Weather station with ModBus over RS-485
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/*********************************************************************************
*
* weather_station is a weatherstation build around the SparkFun weather meter
* It can measure wind speed, wind gust , wind direction, rain fall, temperature,
* humidity and air pressure and has an RS-485 ModBus interface for your convenience.
*
* LED on Arduino gives status:
*
* ON : Booting
* BLINK : I2C ERROR
* FLASH : Heartbeat
*
* Copyright (C) 2023, 2024 M.T. Konstapel https://meezenest.nl/mees
*
* This file is part of weather_station
*
* weather_station is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* weather_station is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with weather_station. If not, see <https://www.gnu.org/licenses/>.
*
**********************************************************************************/
#include <ModbusSerial.h>
#include "SparkFun_Weather_Meter_Kit_Arduino_Library.h"
//I2C
#include <Wire.h>
#include "i2c.h"
//Temperature and humidity sensor
#include "i2c_SI7021.h"
SI7021 si7021;
// Pressure sensor
#include "i2c_BMP280.h"
BMP280 bmp280;
float PRESSURE_OFFSET = 210; // Calibration of BMP280: offset in Pascal
/**************************/
/* Configurable variables */
/**************************/
// Sparkfun weather station
int windDirectionPin = A0;
int windSpeedPin = 2;
int rainfallPin = 3;
// RS485 driver
#define RS485_RE 11 // Tight to RS485_DE and must be configured as an input to prevent a short circuit
#define RS485_DE 12
// Used Pins
const int TxenPin = RS485_DE; // -1 disables the feature, change that if you are using an RS485 driver, this pin would be connected to the DE and /RE pins of the driver.
// ModBus address
const byte SlaveId = 14;
/* Modbus Registers Offsets (0-9999)
*
* 30000: Weater station ID (0x5758)
* 30001: Wind direction (degrees)
* 30002: Wind speed (average over 10 minutes in km/h)
* 30003: Wind gust (peak wind speed in the last 10 minutes in km/h)
* 30004: Temperature (degrees Celcius)
* 30005: Rain last hour (l/m2)
* 30006: Rain last 24 hours (l/m2)
* 30007: Rain since midnight (l/m2) [NOT IMPLEMENTED, always 0]
* 30008: Humidity (percent)
* 30009: Barometric pressure (hPa)
* 30010: Luminosity (W/m2)
* 30011: Snow fall [NOT IMPLEMENTED, always 0]
* 30012: Raw rainfall counter (mm)
* 30013: Temperature pressure sensor (degrees Celsius)
* 30014: Status bits 0=heater, 1-15: reserved
*
*/
const int SensorIDIreg = 0;
const int SensorWindDirectionIreg = 1;
const int SensorWindSpeedIreg = 2;
const int SensorWindGustIreg = 3;
const int SensorTemperatureIreg = 4;
const int SensorRainIreg = 5;
const int SensorRainLast24Ireg = 6;
const int SensorRainSinceMidnightIreg = 7;
const int SensorHumidityIreg = 8;
const int SensorPressureIreg = 9;
const int SensorLuminosityIreg = 10;
const int SensorSnowFallIreg = 11;
const int SensorRainfallRawIreg = 12;
const int SensorTemperatureBackupIreg = 13;
const int SensorStatusBitsIreg = 14;
/* Modbus Registers Offsets (0-9999)
* Coils
* 0 = Heater algorithm (0 = disable, 1 = enable)
*/
const int HeaterCoil = 0;
// RS-485 serial port
#define MySerial Serial // define serial port used, Serial most of the time, or Serial1, Serial2 ... if available
const unsigned long Baudrate = 9600;
/******************************/
/* END Configurable variables */
/******************************/
// Create an instance of the weather meter kit
SFEWeatherMeterKit weatherMeterKit(windDirectionPin, windSpeedPin, rainfallPin);
// ModbusSerial object
ModbusSerial mb (MySerial, SlaveId, TxenPin);
unsigned long ts;
unsigned long HourTimer;
int WindGustData1[30];
unsigned char WindGustData1Counter=0;
int WindGustData2[10];
unsigned char WindGustData2Counter=0;
int WindAverageData1[30];
unsigned char WindAverageData1Counter=0;
int WindAverageData2[10];
unsigned char WindAverageData2Counter=0;
int RainPerHour[24];
unsigned char RainPerHourCounter=0;
struct MeasuredData {
int WindDirection;
int WindSpeed;
int WindGust;
int Rain;
int RainLast24;
int SensorRainSinceMidnight;
int Pressure;
int Luminosity;
int StatusBits = 0;
unsigned int RainfallCounter = 0;
float Temperature;
float Humidity;
float TemperatureBackup;
bool HeaterStatus = 0;
} MeasuredData;
// State machine implementing smart heater to prevent saturation of the sensor
char HeaterSi7021 (float humidity)
{
static int state=0;
static unsigned long StatemachineTimer=0;
bool TempValid=1;
bool Heater=0;
// If Smart heater algorithm is disabled, reset the statemachine forever.
