Particle Photon + DHT22: optimizing battery life

Hardware
1

Hi all,

I have a perfectly working setup of Particle Photon and DHT22.

I would like to make it wireless but it works for a very short amount of time on a huge 9200 mAh battery pack.
This is 100% related to using sleep and deep sleep.

Do you have any suggestions about how to implement this correctly?

Is it possible to “permanently” publish a variable in particle cloud so I can let my application retrieve data from cloud and keep my Photon + DHT22 in deep sleep until next update?

This is my current code:

// Acquire sensor data from Particle Photon
//
// To read variables from Particle Api use:
// https://api.particle.io/v1/devices/YOUR_DEVICE_ID/humidity/?access_token=YOUR_ACCESS_TOKEN
//
// 

#include "PietteTech_DHT/PietteTech_DHT.h"
#include "math.h"

#define DHTTYPE  DHT22       // Sensor type DHT11/21/22/AM2301/AM2302
#define DHTPIN   D2           // Digital pin for communications

// declaration
void dht_wrapper(); // must be declared before the lib initialization

// library instialization
PietteTech_DHT DHT(DHTPIN, DHTTYPE, dht_wrapper);

int n;      // sensor acquisition counter
double temp;  // temperature  
double umid;  // humidity
double t;   // needed in rounding

void dht_wrapper() {
    DHT.isrCallback();
}



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

    Serial.println("Device starting...");

    Serial.println("DHT Example program using DHT.acquireAndWait");
    Serial.print("LIB version: ");
    Serial.println(DHTLIB_VERSION);
    Serial.println("---------------");
    
    pinMode(D7, OUTPUT);

    Particle.variable("humidity", umid); //write the value on the cloud variable called "Humidity"
    Particle.variable("temperature", temp); //write the value on the cloud variable called "Temperature"

}


void loop()
{
    Serial.print("\n");
    Serial.print(n);
    Serial.print(": Retrieving information from sensor: ");
    Serial.print("Read sensor: ");
    delay(100);

    int result = DHT.acquireAndWait();

    
    // Error handling
    switch (result) {
        case DHTLIB_OK:
            Serial.println("OK");
            break;
        case DHTLIB_ERROR_CHECKSUM:
            Serial.println("Error\n\r\tChecksum error");
            break;
        case DHTLIB_ERROR_ISR_TIMEOUT:
            Serial.println("Error\n\r\tISR time out error");
            break;
        case DHTLIB_ERROR_RESPONSE_TIMEOUT:
            Serial.println("Error\n\r\tResponse time out error");
            break;
        case DHTLIB_ERROR_DATA_TIMEOUT:
            Serial.println("Error\n\r\tData time out error");
            break;
        case DHTLIB_ERROR_ACQUIRING:
            Serial.println("Error\n\r\tAcquiring");
            break;
        case DHTLIB_ERROR_DELTA:
            Serial.println("Error\n\r\tDelta time to small");
            break;
        case DHTLIB_ERROR_NOTSTARTED:
            Serial.println("Error\n\r\tNot started");
            break;
        default:
            Serial.println("Unknown error");
            break;
    }


    // humidity rounding
    umid=DHT.getHumidity();
    t=umid-floor(umid);  // get only decimal part
    t=t*100; // multiply by 100 decimal part, get xx.xxxxxxxxx
    t=floor(t); // get only last two characters of decimal part, get yy
    umid=floor(umid)+(t/100);


    // temperature rounding
    temp=DHT.getCelsius();
    t=temp-floor(temp); // get only decimal part
    t=t*100; // multiply by 100 decimal part, get xx.xxxxxxxxx
    t=floor(t); // get only last two characters of decimal part, get yy
    temp=floor(temp)+(t/100);


    // print sensor data to serial
    Serial.print("Humidity (%): ");
    Serial.println(DHT.getHumidity(), 2);

    Serial.print("Temperature (oC): ");
    Serial.println(DHT.getCelsius(), 2);

    Serial.print("Temperature (oF): ");
    Serial.println(DHT.getFahrenheit(), 2);

    Serial.print("Temperature (K): ");
    Serial.println(DHT.getKelvin(), 2);

    Serial.print("Dew Point (oC): ");
    Serial.println(DHT.getDewPoint());

    Serial.print("Dew Point Slow (oC): ");
    Serial.println(DHT.getDewPointSlow());

    
    // Blink onboard led
    digitalWrite(D7, HIGH);
    delay(1000);
    digitalWrite(D7, LOW);


    // Increase acquisition counter
    n++;
    

    // Wait for 10 minutes
    delay(600000);
}
2

delay does not save power, just halt program execution.

You need to use SLEEP_MODE_DEEP for the long wait, which will return your program to the start after the duration and all variables that are not persisted will be reset.
https://docs.particle.io/reference/firmware/photon/#sleep-sleep-

3

No, the Particle cloud does not store data, but there are a lot of free or inexpensive services out there that do (Ubidots, librato, ThingSpeak, etc).

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4

Use Particle.publish() to publish the data. Particle.variable() only serves a variable when requested (while awake).

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5

Are you sure about this?

It seems like this works only for events (reading docs now).

6

Particle.publish will publish a value to particle cloud, where it then needs to be picked up by something (subscribe) or trigger a webhook.

Publish is an event, but it can carry data with it, so the event could be sensorReading, “25.67” for example.

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