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Topic: BMP180 Poor Precision (Read 151 times) previous topic - next topic

immured

Hello,

My BMP180 Barometer recently stopped being as Precise as It had been before. In a matter of 5 or so minutes, Inside, without being moved or touched, The Sensor will begin to get readings of 7-10 feet higher than its zero. This is a problem because there is no wind or airflow around it and it should remain at its zero if its not moving.

This is an example of the data Drift over a time of less than 5 minutes

Code: [Select]

Pressure,     Altitude (feet)
 1010.79059, 0.13
 1010.79465, 0.53
 1010.73731, -0.85
 1010.76329, -0.19
 1010.74102, 0.88
 1010.84560, 1.49     
 1010.85268, 1.28
 1010.81187, 0.72
 1010.83076, -1.48
 1010.82705, 0.61
 1010.83580, 0.27
 1010.75912, 0.33
 1010.74938, 2.59
 1010.78787, 0.51
 1010.71099, 1.33
 1010.80174, 1.20
 1010.71168, 1.41
 1010.78184, 1.54
 1010.74775, 3.44
 1010.73926, 1.33
 1010.75541, 1.04
 1010.72461, 0.30
 1010.69213, 2.61
 1010.78077, 2.07
 1010.72474, 4.38
 1010.72805, 3.06
 1010.69467, 3.68
 1010.64645, 4.70
 1010.64274, 4.13
 1010.68520, 2.45
 1010.67241, 5.10
 1010.66870, 3.82
 1010.69506, 3.46
 1010.68432, 3.50
 1010.63035, 4.31
 1010.64391, 7.16
 1010.62741, 4.65
 1010.62612, 5.45
 1010.64708, 5.44
 1010.66804, 3.33
 1010.67619, 3.05
 1010.58989, 6.49
 1010.66884, 5.00
 1010.50759, 6.51
 1010.64556, 4.61
 1010.55650, 7.10
 1010.59191, 5.06
 1010.61249, 5.82
 1010.60135, 5.76
 1010.51229, 7.70
 1010.56626, 7.08
 1010.55916, 4.94
 1010.59086, 7.02
 1010.53689, 7.01
 1010.52173, 7.44
 1010.57368, 8.17
 1010.60845, 4.71
 1010.57101, 6.55
 1010.58889, 5.75
 1010.55144, 7.55
 1010.59394, 6.99
 1010.55144, 6.37
 1010.54571, 5.04
 1010.59058, 6.68
 1010.58078, 6.48
 1010.53220, 8.48
 1010.55950, 6.92
 1010.59457, 6.05
 1010.65225, 4.89
 1010.65393, 5.40
 1010.62760, 4.29
 1010.57733, 6.79
 1010.60330, 8.68
 1010.54933, 5.61
 1010.57530, 7.10
 1010.59384, 5.57
 1010.55675, 5.00
 1010.53820, 6.52
 1010.66099, 5.11
 1010.61981, 5.72
 1010.64207, 4.55
 1010.54358, 6.08
 1010.64411, 5.82
 1010.59384, 5.67
 1010.59552, 6.89
 1010.64040, 5.00
 1010.66135, 4.68
 1010.56656, 5.28
 1010.60570, 3.46
 1010.60234, 6.77
 1010.49033, 6.01
 1010.52779, 9.41
 1010.58211, 5.13
 1010.59562, 6.74
 1010.66681, 6.27
 1010.42576, 10.67
 1010.48309, 10.03
 1010.35751, 11.96




This is the Code I am Using:

Code: [Select]
#include <TinyGPS.h>

#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include "RH_ASK.h"
#include "RH_RF95.h"
#include "SFE_BMP180.h"
#include "avr/dtostrf.h"

File main_folder; // initialize folder for saving
File dataFile; // initialize sd file
const int chipSelect = 10; // CS pin on sd card module
int prev_file_indx = 0; // used for file naming
String fileName = "000";
float baseline;


SFE_BMP180 bmp;
TinyGPS gps;

#define RFM95_CS 8
#define RFM95_RST 4
#define RFM95_INT 3
//#define Serial SERIAL_PORT_USBVIRTUAL
#define RF95_FREQ 433.0




// Singleton instance of the radio driver
RH_RF95 rf95(RFM95_CS, RFM95_INT);

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

  bool status;
  status = bmp.begin();
  if (!status) {

    while (1);
  }
  char startTemperature(void);
  delay(500);
      status = bmp.startPressure(3);
      if (status != 0)
      {
        // this will prevent drift and give a more precise measurement at "3"
      }
        // Wait for the measurement to complete:
        delay(status);

  baseline = (bmp.getPressure());

  

  Serial1.begin(9600);
  pinMode(8, OUTPUT);
  digitalWrite(8, HIGH);
  delay(1000);

  if (!SD.begin(chipSelect)) {
    Serial.println("SD not found ");
    return;
  }
  pinMode(8, OUTPUT);
  digitalWrite(8, LOW);
  delay(1000);

  pinMode(RFM95_RST, OUTPUT);
  digitalWrite(RFM95_RST, HIGH);


  // manual reset
  digitalWrite(RFM95_RST, LOW);
  delay(10);
  digitalWrite(RFM95_RST, HIGH);
  delay(10);

  while (!rf95.init()) {
    Serial.println("LoRa radio init failed");
    Serial.println("Uncomment '#define SERIAL_DEBUG' in RH_RF95.cpp for detailed debug info");
    while (1);
  }
  Serial.println("LoRa radio init OK!");

