replaced rawValue with filteredValue. 650.0 for calibrated pressure conversion
battery = analogRead(A1)/8.9; // Display battery percentage at max 100%
if (flowpressure < 0) // If pressure is below zero have display show zero
{
flowpressure = 0;
}
if (battery > 100) // If battery tries to display over 100% have display show 100%
{
battery = 100;
}
// New code for averaging - On each pass, it subtracts 1/8 of the total rawAccumulator value, then adds in the current rawValue.
// So over time, the rawAccumulator value will converge on 8x the average raw value.
// Then it takes 1/8 of the rawAccumulator value as the filteredValue.
rawAccumulator -= (rawAccumulator >> 2); // new average code. Can change 3 to 2 for less or 3 to 4 for more averaging.
rawAccumulator += rawValue; // new average code
filteredValue = rawAccumulator >> 2; // new average code. Can change 3 to 2 for less or 3 to 4 for more averaging.
val = analogRead(analogPin);
pottopress = (val * 0.0017578) + 29.92; //"Kollsman Window" value calculation
//Start with temperature, as that data is needed for accurate compensation.
//Reading the temperature updates the compensators of the other functions
//in the background.
//float degf = Sensor.readTempF() - 3.4; // read and calibrate temp f
float degc = Sensor.readTempC() - 5.0; // read and calibrate temp c & temp f
degf = (degc * 1.8) + 32;
float h = Sensor.readFloatHumidity() - 2; // read and calibrate humidity
float pressure = Sensor.readFloatPressure();
inhg = pressure / 3386;
baromb = inhg * 33.86;
baropascal = inhg * 3386;
kelvin = degc + 273.15;
dewptk = kelvin - ((100 - h) / 5);
dewptc = dewptk - 273.15;
dewptf = ((dewptc * 1.8) + 32);
pressalt = (pottopress - inhg) * 994; //calculate feet
psatnum = 7.5 * degc; //calculate the numerator of the psat exponent
psatfract = psatnum / psatden; //calculate the psat exponent fraction
psatden = degc + 237.3; //calculate the denominator of the psat exponent psatfract = psatnum psatden; //calculate the psat exponent fraction
psatexpo = pow(10, psatfract); //calculate exponent for psat
psatmb = 6.1087 * psatexpo; //calculate psat in millibars
psatpascals = psatmb * 100; //convert psat millibars (hectopascals) to pascals
pvapwater = (h / 100 * psatmb) * 100; //calculate water vapor pressure component
pdryair = baropascal - pvapwater; //calculate partial pressure dry air component
phumidB = pdryair / (gconstdry * kelvin); //part B of the pressure humid air calculation
phumidA = pvapwater / (gconstwaterv * kelvin); //part A of humid air pressure
rho = phumidA + phumidB; //calculate RHO in Kg/m3!
rad = (rho / 1.225) * 100;
// picture loop
u8g.firstPage();
do
{
draw();
if (millis() < 5000) // It's been less than 5 seconds since reset
{
u8g.setFont(u8g_font_fub30r); //Set font
u8g.drawStr( 20, 32, "K&D");
u8g.setFont(u8g_font_unifontr); //Set Font
u8g.drawStr( 18, 43, "InnoVations");
u8g.drawStr( 0, 64, "Go With The Flow");
}
else if (battery > 80)
{
u8g.setFont(u8g_font_unifontr); //Set font
u8g.drawStr( 0, 10, "FLOW");
u8g.drawStr( 80, 10, "TEMP'F");
u8g.setPrintPos(85, 22);
u8g.print(degf, 1);
//u8g.drawStr( 100, 22, "'F");
u8g.drawStr( 80, 37, "RAD %");
u8g.setPrintPos(85, 50);
u8g.print(rad, 1);
//u8g.drawStr( 105, 50, "%");
u8g.setFont(u8g_font_fub30r); //Set font
u8g.setPrintPos(0, 48);
u8g.print(flowpressure, 0);
u8g.setFont(u8g_font_unifontr); //Set font
u8g.drawStr( 18, 64, "BATTERY %");
u8g.setPrintPos(89, 64);
u8g.print(battery);
}
else
{
u8g.setFont(u8g_font_unifontr); //Set font
u8g.drawStr( 7, 38, "CHARGE BATTERY");
}
}
while ( u8g.nextPage() );
// rebuild the picture after some delay
delay(200);
}
I really don't understand your problem - in your setup function, after you have initialised the sensor, put a simple delay (2000), then do a read from the BME280. Put the result in a global variable.
Or is my solution too simplistic? Have I missed something?
I understand what you mean, but don't know how to go about doing it. I have never worked with coding that before. I am still pretty much a newbie! I need to see some example code.
There's a load of fairly complex example code in reply 4 - where did that come from?
The BME280 object is called Sensor, so it should be easy to figure out how values are read (though why anyone would choose to work in Fahrenheit is beyond me).
It's not in Fahrenheit, it calculates from celcius and kelvin. I then calculate Fahrenheit off of celcius. The calculations all come from a website call Shelquest Engineering. Other code has been posted on Arduino Forum that I used and put in. I have another friend that has helped me with converting the old code for old sensor to the new BME280. I have worked on this for a few months.
The sensor uses its own temperature to calculate the air pressure from the internal readings.
Have you checked whether the pressure readings change unreasonably as the enclosure heats up?
Yes I have and it effects all reading since they are calculated off of temp, humidity and barometric pressure.
How much will the sensor warm on it's own once powered on?
I don't understand why it doesn't read room temperature correctly either. If I calibrate it or do a offset then take it outside it reads high. Maybe the sensor is bad because it is not linear. That's probably whats going on that the sensor is not a good one.
How much will the sensor warm on it's own once powered on?
Self heatiing is not significant if the sensor is mounted on a PCB with decent airflow, which is required in any case for proper environmental monitoring.
I suggest to take the sensor out of the box.