This is a new mini weather station that I have been working on.
It provides Temperature, Humidity, Pressure, and Battery Voltage.
The case is designed to be printed without the need for any support, has vents in the front and sides. The front slides on to make it easy to replace the 9v battery. It is designed to take a 50x70mm prototype board. This gives heaps of room for the sensors.
The 3d files can be found on http://www.thingiverse.com/thing:704715
The code is mostly a refactor from the examples in the MySensors libraries, with a simplification of the forecast algorithm to reduce the amount of memory that it uses.
#include <SPI.h>
#include <MySensor.h>
#include <DHT.h>
#include <Wire.h>
#include <Adafruit_BMP085.h>
#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1
#define CHILD_ID_BARO 2
#define CHILD_ID_BARO_TEMP 3
#define HUMIDITY_SENSOR_DIGITAL_PIN 3
int BATTERY_SENSE_PIN = A0; // select the input pin for the battery sense point
#define SLEEP_MINUTE 60000
#define SLEEP_FIVE_MINUTES 300000
MySensor gw;
DHT dht;
Adafruit_BMP085 bmp = Adafruit_BMP085(); // Digital Pressure Sensor
float lastTemp = -1.0;
float lastHum = -1.0;
float lastBaroTemp = -1.0;
int lastForecast = -1;
char *weather[] = { "Stable", "Sunny", "Cloudy", "Unstable", "Thunderstorm", "Unknown" };
int minutes;
int pressureSamples[5];
float lastPressureAvg = -1.0;
int lastPressure = -1;
int minuteCount = 0;
float pressureAvg;
int pressure;
float dP_dt;
boolean metric = true;
MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
MyMessage msgBaroTemp(CHILD_ID_BARO_TEMP, V_TEMP);
MyMessage msgBaro(CHILD_ID_BARO, V_PRESSURE);
MyMessage msgForecast(CHILD_ID_BARO, V_FORECAST);
void setup() {
// use the 1.1 V internal reference
analogReference(INTERNAL);
gw.begin();
dht.setup(HUMIDITY_SENSOR_DIGITAL_PIN);
if (!bmp.begin()) {
Serial.println("Could not find a valid BMP085 sensor, check wiring!");
}
// Send the Sketch Version Information to the Gateway
gw.sendSketchInfo("Mini Weather Station", "3.2");
// Register all sensors to gw (they will be created as child devices)
gw.present(CHILD_ID_HUM, S_HUM);
gw.present(CHILD_ID_TEMP, S_TEMP);
gw.present(CHILD_ID_BARO, S_BARO);
gw.present(CHILD_ID_BARO_TEMP, S_TEMP);
metric = gw.getConfig().isMetric;
}
void loop() {
Serial.print("minuteCount = ");
Serial.println(minuteCount);
// The pressure Sensor Stuff
int forecast = SamplePressure();
if ( minuteCount > 4 ) { // only every 5 minutes
// Process the barometric sensor data
float baro_temperature = bmp.readTemperature();
if (!metric) { // Convert to fahrenheit
baro_temperature = baro_temperature * 9.0 / 5.0 + 32.0;
}
if (baro_temperature != lastBaroTemp) {
gw.send(msgBaroTemp.set(baro_temperature, 1));
lastBaroTemp = baro_temperature;
}
if (pressure != lastPressure) {
gw.send(msgBaro.set(pressure, 0));
//delay(1000);
// gw.send(msgBaro.set(pressure));
lastPressure = pressure;
}
if (forecast != lastForecast) {
gw.send(msgForecast.set(weather[forecast]));
lastForecast = forecast;
}
// The humidity sensor stuff
delay(dht.getMinimumSamplingPeriod());
float temperature = dht.getTemperature();
if (isnan(temperature)) {
Serial.println("Failed reading temperature from DHT");
} else if (temperature != lastTemp) {
lastTemp = temperature;
if (!metric) {
temperature = dht.toFahrenheit(temperature);
}
gw.send(msgTemp.set(temperature, 1));
Serial.print("Temperature: ");
Serial.println(temperature);
}
float humidity = dht.getHumidity();
if (isnan(humidity)) {
Serial.println("Failed reading humidity from DHT");
} else if (humidity != lastHum) {
lastHum = humidity;
gw.send(msgHum.set(humidity, 1));
Serial.print("Humidity: ");
Serial.println(humidity);
}
// get the battery Voltage
long sensorValue = analogRead(BATTERY_SENSE_PIN);
// 1M, 100K divider across battery and using internal ADC ref of 1.1V
// Sense point is bypassed with 0.1 uF cap to reduce noise at that point
// ((1e6+100e3)/100e3)*1.1 = Vmax = 12.1 Volts
// 12.1/1023 = Volts per bit = 0.011827957
// sensor val at 9v = 9/0.011827957 = 760.909090217
// float batteryV = sensorValue * 0.011827957;
long batteryValue = sensorValue * 100L;
int batteryPcnt = batteryValue / 761;
gw.sendBatteryLevel((batteryPcnt > 100 ? 100 : batteryPcnt)); // this allows for batteries that have slightly over 9v
Serial.print("Batt %:");
Serial.println(batteryPcnt);
}
if ( minuteCount < 5 ) // sleep a bit
gw.sleep(SLEEP_MINUTE); //while pressure sampling
else
gw.sleep(SLEEP_FIVE_MINUTES);
}
int SamplePressure() {
// This is a simplification of Algorithm found here to same memory
// http://www.freescale.com/files/sensors/doc/app_note/AN3914.pdf
pressure = bmp.readSealevelPressure(60) / 100; // 60 meters above sealevel
if (minuteCount > 9) { // we are going to test pressure change every 30 min (5*1min + 5*5min)
lastPressureAvg = pressureAvg;
minuteCount = 0;
}
if (minuteCount < 5) {
pressureSamples[minuteCount] = pressure; // Collect 5 minutes of samples every 30 min
Serial.print(" Sample(");
Serial.print(minuteCount);
Serial.print(") = ");
Serial.println(pressure);
}
if (minuteCount == 4) { // the 5th minute
// Avg pressure in first 5 min, value averaged from 0 to 5 min.
pressureAvg = ((pressureSamples[0] + pressureSamples[1]
+ pressureSamples[2] + pressureSamples[3] + pressureSamples[4])
/ 5);
float change = pressureAvg - lastPressureAvg;
dP_dt = (((65.0 / 1023.0) * change) / 0.5); // divide by 0.5 as this is the difference in time from last sample 0.5 hours
Serial.print("dP_dt = ");
Serial.println(dP_dt);
}
minuteCount++;
if (lastPressureAvg < 0) // no previous pressure sample.
return 5; // Unknown, more time needed
else if (dP_dt < (-0.25))
return 4; // Quickly falling LP, Thunderstorm, not stable
else if (dP_dt > 0.25)
return 3; // Quickly rising HP, not stable weather
else if ((dP_dt > (-0.25)) && (dP_dt < (-0.05)))
return 2; // Slowly falling Low Pressure System, stable rainy weather
else if ((dP_dt > 0.05) && (dP_dt < 0.25))
return 1; // Slowly rising HP stable good weather
else if ((dP_dt > (-0.05)) && (dP_dt < 0.05))
return 0; // Stable weather
else
return 5; // Unknown
}