// TempValid bit is also forced to 1, but it could be that we just came out of a heater period.
// We assume that the client on the other side of the ModBus is smart enough to understand.
if (MeasuredData.StatusBits & 0x04)
state = 0;
switch (state)
{
// Default state: humidity is below 95%
case 0:
Heater = 0;
if (humidity >= 95) {
StatemachineTimer = millis();
state = 1;
}
break;
// Humidity went above 95%. See if humidity stays above 95% for more than an hour, if so turn on heater
case 1:
if (humidity >= 95) {
if ( (millis() - StatemachineTimer) >= 3.6e+6 ) {
Heater = 1;
TempValid = 0;
StatemachineTimer = millis();
state = 2;
} else {
Heater = 0;
}
} else {
Heater = 0;
state = 0;
}
break;
// Heater is now on, let the sensor cook for 10 minutes
case 2:
if ( (millis() - StatemachineTimer) >= 600000 ) {
StatemachineTimer = millis();
Heater = 0;
state = 3;
} else {
Heater = 1;
}
TempValid = 0;
break;
// Heater is now off, let the sensor cool for 10 minutes
case 3:
if ( (millis() - StatemachineTimer) >= 600000 ) {
TempValid = 1; // Sensor cooled, so we can take a valid temperature reading
if (humidity >= 95) {
// Humidity still above 95%, repeat heating/cooling
Heater = 1;
StatemachineTimer = millis();
state = 2;
} else {
// Humidity below 95%, reset statemachine
Heater = 0;
state = 0;
}
} else {
Heater = 0;
TempValid = 0;
}
break;
default:
Heater = 0;
state = 0;
break;
}
return TempValid<<1 | Heater;
}
// Read Si7021 sensor and process data
void ReadSi7021 (void)
{
char result=0x2;
si7021.triggerMeasurement();
si7021.getHumidity(MeasuredData.Humidity);
if (MeasuredData.Humidity>100 || MeasuredData.Humidity<0)
MeasuredData.Humidity = 100;
//If humidity is larger than 95% switch on heater to get more acurate measurement and prevent memory offset
result = HeaterSi7021(MeasuredData.Humidity);
MeasuredData.StatusBits &= 0xFFFC; // Reset heater status bits to zero
MeasuredData.StatusBits |= result; // And set the proper bits to one if there are any. The result is we copied the status bits to the register
// Scale for more decimal positions when converted to integer value for ModBus
MeasuredData.Humidity *= 100;
// Temperture readings are valid (as the sensor is not heated)
if (result & 0x2) {
si7021.getTemperature(MeasuredData.Temperature);
// Scale for more decimal positions when converted to integer value for ModBus
MeasuredData.Temperature *= 100;
//Serial.print(F("Valid temp"));
}
// Statemachine thinks it is time to switch on the heater
if (result & 0x1) {
//Serial.print(F("Heater on."));
MeasuredData.HeaterStatus = 1;
} else {
//Serial.print(F("Heater off."));
MeasuredData.HeaterStatus = 0;
}
si7021.setHeater(MeasuredData.HeaterStatus);
}
// Read BMP280
void ReadBMP280 (void)
{
bmp280.awaitMeasurement();
float pascal;
bmp280.getPressure(pascal);
pascal = (pascal - PRESSURE_OFFSET) / 10; // Convert to hPa
MeasuredData.Pressure = pascal;
bmp280.getTemperature(MeasuredData.TemperatureBackup);
// Scale for more decimal positions when converted to integer value for ModBus
MeasuredData.TemperatureBackup *= 100;
bmp280.triggerMeasurement();
}
int MaxOfArray (int array[], unsigned int length)
{
int maximum_value = 0;
while (length--)
{
if (array[length] > maximum_value)
maximum_value = array[length];
}
return maximum_value;
}
int AverageOfArray (int array[], unsigned int length)
{
int tmp_value = 0;
unsigned char tmp_length = length;
int average_value = 0;
while (length--)
{
tmp_value += array[length];
}
average_value = tmp_value/tmp_length;
return average_value;
}
// Call this function every 2 seconds
void ReadSparkfunWeatherStation (void)
{
unsigned char cnt=0;
float tmpRegister;
tmpRegister = 10*weatherMeterKit.getWindDirection(); // Use float for conversion to degrees times 10, than put it in integer register for ModBus
MeasuredData.WindDirection = tmpRegister;
tmpRegister = 100*(weatherMeterKit.getWindSpeed())/3.6; // Use float for conversion to m/s times 100, than put it in integer register for ModBus
MeasuredData.WindSpeed = tmpRegister;
tmpRegister = 100*weatherMeterKit.getTotalRainfall(); // Use float for conversion to l/m2 times 100, than put it in integer register for ModBus
MeasuredData.Rain = tmpRegister;
// FIFO for calculating wind gust of last 10 minutes
// to preserve valuable RAM we caanot store all measurements of the last 10 minutes.
