Tilli

Tiny LoRa Link
a battery powered wireless sensor or wireless actor using LoRa technology. Target of the project is the development of small size , cost effective battery powered LoRa nodes for IoT.

Project

Tilli is based on TiNo, a wireless sensor in a matchbox. Its footprint fits a RFM95 module using the Semtech SX1276 LoRa transceiver. Together with the ATmega328P AVR processor the hardware can turn into a low cost yet powerful LoRa node.
The following sensors are supported:

• a motion detector
• a brightness detector, using a photodiode -up to four configurable pin change interrupts such as tactile switches, reed contacts, vibration sensors or tilt sensors.
• DS18B20 temperature sensor
• SHT20/SHT21/SHT25 and HTU21D temperature and humidity sensors
• BME280 pressure, humidity and temperature sensor

Firmware

TiLLi Firmware uses the LMIC "Lora Mac in C" Stack available at github

required changes to the mcci-catena LMIC stack

A few changes have to be made to make Tilly work correctly:

1. replace the file lmic_project_config.h in your MCCI_LoRaWAN_LMIC library directory. this removes the support of LoRa Class B, not needed for this project and just occupying flash and RAM space.
2. Change to your region. Default is CFG_eu868.
3. replace the file config.h in the /src/lmic directory. This is needed to allow stable Downlink messages, because Tilly's processor clock is - by design - less accurate than the developpers of LMIC assumed.
4. replace the file radio.c in the /src/lmic directory with radio.cpp. This is needed to measure VCC during the TX slot. Voltage will drop depending on the battery's internal resistance. Experience shows that batteries can maintain their nominal voltage but internal resistance increases with age and discharge considerably. it is critical to maintain voltage above 1.8V during the TX burst, which is the moment of highest current drain.

library dependencies

• LowPower under creative commons attribution-sharealike 3.0 unported license.
• PinChangeInterrupt under open source license, exact type is not specified but looks like GNU
• SoftwareWire under GNU GPL 3.0, used in case devices that communicate through I2C bus are used.
• HTU21D under GNU GPL, modified to work with SoftwareWire. Please pull this library from my repository and copy into your library directory. -BME280 under GNU GPL license, modified to work with SoftwareWire. Please pull this library from my repository and copy into your library directory. -OneWire, license unknown. Used for OneWire devices like the DS18B20 temperature sensor. -DallasTemperatureunder GNU LGPL license. Used for DS18B20 temperature sensor.

Limitations

• ABP (activation by personalization) only
• LoRa Keys need to be copied into source code.
• individual node configuration possible, but by LoRa downlink only.