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LoRa Environmental Sensors

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1.0.0

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LoRa Environmental Sensors

Arduino based board for a Atmospheric Sensor BME280 LoRaWan Node. The LoRa Node measures barometric pressure, humidity, and temperature every 5 min. After the measurements, the ATtiny85 goes into sleep mode and is awakened by the watchdog timer. The RFM module sends the values to the TTN backend with Activation by Personalization (ABP) a fixed spreading factor and one of the four random channels. This project is based on the TinyLoRa-BME280 project [1].

BOM

Ref	Value	Description
BT1	3034	Battery Cell Holder
BT1	CR2032	Battery Cell CR2032 (210 – 230 mAh)
U1	BME280	SparkFun BME280
U2	ATtiny85-20SU	Atmel 8-bit AVR Microcontroller
U3	RFM95W-868S2	Low Power Long Range Transceiver Module
-	Wire	Wire for the antenna, 8.6 cm

The ATmega microprocessor needs an arduino bootloader. To burn a bootloader to the blank chip see [2]

Wiring

ATtiny85	RFM95	BME280
PB3		CS (Slave Select)
PB4	NSS (Slave Select)
PB2	SCK	SCK
PB1(DO)	MOSI	SDI
PB0(DI)	MISO	SDO

Installation

The Arduino IDE has to be properly installed.

Add the Libraries to you IDE:

Install the Attiny Baord Manager
- Under Preferences > Additional Boards Manager URLs: https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json
Multiple managers can be separated with a comma.
Install TinyLoRa-BME280 v1.1
- Download the ZIP archive from TinyLoRa-BME280 v1.1
- Install the ZIP archive in the Arduino Library Manager
Open Examples > TinyLoRa-BME280_v1.1-master > ATtiny_LoRa_BME280
- Edit NwkSkey, AppSkey, DevAddr
- Change the Spreading Factor in ATtinyLoRa.cpp
- The Sleep time can be set with the SLEEP_TOTAL var.
Burn the sketch to the Chip using an Arduino UNO [2]
- Burn a bootloader first to set the fuses correctly

Payload Format

The Payload is encoded as byte array.

byte	content
0..1	temperature (*100)
2..3	humidity (*100)
4..8	barometric pressure

To decode the values add this code in the TTM Console as decoder under Paload Formats.

function Decoder(bytes, port) {
  temp = ((bytes[0]) << 8)
              + ((bytes[1]));
  hum = ((bytes[2]) << 8)
              + ((bytes[3]));
  pres = ((bytes[4]) << 24)
              + ((bytes[5]) << 16)
              + ((bytes[6]) << 8)
              + ((bytes[7]));

  return {
    pressure: ( pres / 100 ),
    temperature: ( temp / 100 ),
    humidity: ( hum / 100 )
  };
}