// So we use a hack: store the last 30 values in a FIFO and every minute we store the maximum value from this FIFO in another FIFO.
// This second FIFO is 10 deep: it stores the maximum values of the last 10 minutes.
// The maximum value from this FIFO is the maximum wind gust of the last 10 minutes.
if ( WindGustData1Counter < 29 )
{
WindGustData1Counter++;
}
else
{
if ( WindGustData2Counter < 9 )
{
WindGustData2Counter++;
}
else
{
WindGustData2Counter=0;
}
WindGustData2[WindGustData2Counter] = MaxOfArray(WindGustData1, 30);
WindGustData1Counter=0;
}
WindGustData1[WindGustData1Counter] = MeasuredData.WindSpeed;
MeasuredData.WindGust= MaxOfArray(WindGustData2, 10);
// Smart FIFO, same as for Wind Gust, but now for average wind speed over 10 minutes
if ( WindAverageData1Counter < 29 )
{
WindAverageData1Counter++;
}
else
{
if ( WindAverageData2Counter < 9 )
{
WindAverageData2Counter++;
}
else
{
WindAverageData2Counter=0;
}
WindAverageData2[WindAverageData2Counter] = AverageOfArray(WindAverageData1, 30);
WindAverageData1Counter=0;
WindAverageData1[WindAverageData1Counter] = MeasuredData.WindSpeed;
}
WindAverageData1[WindAverageData1Counter] = MeasuredData.WindSpeed;
MeasuredData.WindSpeed = AverageOfArray(WindAverageData2, 10);
// Record rainfall in one hour, save last 24 readings in FIFO
if ( ( millis() - HourTimer) >= 3.6e+6) {
HourTimer = millis();
if ( RainPerHourCounter < 23 )
{
RainPerHourCounter++;
} else {
RainPerHourCounter=0;
}
RainPerHour[RainPerHourCounter] = MeasuredData.Rain;
// Every time before we reset the TotalRainCounter we add the amount to the RawRainCounter.
// This 16 bit register will eventually overflow, but 655.35mm of rain fall is a lot!
MeasuredData.RainfallCounter += MeasuredData.Rain; // We don't care about the rounding error due to the convertion from float to int
weatherMeterKit.resetTotalRainfall();
// Calculate rain fall in the last 24 hours
MeasuredData.RainLast24=0;
for (cnt=0; cnt<24;cnt++) {
MeasuredData.RainLast24 += RainPerHour[cnt];
}
}
MeasuredData.Rain = RainPerHour[RainPerHourCounter];
}
void setup() {
MySerial.begin (Baudrate); // works on all boards but the configuration is 8N1 which is incompatible with the MODBUS standard
// prefer the line below instead if possible
// MySerial.begin (Baudrate, MB_PARITY_EVEN);
// initialize digital pin LED_BUILTIN as an output and turn it on.
pinMode(LED_BUILTIN, OUTPUT);
digitalWrite(LED_BUILTIN, HIGH);
//Setup control lines for RS485 driver
pinMode(RS485_RE,INPUT); // In hardware connected to RS485_DE. Should be input to prevent a short circuit!
