MailboxSensor

LoRa 868 MHz mailbox detection system with Home Assistant integration. Detects mail delivery via a reed switch and reports wirelessly via LoRa to an ESP32-C3 receiver running MQTT.

The receiver also handles plant sensor packets from a separate PlantSensor node.

System Overview

[ATtiny85 + LoRa]  ---868MHz--->  [ESP32-C3 + LoRa]  ---MQTT--->  [Home Assistant]
  Mailbox transmitter              Combined receiver
  (reed switch, battery)           (WiFi, MQTT, NTP)

Features

• Reed switch triggers mail detection event
• LoRa packet types: S (startup), M (mail), H (health/hourly heartbeat)
• ACK protocol with 3 retries for reliability
• Sequence number deduplication
• VCC battery monitoring via ATtiny internal reference
• EEPROM persistence for sequence counter and event count
• ISO-8601 last delivery timestamp via NTP
• Full MQTT auto-discovery for Home Assistant

Receiver — Sketches/plant_receiver/

ESP32-C3 with LoRa SX127x. Handles mailbox and plant packets.

Hardware (receiver)

Component	GPIO
LoRa SCK	4
LoRa MISO	5
LoRa MOSI	6
LoRa SS	7
LoRa RST	2
LoRa DIO0	3
LED Blue	10
LED Green	9

Setup (receiver)

1. Copy Sketches/plant_receiver/secrets.h.example to secrets.h
2. Fill in WiFi and MQTT credentials
3. Flash to ESP32-C3

Transmitter — Sketches/mailbox_transmitter/

ATtiny85 with soft-SPI LoRa SX127x. Powered by a small LiPo. No WiFi — LoRa only.

Hardware (transmitter)

Component	Pin
Reed switch	PB5 (INT0)
LoRa SCK (soft)	PB3
LoRa MOSI (soft)	PB0
LoRa MISO (soft)	PB1
LoRa SS	PB4
LoRa RST	PB2

Home Assistant Entities

Entity	Type	Description
Mailbox Mail	binary_sensor	ON when mail detected
Mailbox Battery	sensor	Battery %
Mailbox Battery mV	sensor	Raw battery voltage
Mailbox Event Count	sensor	Total mail events
Mailbox Last Delivery	sensor	ISO timestamp
Mailbox RSSI / SNR	sensor	Link quality
Mailbox Reset Mail	button	Clear mail state

Libraries required

Receiver:

• LoRa by Sandeep Mistry
• PubSubClient by Nick O'Leary

Transmitter:

• Custom soft-SPI LoRa driver (included)