  // Defaults after init are 434.0MHz, modulation GFSK_Rb250Fd250, +13dbM
  if (!rf95.setFrequency(RF95_FREQ)) {
    Serial.println("setFrequency failed");
    while (1);
  }
  Serial.print("Set Freq to: "); Serial.println(RF95_FREQ);
  
  rf95.setTxPower(23, false);
  //Leave False NO RFO on Feather
  rf95.setModemConfig(RH_RF95::Bw31_25Cr48Sf512);
  main_folder = SD.open("/");
  fileName = sd_saver(main_folder);
}

int16_t packetnum = 0;  // packet counter, we increment per xmission

void loop()
{
  float flat, flon, alt;
  unsigned long age, date, time, chars = 0;
  unsigned short sentences = 0, failed = 0;
  int year;
  byte month, day, hour, minute, second, hundredths;

  Serial1.begin(9600);
  pinMode(8, OUTPUT);
  digitalWrite(8, HIGH);
  delay(1000);

  gps.crack_datetime(&year, &month, &day, &hour, &minute, &second, &hundredths);
  gps.f_get_position(&flat, &flon, &age);

  char sz[32];
  sprintf(sz, "%02d/%02d/%02d %02d:%02d:%02d",
          month, day, year, hour - 4, minute, second);
  Serial.print(sz);
  Serial.print(", ");
  Serial.print(flat, 6);
  Serial.print(", ");
  Serial.print(flon, 6);
  Serial.print(", ");
  Serial.print(bmp.getPressure(), 5);
  delay(260);
  Serial.print(", ");
  Serial.println(bmp.altitude() * 3.28084, 2);//altitude in feet 2 decimal places
  smartdelay(2000);
  
  dataFile = SD.open("DATA" + fileName + ".txt", FILE_WRITE);
  if (dataFile) {
    dataFile.print(sz);
    dataFile.print(", ");
    dataFile.print(flat, 6);
    dataFile.print(", ");
    dataFile.print(flon, 6);
    dataFile.print(", ");
    dataFile.print(bmp.getPressure(), 5);
    dataFile.print(", ");
    dataFile.println(bmp.altitude() * 3.28084, 2); //altitude in feet 2 decimal places
    dataFile.close();
  }
  else {
    Serial.println("Not Writing");
  }
  pinMode(8, OUTPUT);
  digitalWrite(8, LOW);
  delay(1000);

  char dataPKG [RH_RF95_MAX_MESSAGE_LEN];

  sprintf (dataPKG, "%f, %f, %f, %f", flat, flon, (bmp.getPressure()), baseline);

  Serial.println (dataPKG);

  Serial.println("Transmitting..."); // Send a message to rf95_server

  dataPKG[69] = 0;

  Serial.println("Sending...");
  delay(10);
  rf95.waitPacketSent();
  rf95.send((uint8_t *)dataPKG, 70);
  uint8_t buf[RH_RF95_MAX_MESSAGE_LEN];
  uint8_t len = sizeof(buf);

  Serial.println("Waiting for reply...");
  if (rf95.waitAvailableTimeout(3000))
  {
    // Should be a reply message for us now  
    if (rf95.recv(buf, &len))
   {
      Serial.print("Got reply: ");
      Serial.println((char*)buf);
      Serial.print("RSSI: ");
      Serial.println(rf95.lastRssi(), DEC);    
    }
    else
    {
      Serial.println("Receive failed");
    }
  }
  else
  {
    Serial.println("No reply, is there a listener around?");
  }

}

String sd_saver(File dir) {
  while (true) {
    // iterate all files to ensure no overwrites
    File entry = dir.openNextFile();
    if (!entry) {
      break;
    }
    // naming routine
    String entry_name = entry.name();
    if ((entry_name.substring(4, 7)).toInt() >= prev_file_indx) {
      prev_file_indx = (entry_name.substring(4, 7)).toInt() + 1;
      if (prev_file_indx >= 100) {
        fileName = String(prev_file_indx);
      } else if (prev_file_indx >= 10) {
        fileName = "0" + String(prev_file_indx);
      } else {
        fileName = "00" + String(prev_file_indx);
      }

    }
    entry.close();

  }
  return fileName;
}


Any insight as to where I am going wrong is greatly appreciated. Thank you

srnet

#1
Aug 20, 2019, 06:28 pm Last Edit: Aug 20, 2019, 06:32 pm by srnet
So your sensor used to be 'OK' and now its not.

If you have not changed the code, the connecting hardware or environment then perhaps the sensor is faulty.

Did you try a replacement sensor, how did that behave ?
http://www.50dollarsat.info/
http://www.loratracker.uk/

hammy

Is it connected to 3.3v ?

immured

It is connected to 3.3v. I only Noticed the drift recently. I did have to change the code when I switched over to an Adafruit Feather but for the first week I had It working I did not notice any sort of drift over such a short period of time.

jremington

#4
Aug 20, 2019, 08:42 pm Last Edit: Aug 20, 2019, 09:46 pm by jremington
Those small changes could be due to genuine variations in the atmospheric pressure, a battery going dead, etc.

immured

Also I am not sure if this makes a difference but I just realized that I am also Not getting and initialization messages in my serial monitor from the barometer. I am only getting them from the LoRa Radio.

srnet

Was the problem the same with the replacement sensor ????????
http://www.50dollarsat.info/
http://www.loratracker.uk/

MarkT

Sounds like temperature drift - shouldn't the sensor be in sleep mode most of the time - perhaps this has changed for some reason, leading to self-heating?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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