Long-Range LoRa Text Messenger for Off-Grid Communication

When the network goes down — in a disaster zone, on a trek, across a large farm — ordinary messaging dies with it. LoRa exists precisely for that gap: chirp spread-spectrum modulation that trades data rate for kilometres of range at milliwatts of power. This project turns that principle into something you can hold: two identical handheld messenger units, each built around an ATmega328P with a Ra-02 433 MHz LoRa module, an OLED display, three message buttons and an AA battery pack. Compose a short text on Unit A, and it appears on Unit B's screen with the received signal strength beside it. The build covers the full peer-to-peer loop — addressing so each unit knows who a message is for, acknowledgements, RSSI-based link quality, and the low-power behavior that lets such units run for days on batteries.

1. The user composes a message on Unit A using the buttons — scrolling presets or entering characters — and presses send.
2. The ATmega328P frames the text with the destination address and a sequence number, and hands it to the Ra-02 LoRa module.
3. The module transmits using chirp spread-spectrum modulation at 433 MHz, which resists interference and reaches far at low power.
4. Unit B's Ra-02 receives the chirps, decodes them, checks the address, and passes the payload to its microcontroller.
5. Unit B displays the message with its measured RSSI and transmits a short acknowledgement back to Unit A.
6. Unit A marks the message delivered on its OLED; if no acknowledgement arrives, it reports the failure honestly instead of pretending.
7. Between activity both units sleep to conserve the AA batteries, waking on button press or incoming preamble.

Tech stack:

• ATmega328P microcontroller (Arduino-compatible)
• Ra-02 LoRa module (SX1278, 433 MHz)
• OLED character/graphic display
• Push-button input interface
• AA battery power with sleep modes
• C/C++ firmware (Arduino IDE)

• [Peer-to-peer LoRa texting] Two identical units exchange addressed text messages directly over the 433 MHz LoRa link, with no gateway or network.
• [OLED chat display] Each unit shows the conversation with unit identity, message direction and status on a crisp OLED.
• [Live RSSI readout] Every received message displays its signal strength (e.g. −71 dBm), turning link quality into a visible, measurable quantity.
• [Button text entry] Three push buttons drive a message composer with preset phrases and character entry, designed for gloved or field use.
• [Addressing and acknowledgements] Unit A / Unit B addressing with delivery acknowledgement, demonstrating reliable transfer over an unreliable medium.
• [Battery operation] AA battery packs with low-power sleep between activity, showing the energy profile that makes LoRa field devices practical.
• [Range-test procedure] A buyer-run procedure for measuring usable range and RSSI fall-off across the student's own test sites.

• Two complete handheld messenger units (PCB, ATmega328P, Ra-02, OLED, buttons, battery pack)
• Peer-to-peer messaging firmware with full source
• Range and RSSI measurement procedure (buyer-run)
• Battery-life estimation worksheet
• Project report PDF (LoRa theory, spread spectrum, link budget, measurements)
• PPT presentation for final review
• Viva Q&A preparation document (chirp modulation, spreading factor, RSSI, addressing)

• Text only, at low data rates — LoRa trades throughput for range; no images, voice or fast chat.
• Real-world range is environment-dependent (buildings, terrain, antenna orientation) and is measured by the student, never pre-claimed.
• Button text entry is deliberately simple and slower than a phone keyboard — a field-device trade-off, stated honestly.
• The 433 MHz band has regional duty-cycle and power rules; the firmware keeps transmissions short and the report notes the regulatory position.
• Acknowledgements confirm delivery between the two units only; there is no store-and-forward for out-of-range units.