Pressure tendency can forecast short-term changes in the weather. This is a very sophisticated device designed for sailors, yachtsmen, etc.

A barometer is a scientific instrument that is used to measure atmospheric pressure. Pressure tendency can forecast short-term changes in the weather.This time I will show you how to make an advanced barometer.

Inexpensive home weather stations only show images of raindrops, clouds or the sun. More advanced weather stations show the current pressure value as a number, and the pressure change over the preceding few hours as a rough bar graph, mainly for decorative purposes. Such weather stations are significantly more expensive. Also on the market, there are very sophisticated devices designed for sailors, yachtsmen, etc., with high accuracy showing both pressure changes and the current value, but such devices are very expensive. The device I present to you has all the features of such expensive barometers, but it is very simple to build and the price is many times lower. The original project is described on the website and I made some modifications to the code so that now the pressure values are displayed in Hectopascals, and there are also 3 LEDs to show the pressure trend.

It consists of only a few parts:

- Arduino Nano microcontroller

- BMP180 pressure sensor board, which is in direct contact with the surrounding air through this grille for more accurate temperature measurement

- LCD Display 16x2

- two resistors

- and four Leds

The measurement results are displayed on two lines. Immediately after turning on the barometer, the second line will be empty. Numerical values will appear there after 1 hour, 3 hours, and 10 hours, respectively. The first line displays the result of measuring the current atmospheric pressure in Hectopascals, next the deviation of the current pressure value from the average value for a given location, as well as the air temperature in degrees Celsius. The data shown in the top line is refreshed every 6 seconds, and this is displayed by a short flash of the white LED. The second line of the indicator displays the pressure increments over the last hour, three hours, and ten hours. If the pressure has increased during the specified time period, then the corresponding increment is displayed with a plus, otherwise - with a minus. The data in the second line is updated every 10 minutes. The three LEDs show the trend of Atmospheric pressure. If the pressure rises by more than 1.6 hectopascals in the last three hours, the yellow LED lights up (pressure rises). If the change is less than plus / minus 1.6 Hectopascals, the pressure is stable. And if the change is negative and greater than -1.6 hectopascals then we find that the pressure falling. These are quite a number of parameters based on which we can predict the local weather in the short term without using the Internet. Basically, the rising trend indicates a weather improvement, and a falling trend indicates a worsening. Standing pressure means stable weather.

Finally, the device is mounted in a suitable box made of PVC board and coated with self-adhesive wallpaper to get a professional look.

        #include <Wire.h>
#include <Adafruit_BMP085.h>
#include <LiquidCrystal.h>
LiquidCrystal lcd(2,3,4,5,6,7);
Adafruit_BMP085 bmp;

    const float mid_p = 1013.25; // Sea level atmospheric pressure
    int rLed = 10; // Rising Led
    int sLed = 11; // Steady Led
    int fLed = 12; //Falling Led
    int i;                    // For loop counter
    int j;                    // -------//---------
    long p;                   // Current pressure in Pa (1Pa = 0.0075006376 mmHg)
    long sum_p6;              // The sum of the results of pressure measurements for 6 sec.
    long mini_p6;             // Minimum pressure in 6 seconds
    long maxi_p6;             // Maximum pressure in 6 sec. 
    float  hg_p;              // Pressure in mmHg
    float dif_pm;             // Difference of pressure - current and average (mid_p) in mm Hg.
    float dif_p1;             // The difference in pressure - current and what was 1 hour ago
    float dif_p3;             // The difference in pressure - current and what was 3 hours ago
    float dif_p10;            // The difference in pressure - current and what was 10 hours ago
    boolean flag;             // Flag allowing to output dif_p1, dif_p3, dif_p10 with two additional spaces
    long sum_p[60];           // Array for storing 60 sums p. Each amount - 10,000 measurements in 10 minutes
    float t;                  // Current temperature in degrees C
    float sum_t6;             // The sum of the temperature measurement results in 6 seconds
    float mini_t6;            // Minimum temperature in 6 sec
    float maxi_t6;            // Maximum temperature in 6 sec
void setup() {
  pinMode (8, OUTPUT); // An LED is connected to D8 (11th leg) - a signaling device for the output of a new hg_P
  lcd.begin (16,2);
  for(i=0; i<60; i++)               // Zeroing the array sum_p [i]
  if (!bmp.begin()) {               // Pressure sensor defective
  lcd.print("BMP-180 DAMAGED!");
  while (1) {}                      // Loop
void loop() {
  sum_p[0] = 0;                     // In the for loop for j in sum_p [0] we will accumulate the sum of 10,000 measurements
  for (j=0;j<100;j++) {             // External cycle - we carry out 10,000 measurements in 600 seconds

