Batterie + Solar + 3D Gehäuse + Arduino Pro Mini + RFM95W + DHT22

Finally a real application

Hello friends,

I apologize for the rare posts, I’ve been employed in a makerspace for a few weeks now and I’m not coming to write something. Great fun, but documenting here in the blog…

So, as mentioned in the headline: The first node is running 🙂 Sending every 10 Minutes.

Livedata

Temperature:

Humidity:

Battery:

 

Construction

The board from the post  “My first own TTN node with self designed PCB” certainly known to you, otherwise read the article;)

The structure is thus very simple. The board has everything we need, the DHT22 temperature sensor is simply soldered to the Arduino and ready.

The solar cell is very small, the battery also only in AA (14500) format. No problem with sunshine. We will see how the combination works in winter! I’m curious! However, the battery should last long enough so that winter should not be a problem.

Data processing

The Things Network -> Payload -> NodeRed -> Thingspeak / own Database / …

Technical specifications

• Arduino Pro Mini 3.3V (LowPower mods)
• RFM95W
• 0.15W 5V solar cell
• 900mAh 3.7V LiPo
• Running time about 2 years without sun?
• 5 days sun to fully charge

Runtime Bill

As we learned in the LowPower article here we can expect self-discharge, now and then, deep sleep to consume about 0.04mA.

At 900mAh battery and 0.04mA consumption we come to 900 days. Therefore, winter should not be a problem! Top!

Here’s how the real consumption showed up after 5 months.

Code

// Default LoRa libs
#include <lmic.h>
#include <hal/hal.h>
#include <SPI.h>

// For this Sketch
#include <Wire.h>
#include "DHT.h"
#include <LowPower.h>

// DHT Sensor
#define DHTPIN 8
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

// Enable debug prints to serial monitor
#define MY_DEBUG

// For Mario PCB
int BATTERY_SENSE_PIN = A0;
int BATTERY_FULL = 4.2;

// This EUI must be in little-endian format, so least-significant-byte
// first. When copying an EUI from ttnctl output, this means to reverse
// the bytes. For TTN issued EUIs the last bytes should be 0xD5, 0xB3,
// 0x70.
static const u1_t PROGMEM APPEUI[8] = { ToDo };
void os_getArtEui (u1_t* buf) {
  memcpy_P(buf, APPEUI, 8);
}

// This should also be in little endian format, see above.
static const u1_t PROGMEM DEVEUI[8] = { ToDo };
void os_getDevEui (u1_t* buf) {
  memcpy_P(buf, DEVEUI, 8);
}

// This key should be in big endian format (or, since it is not really a
// number but a block of memory, endianness does not really apply). In
// practice, a key taken from ttnctl can be copied as-is.
// The key shown here is the semtech default key.
static const u1_t PROGMEM APPKEY[16] = { ToDo };
void os_getDevKey (u1_t* buf) {
  memcpy_P(buf, APPKEY, 16);
}

static uint8_t mydata[] = "Hello, world!"; // Default
static osjob_t sendjob;

// 10min -> 12:10 -> 130s zuviel -> pro minute 13s zuviel
#define SECPROMIN 13

// Schedule TX every this many seconds (might become longer due to duty
// cycle limitations).
const unsigned TX_INTERVAL_MINUTES = 10;
const unsigned TX_INTERVAL = (60 - SECPROMIN) * TX_INTERVAL_MINUTES;

// Pin mapping for Mario PCB
const lmic_pinmap lmic_pins = {
  .nss = 10,
  .rxtx = LMIC_UNUSED_PIN,
  .rst = 9,
  .dio = {4, 5, 7},
};

void onEvent (ev_t ev) {
  Serial.print(os_getTime());
  Serial.print(": ");
  switch (ev) {
    case EV_SCAN_TIMEOUT:
      Serial.println(F("EV_SCAN_TIMEOUT"));
      break;
    case EV_BEACON_FOUND:
      Serial.println(F("EV_BEACON_FOUND"));
      break;
    case EV_BEACON_MISSED:
      Serial.println(F("EV_BEACON_MISSED"));
      break;
    case EV_BEACON_TRACKED:
      Serial.println(F("EV_BEACON_TRACKED"));
      break;
    case EV_JOINING:
      Serial.println(F("EV_JOINING"));
      break;
    case EV_JOINED:
      Serial.println(F("EV_JOINED"));