pinMode(RS485_DE,OUTPUT);
digitalWrite(RS485_DE,LOW);
mb.config (Baudrate);
mb.setAdditionalServerData ("TEMP_SENSOR"); // for Report Server ID function (0x11)
// Add SensorIreg registers - Use addIreg() for analog Inputs
mb.addIreg (SensorIDIreg);
mb.addIreg (SensorWindDirectionIreg);
mb.addIreg (SensorWindSpeedIreg);
mb.addIreg (SensorWindGustIreg);
mb.addIreg (SensorTemperatureIreg);
mb.addIreg (SensorRainIreg);
mb.addIreg (SensorRainLast24Ireg);
mb.addIreg (SensorRainSinceMidnightIreg);
mb.addIreg (SensorHumidityIreg);
mb.addIreg (SensorPressureIreg);
mb.addIreg (SensorLuminosityIreg);
mb.addIreg (SensorSnowFallIreg);
mb.addIreg (SensorRainfallRawIreg);
mb.addIreg (SensorTemperatureBackupIreg);
mb.addIreg (SensorStatusBitsIreg);
// Add HeaterCoil register
mb.addCoil (HeaterCoil);
// Set Weather station ID
mb.Ireg (SensorIDIreg, 0x5758);
// Set unused register to zero
mb.Ireg (SensorRainSinceMidnightIreg, 0);
mb.Ireg (SensorSnowFallIreg, 0);
Serial.println(F("Weather station v0.2.1"));
Serial.println(F("(C)2024 M.T. Konstapel"));
Serial.println(F("This project is free and open source"));
Serial.println(F("More details: https://meezenest.nl/mees/"));
//Initialize Si7021 sensor
Serial.print(F("Humidity sensor SI7021 "));
if (si7021.initialize())
Serial.println(F("found"));
else
{
Serial.println(F("missing"));
while(1) {
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
delay(500); // wait for half a second
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
delay(500);
}
}
// The standard library of the Si7021 sets the heater element to the default 3.1mA, but we want the full power
// We could alter the library, but than we break compatibility. So for this one time we do a raw-write to the
// heater register.
const uint8_t SI7021_I2C_ADDRESS =(0x40);
const uint8_t SI7021_CMD_WRITE_HEATER_CONTROL_REG =(0x51);
const uint8_t SI7021_HEATER_FULL_BLAST =(0x0F); // Set heater to 94mA
i2c.writeByte(SI7021_I2C_ADDRESS, SI7021_CMD_WRITE_HEATER_CONTROL_REG, SI7021_HEATER_FULL_BLAST);
// Initialize BMP280 pressure sensor
Serial.print(F("Pressure sensor BMP280 "));
if (bmp280.initialize())
Serial.println(F("found"));
else
{
Serial.println(F("missing"));
while(1) {
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
delay(500); // wait for half a second
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
delay(500);
}
}
// onetime-measure:
bmp280.setEnabled(0);
bmp280.triggerMeasurement();
// Expected ADC values have been defined for various platforms in the
// library, however your platform may not be included. This code will check
// if that's the case
#ifdef SFE_WMK_PLAFTORM_UNKNOWN
// The platform you're using hasn't been added to the library, so the
// expected ADC values have been calculated assuming a 10k pullup resistor
// and a perfectly linear 16-bit ADC. Your ADC likely has a different
// resolution, so you'll need to specify it here:
weatherMeterKit.setADCResolutionBits(10);
#endif
// Here we create a struct to hold all the calibration parameters
SFEWeatherMeterKitCalibrationParams calibrationParams = weatherMeterKit.getCalibrationParams();
// The wind vane has 8 switches, but 2 could close at the same time, which
// results in 16 possible positions. Each position has a resistor connected
// to GND, so this library assumes a voltage divider is created by adding
// another resistor to VCC. Some of the wind vane resistor values are
// fairly close to each other, meaning an accurate ADC is required. However
// some ADCs have a non-linear behavior that causes this measurement to be
// inaccurate. To account for this, the vane resistor values can be manually
// changed here to compensate for the non-linear behavior of the ADC