    sum_p6=0;                       // Preparing data for the inner loop
    mini_p6=110000;                 // Knowingly more than possible
    maxi_p6= 80000;                 // Deliberately less than possible
    mini_t6=100.0;                  // Knowingly more than possible
    maxi_t6=0.0;                    // Deliberately less than possible 
      for(i=0;i<102;i++) {          // Internal loop - we carry out 102 measurements in 6 seconds
        if (p<mini_p6)              // Find the max and min results to discard later
        if (p>maxi_p6)
        sum_p6=sum_p6 + p;

        if (t<mini_t6)
        if (t>maxi_t6)
        sum_t6=sum_t6 + t;
        delay(18);                  // Adjusting the duration of the inner loop to 6 seconds
      }                             // finished an internal 6-second loop on i

    hg_p=1.0E-4 * (sum_p6-maxi_p6-mini_p6) + 77.32;  // 77.332 - Difference between Absolute, and Relative pressure for a given place        
    dif_pm=(hg_p - mid_p);
    digitalWrite (8,LOW);           // We turn on the LED - display a new result
    // We display the top line on the indicator - current pressure, deviation_
    // average pressure and temperature. 
    lcd.print (hg_p,1);
    lcd.print (" ");
    if (dif_pm >=0)                 // Знак "+" или "-" ставим сами
      lcd.print ("+");
      lcd.print ("-");
    lcd.print (abs (dif_pm),1);
    lcd.print (" ");
    if (abs(dif_pm)>=9.95){         // If dif_pm is long (5 familiar spaces), then t is displayed without tenths
      lcd.print (0.01*(sum_t6-maxi_t6-mini_t6),0);
      lcd.print (" ");              // Clearing the 16th digit
    else                            // Otherwise, we print t with tenths
    delay(83);                      // Adjusting the duration of the outer cycle to 10 minutes
    digitalWrite (8,HIGH);          // Turning off the LED
  }                                 // finished an outer 10-minute cycle on j

    dif_p1 = (sum_p[0] - sum_p[6]) * 1.0E-6; 
    dif_p3 = (sum_p[0] - sum_p[18])* 1.0E-6 ;
    dif_p10 = (sum_p[0] - sum_p[59])* 1.0E-6 ;
    flag=false;                     // no spaces can be inserted into the 2nd line
    if (abs(dif_p1)<9.95 and abs(dif_p3)<9.95 and abs(dif_p10)<9.95)
      flag=true;                    // If dif_p occupy 4 familiar spaces, then spaces can be inserted
    if (sum_p[59]==0)               // If there is no data for dif_p10 yet, then spaces can be inserted
  // We output dif_p1, dif_p3 and dif_p10 to the 2nd (bottom) line of the indicator

    lcd.setCursor (0,1);
    lcd.print ("                "); // Clearing the 2nd line
    lcd.setCursor (0,1);
  // Час назад...
    if (sum_p[6]>0) {               // If data collection started more than an hour ago
      if (dif_p1 >=0)               // We put the "+" or "-" sign ourselves
         lcd.print ("+");
         lcd.print ("-");     
      lcd.print (abs (dif_p1),1);
      lcd.print (" "); 
    else                            // No data yet ...
      lcd.print ("--.- ");

    if (flag==true)
      lcd.print (" ");

      // 3 Часа назад...
    if (sum_p[18]>0) {              // If data collection started more than 3 hours ago
      if (dif_p3 >=0)               // We put the "+" or "-" sign ourselves
         lcd.print ("+");
         lcd.print ("-");     
      lcd.print (abs (dif_p3),1);
      lcd.print (" "); 
    else                            // No data yet ...
      lcd.print ("--.- ");

    if (flag==true)
      lcd.print (" ");
      // 10 Часов назад... 
    if (sum_p[59]>0) {              // If data collection started more than 10 hours ago
      if (dif_p10>=0)               // We put the "+" or "-" sign ourselves
        lcd.print ("+");
        lcd.print ("-");     
      lcd.print (abs (dif_p10),1);
    else                            // No data yet ...
      lcd.print ("--.-");
    // Shift the contents of the sum_p [] array one position to the right
    sum_p[i] = sum_p[i-1];

    if (dif_p3 > 1.6) {
     digitalWrite(rLed, HIGH);
     digitalWrite(sLed, LOW);
     digitalWrite(fLed, LOW);
   if (dif_p3 < -1.6) {
     digitalWrite(rLed, LOW);
     digitalWrite(sLed, LOW);
     digitalWrite(fLed, HIGH);
   if (dif_p3 > -1.6 && dif_p3 < 1.6) {
     digitalWrite(rLed, LOW);
     digitalWrite(sLed, HIGH);
     digitalWrite(fLed, LOW);

// End of sketch
Mirko Pavleski
Electronics , Arduino , Physics