      // Disable link check validation (automatically enabled
      // during join, but not supported by TTN at this time).
      LMIC_setLinkCheckMode(0);
      break;
    case EV_RFU1:
      Serial.println(F("EV_RFU1"));
      break;
    case EV_JOIN_FAILED:
      Serial.println(F("EV_JOIN_FAILED"));
      break;
    case EV_REJOIN_FAILED:
      Serial.println(F("EV_REJOIN_FAILED"));
      break;
      break;
    case EV_TXCOMPLETE:
      Serial.println(F("EV_TXCOMPLETE (includes waiting for RX windows)"));
      if (LMIC.txrxFlags & TXRX_ACK)
        Serial.println(F("Received ack"));
      if (LMIC.dataLen) {
        Serial.println(F("Received "));
        Serial.println(LMIC.dataLen);
        Serial.println(F(" bytes of payload"));
      }
      // Schedule next transmission
      for (int i = 0; i < int(TX_INTERVAL / 8); i++) {
        // Use library from https://github.com/rocketscream/Low-Power
        LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
      }
      do_send(&sendjob);
      break;
    case EV_LOST_TSYNC:
      Serial.println(F("EV_LOST_TSYNC"));
      break;
    case EV_RESET:
      Serial.println(F("EV_RESET"));
      break;
    case EV_RXCOMPLETE:
      // data received in ping slot
      Serial.println(F("EV_RXCOMPLETE"));
      break;
    case EV_LINK_DEAD:
      Serial.println(F("EV_LINK_DEAD"));
      break;
    case EV_LINK_ALIVE:
      Serial.println(F("EV_LINK_ALIVE"));
      break;
    default:
      Serial.println(F("Unknown event"));
      break;
  }
}

void do_send(osjob_t* j) {
  // Read sensor values and multiply by 100 to effectively keep 2 decimals
  // Signed 16 bits integer, -32767 up to +32767
  int16_t t = dht.readTemperature() * 100;
  // Unsigned 16 bits integer, 0 up to 65535
  uint16_t h = dht.readHumidity() * 100;
  // Unsigned 16 bits integer, 0 up to 65535
  uint16_t b = readBat() * 100;
  byte buffer[6];
  buffer[0] = t >> 8;
  buffer[1] = t;
  buffer[2] = h >> 8;
  buffer[3] = h;
  buffer[4] = b >> 8;
  buffer[5] = b;
  LMIC_setTxData2(1, buffer, sizeof(buffer), 0);

#ifdef MY_DEBUG
  Serial.println("");
  Serial.print("temperature: ");
  Serial.print(t);
  Serial.print(", humidity: ");
  Serial.print(h);
  Serial.print(", battery: ");
  Serial.print(b);
  Serial.println("");
#endif

  // Check if there is not a current TX/RX job running
  if (LMIC.opmode & OP_TXRXPEND) {
    Serial.println(F("OP_TXRXPEND, not sending"));
  } else {
    // Prepare upstream data transmission at the next possible time.
    LMIC_setTxData2(1, buffer, sizeof(buffer), 0);
    // LMIC_setTxData2(1, mydata, sizeof(mydata) - 1, 0);
    Serial.println(F("Packet queued"));
  }
  // Next TX is scheduled after TX_COMPLETE event.
}

void setup() {
  Serial.begin(115200);
  Serial.println(F("Starting"));

  // Fuer A0 Battery:
  analogReference(INTERNAL);

  dht.begin();
  delay(2000);

#ifdef VCC_ENABLE
  // For Pinoccio Scout boards
  pinMode(VCC_ENABLE, OUTPUT);
  digitalWrite(VCC_ENABLE, HIGH);
  delay(1000);
#endif

  // LMIC init
  os_init();
  // Reset the MAC state. Session and pending data transfers will be discarded.
  LMIC_reset();

  // Start job (sending automatically starts OTAA too)
  do_send(&sendjob);
}

float readBat() {
  int sensorValue = analogRead(BATTERY_SENSE_PIN);
#ifdef MY_DEBUG
  Serial.println(sensorValue);
#endif
  // 1M, 470K 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+470e3)/470e3)*1.1 = Vmax = 3.44 Volts
  // 3.44/1023 = Volts per bit = 0.003363075

  // 2M, 470K 1.1V ref => 5,78V Max!
  // 5,78/1023 = 0.00565
  float batteryV  = sensorValue * 0.00565;

#ifdef MY_DEBUG
  Serial.print("Battery Voltage: ");
  Serial.print(batteryV);
  Serial.println(" V");
#endif
  return batteryV;
}

void loop() {
  os_runloop_once();
}

Affiliate links:

If you order through any of the following AliExpress links, I get about 8% commission 😉

Soshine 4pc 3.7V ICR 14500 900mAh Li-ion
Mini 0.15W 5V Solar Panel
DHT22 single-bus digital temperature and humidity sensor