1.Main Monitor

Description

This is the core of the system acting as gateway between the Lora relay module, the human interface and the network.

It is composed of:

Ethernet module to connect to MQTT server and host a simple webserver
- RTC module to save time and the time is synchronized on regular bases to an NTP server.
- RF95 900Mhz module to communicate via lora radio to the remote lora relay modules
LCD screen with 4 buttons and 1 rotary encoder and 1 buzer as human interface
Aduino mega 2560 as main MCU
Aduino nano as MCU for the RF95 module
5Vdc buck converter
3.3Vdc buck converter

The Arduino mega 2560 is the brain of the system.

The Ethernet module W5500 is connected to the SPI interface.

The RF95 module use SPI as communication port too but the Arduino mega offer only 1 SPI port and because the 2 modules must act as server i can't share the SPI port between them.

I have then connected the RF95 module to an Arduino nano connected to Serial 2 of the Arduino nano.

The RTC module use the ic2 port of the Arduino mega.

The system is powered by a generic 2 amps 12Vdc with 2 buck converter, one 5v for the arduino mega,the aruino nanoand the LCD screen and one 3.3v for the rf95 module. i could have used the 3.3 v from the mega but because it was my first project with lora, i had no idea of the power needed for the lora module in when transmiting. That's why the RF95 got it's dedicaded buck converter. it is little bit over killed but at least the power is stable.

Hardware button debouncing:

To minimize the load of the MCU i try to do an hardware button debouncing based on RC filter and Hex inverter schmit trigger like the 74HC14N as described in the following paper: https://my.eng.utah.edu/~cs5780/debouncing.pdf

I connect everything on perfboard instead of making a PCB because it is going to be a one unit production only :)