calibrationParams.vaneADCValues[WMK_ANGLE_0_0] = 943;
calibrationParams.vaneADCValues[WMK_ANGLE_22_5] = 828;
calibrationParams.vaneADCValues[WMK_ANGLE_45_0] = 885;
calibrationParams.vaneADCValues[WMK_ANGLE_67_5] = 702;
calibrationParams.vaneADCValues[WMK_ANGLE_90_0] = 785;
calibrationParams.vaneADCValues[WMK_ANGLE_112_5] = 404;
calibrationParams.vaneADCValues[WMK_ANGLE_135_0] = 460;
calibrationParams.vaneADCValues[WMK_ANGLE_157_5] = 82;
calibrationParams.vaneADCValues[WMK_ANGLE_180_0] = 91;
calibrationParams.vaneADCValues[WMK_ANGLE_202_5] = 64;
calibrationParams.vaneADCValues[WMK_ANGLE_225_0] = 185;
calibrationParams.vaneADCValues[WMK_ANGLE_247_5] = 125;
calibrationParams.vaneADCValues[WMK_ANGLE_270_0] = 285;
calibrationParams.vaneADCValues[WMK_ANGLE_292_5] = 242;
calibrationParams.vaneADCValues[WMK_ANGLE_315_0] = 628;
calibrationParams.vaneADCValues[WMK_ANGLE_337_5] = 598;
// The rainfall detector contains a small cup that collects rain water. When
// the cup fills, the water is dumped and the total rainfall is incremented
// by some value. This value defaults to 0.2794mm of rain per count, as
// specified by the datasheet
calibrationParams.mmPerRainfallCount = 0.2794;
// The rainfall detector switch can sometimes bounce, causing multiple extra
// triggers. This input is debounced by ignoring extra triggers within a
// time window, which defaults to 100ms
calibrationParams.minMillisPerRainfall = 100;
// The anemometer contains a switch that opens and closes as it spins. The
// rate at which the switch closes depends on the wind speed. The datasheet
// states that a wind of 2.4kph causes the switch to close once per second
calibrationParams.kphPerCountPerSec = 2.4;
// Because the anemometer generates discrete pulses as it rotates, it's not
// possible to measure the wind speed exactly at any point in time. A filter
// is implemented in the library that averages the wind speed over a certain
// time period, which defaults to 1 second. Longer intervals result in more
// accurate measurements, but cause delay in the measurement
calibrationParams.windSpeedMeasurementPeriodMillis = 1000;
// Now we can set all the calibration parameters at once
weatherMeterKit.setCalibrationParams(calibrationParams);
// Begin weather meter kit
weatherMeterKit.begin();
ts = millis();
RainPerHourCounter = ts;
}
void loop() {
// Call once inside loop() - all magic here
mb.task();
// Read each two seconds
if ( ( millis() - ts) >= 2000) {
ts = millis();
digitalWrite(LED_BUILTIN, HIGH); // LED as heartbeat
// Read temperature and humidity
ReadSi7021();
// Read pressure and temperature
ReadBMP280();
// Read Wind and rain
ReadSparkfunWeatherStation();
// Setting Sparkfun weather station registers
mb.Ireg (SensorWindDirectionIreg, MeasuredData.WindDirection);
mb.Ireg (SensorWindSpeedIreg, MeasuredData.WindSpeed);
mb.Ireg (SensorWindGustIreg, MeasuredData.WindGust);
mb.Ireg (SensorRainIreg, MeasuredData.Rain);
mb.Ireg (SensorRainLast24Ireg, MeasuredData.RainLast24);
mb.Ireg (SensorTemperatureIreg, MeasuredData.Temperature);
mb.Ireg (SensorHumidityIreg, MeasuredData.Humidity);
mb.Ireg (SensorPressureIreg, MeasuredData.Pressure);
mb.Ireg (SensorTemperatureBackupIreg, MeasuredData.TemperatureBackup);
mb.Ireg (SensorLuminosityIreg, MeasuredData.Luminosity);
mb.Ireg (SensorRainfallRawIreg, MeasuredData.RainfallCounter);
mb.Ireg (SensorStatusBitsIreg, MeasuredData.StatusBits);
// Debug wind vane
//Serial.print(F("\n Measured ADC: "));
//Serial.print(analogRead(windDirectionPin));
// enable or disable smart heater
if (mb.Coil (HeaterCoil)) {
MeasuredData.StatusBits |= 0x04; // Set bit
} else {
MeasuredData.StatusBits &= 0x0B; // Reset bit
}
digitalWrite(LED_BUILTIN, LOW); // LED as heartbeat
}
}