The Secure Circuit
Hey crew,
We are back with a new off-grid project that’s about keeping people connected when the normal network is gone. No, this is not another Meshtastic project.
The new project is Cypher Chat, an ESP32-based off-grid messaging system. It uses ESP-NOW for local mesh networking, USB serial and BLE UART for control, and a project guide that tells the Codex app how to help you build the right device. The point is not to replace ham radio, public safety systems, or Meshtastic. The point is to make a cheap, inspectable emergency comms stack that you can actually build, flash, carry, and understand.
OSI Networking vs. ESP-NOW Networking
Phones make communication feel like an app. Off-grid work reminds you it is a chain: power, radio, firmware, interface, trust, and practice. Cypher Chat is a hands-on way to learn that chain, and Codex makes the first build much less intimidating.
Useful Knowledge
Why Build It?
Off-grid comms matter during outages, storms, wildfires, remote work, field operations, school workshops, and plain old curiosity. Most people do not need a giant system. They need a small first node that teaches the basics:
Can two devices discover each other?
Can a message move without WiFi or cell service?
Can you control the device from a laptop or phone?
Can a non-cloud tool still feel usable in the field?
Cypher Chat starts with inexpensive ESP32 hardware. A bare board can act as a basic mesh node. A Cardputer build adds the part that makes it feel real: screen, keyboard, battery-aware field UI, quick message presets, and local logs.
That is the sweet spot for this issue: one cheap node, one field console, and enough of a mesh to learn from.The repo supports five hardware profiles:
Waveshare touch LCD: the default ST7789 plus touch build.
Waveshare touch AMOLED 1.8: QSPI AMOLED plus FT3168 touch.
M5Stack Cardputer-Adv (Recommended): keyboard, display, microSD, battery-aware field hardware.
ESP32-S3 DevKit serial-only: a no-screen fallback.
SSD1306 Display + three-button build: a tiny 128x64 OLED with up/select/back buttons.
Help From AI:
The Codex Angle
Here I am using the ChatGPT Codex App to develop, build, and flash the Cypher Chat device.
The best part of this project is not that every reader has to memorize board settings or serial-port details. They do not.
The repo includes an AGENTS.md file, which is basically a field manual for the Codex app. It tells Codex what variants exist, what the basic node is, what the Cardputer node is, which libraries are expected, which ports are common, how the build should be verified, and what commands prove the mesh is alive.
That turns the Codex app into a practical build assistant. You can open the project, point Codex at AGENTS.md, plug in a board, and ask for the outcome in plain English:
Use the AGENTS.md instructions and help me build the basic node first. Detect my board, install anything missing, compile it, flash it, and help me verify it from the monitor.
Codex is not guessing from a random internet tutorial. It is following the repo’s own instructions.
That matters because hardware projects fail in boring places: wrong board target, missing library, stale port, wrong upload mode, unclear monitor command, or a device that flashed but was never actually tested. AGENTS.md gives Codex the checklist. Codex gives you the hands-on operator.
THE HARDWARE
What Cypher Chat Does
Cypher Chat turns ESP32 devices into local mesh chat nodes.
The useful bits:
ESP-NOW mesh: nodes talk directly without a router.
Peer discovery: devices announce themselves and find nearby nodes.
Multi-hop relay: messages can move through nearby devices.
Emergency broadcast: a high-priority SOS-style message can be sent across the mesh.
USB and BLE terminal: control the node from a laptop or phone terminal app.
Basic and field-console builds: start with a bare ESP32, then move to Cardputer for typing and status views.
The big design goal is simple: local communication with fewer hidden dependencies, plus enough project guidance that Codex can walk you through the build instead of leaving you to decode every board detail yourself.
TOOLS
Build Your First Two Nodes With Codex
For a first build, focus on two paths:
Build | Best for | Hardware |
|---|---|---|
Basic node | cheapest mesh test | bare ESP32 DevKit-style board |
Cardputer node | practical field console | M5Stack Cardputer-Adv |
Two basic nodes are the cheapest test. One basic node plus one Cardputer is the better demo: a tiny relay/chat node talking to a self-contained keyboard device.
Setting up your mesh network:
1. Start With The Basic Node
Plug in a bare ESP32 board and let Codex do the fussy parts:
confirm the board appears on USB
install anything missing
build the basic-node variant
flash the board
give you the monitor command
help you name the node
verify status, peers, and emergency/cancel behavior
The basic node does not need a screen or keyboard. It just needs to be alive, reachable, and ready to talk.
2. Add The Cardputer Node
The Cardputer is the one I would hand to someone in the field. It has a keyboard, screen, local message logs, quick presets, and a better status experience.
Plug it in and ask Codex to build the Cardputer node using the AGENTS.md instructions. Codex can handle the Cardputer-specific setup, choose the right build path, walk you through upload mode if the device is stubborn, and then help verify that it can see the basic node.
Once it is running, the Cardputer becomes the friendly end of the mesh: type a message, send a preset, open the peer view, and confirm the basic node is nearby.
3. Field Test The Pair
Ask Codex to keep you honest with a field checklist:
name the nodes clearly
confirm both use the same mesh settings
confirm each device sees the other
send one typed Cardputer message
send one preset message
trigger and cancel emergency mode
power-cycle both nodes
walk them apart and write down when messages get unreliable
This is where Codex is genuinely useful. It can be the calm checklist brain while you are juggling cables, ports, boards, and radio behavior.
Your workbench proves it builds. The field proves it communicates.
THE BOTTOM LINE
Cypher Chat is not trying to replace ham radio, Meshtastic, or public safety systems.
It is a small, cheap way to learn the real chain behind communication:
radio
electronics
firmware
interface
security
practice
That is the lesson.
A message is not just an app notification. It is voltage, packets, antennas, firmware, distance, interference, and someone on the other end who knows how to use the tool. Now it’s your turn!
🛠️ Field Stack of the Week:
M5Stack Cardputer-Adv: the recommended field console.
Bare ESP32 node: the cheapest way to test the mesh.
Ask yourself: “What is one piece of technology I rely on that I should understand without the cloud?”
Build one if you want to learn.
Build two if you want to use with a friend!
Stay curious, stay prepared,
Cypher
