mesh-433

A self-healing mesh network for $2 433 MHz radio modules (FS1000A / XY-MK-5V) on Arduino Uno/Nano.

Built and running on real hardware: PIR sensor nodes send alerts to a master with an LCD and buzzer. Nodes that can't reach the master relay through each other, and find a new route when a relay dies.

[node 3] ))) [node 2] ))) [node 1] ))) [MASTER]   "Motion at 3"
    \                                  /
     ))) [node 5] ))) [node 4] ))) ----          used if node 2 dies

How it works

• One sketch and one packet format for every board, so any node can relay for any other
• Relay discovery by hop count, with per-hop acks and automatic failover
• Random backoff and short control frames to dodge collisions (ASK, amplitude-shift keying: these on/off radios can't hear each other transmit)
• Duplicate and loop protection: hop limit, sequence numbers, boot counter in EEPROM
• Commands go back down the mesh (arm/disarm from the master)
• No delay(), so nodes keep listening

Build

Libraries: RadioHead, LiquidCrystal I2C. Set NODE_ID in mesh433.ino (0 = master), then:

arduino-cli compile -b arduino:avr:uno firmware/mesh433
arduino-cli upload -p /dev/ttyUSB0 -b arduino:avr:uno firmware/mesh433

Part	Pin
RX data / TX data	D11 / D12
PIR	D2
Button (to GND)	A1
TX LED / alert LED / buzzer	D5 / D6 / D7
16x2 LCD (I2C 0x27)	A4, A5

D10 is taken: RadioHead's RH_ASK driver uses it as its push-to-talk pin by default.

A 17 cm wire antenna helps a lot.

Regression tests

make -C test test

The same mesh.h also compiles on a PC, so routing changes get checked against a model of the ASK link (collisions, loss) before they go on the boards: chains, failover, a lossy 3x3 grid, an 8-node alarm storm, reboots, millis() rollover and downlink fan-out.

Todo

• Packet authentication (MAC + counter)
• Heartbeats and jamming alerts
• Sleeping battery nodes
• RFM69 / LoRa radios

License

Copyright (c) 2026 codemonkeying. All rights reserved.