CmdMessenger

A command-based messaging library for Arduino that enables structured communication between microcontrollers and PC applications over serial, Bluetooth, or TCP/IP.

Documentation · Examples · C# Client · PyCmdMessenger (Python)

Install

Arduino Library Manager (recommended):

Search for "CmdMessenger" in Sketch → Include Library → Manage Libraries.

PlatformIO:

lib_deps = CmdMessenger

Quickstart

#include <CmdMessenger.h>

enum { kSetLed, kStatus };

CmdMessenger cmdMessenger = CmdMessenger(Serial);

void onSetLed(void) {
  bool ledState = cmdMessenger.readBoolArg();
  digitalWrite(13, ledState ? HIGH : LOW);
  cmdMessenger.sendCmd(kStatus, ledState);
}

void setup() {
  Serial.begin(115200);
  cmdMessenger.attach(kSetLed, onSetLed);
  pinMode(13, OUTPUT);
}

void loop() {
  cmdMessenger.feedinSerialData();
}

Send 0,1; from the serial monitor to turn on the LED; it responds with 1,1;.

Features

• Send and receive commands with zero or more typed arguments
• All primary data types — bool, int16, int32, float, double, char, string, binary
• Plain text or binary encoding — human-readable or efficient, your choice
• Callback-driven — attach handler functions to command IDs
• Separator-free arguments — sendArg() family for custom packet formats
• Configurable delimiters — field separator (,) and command separator (;) are changeable
• Multiple transports — Serial USB, Bluetooth, TCP/IP
• PC companion libraries — full C# (.NET) and Visual Basic implementations included

Compatibility

• Arduino AVR (Uno, Mega, Nano, Pro Micro, etc.)
• Arduino ARM (Due, Zero)
• ESP8266 and ESP32
• Teensy 3.x / 4.x
• Any board with a Stream-compatible interface

Requires Arduino IDE 1.5+ or PlatformIO.

Examples

The examples/ folder contains sketches from basic to advanced, each with a matching C# PC counterpart:

Example	Demonstrates
Receive	Receive commands with parameters
SendAndReceive	Bidirectional communication
SendAndReceiveArguments	Multiple typed arguments
SendAndReceiveBinaryArguments	Efficient binary encoding
SendWithoutSeparator	sendArg() family for custom formats
DataLogging	Charting with ZedGraph
ArduinoController	GUI control with queued commands
TemperatureControl	PID control with live charting
SimpleWatchdog	Auto-reconnect over serial
ConsoleShell	Interactive serial shell (no PC app)

Running the paired examples

1. Upload the .ino sketch to your board.
2. Open extras/CSharp/CmdMessenger.sln in Visual Studio.
3. Set the matching project as startup, then run.

Troubleshooting

• Cannot connect — verify COM port and baud rate match. Use the ConsoleShell example with the Arduino Serial Monitor to test.
• Callbacks not firing — enable logging; see the SendAndReceiveArguments example.
• Sparkfun Pro Micro — set DtrEnable = true on the PC side.
• Unit tests — run the CommandMessengerTests project in the C# solution for systematic checks.

Credits

Version	Author
Messenger (original)	Thomas Ouellet Fredericks
CmdMessenger v1	Neil Dudman
CmdMessenger v2	Dreamcat4
CmdMessenger v3–v4	Thijs Elenbaas & Valeriy Kucherenko

License

MIT — Copyright © 2013–2026 Thijs Elenbaas.

Changelog

v4.1.0

• [Arduino] sendArg(), sendSciArg(), sendBinArg() — send arguments without field separator
• [Arduino] unescape() applied to string reads (fixes escaped delimiter handling)
• [Arduino] Bounds-checked readBinArg<T>() with ArgOk validation
• [Arduino] Configurable CMDMESSENGER_MAXCALLBACKS with compile-time zero-callback support
• [Arduino] ESP8266/ESP32 type fixes
• [Arduino] LastArgLength tracking in argument parser
• Fix: startCommand initialization
• Fix: comms->print used consistently (no direct Serial.print)
• Fix: LICENSE.md reformatted for GitHub detection

v4.0.0

• [Arduino] Additional autoConnect sample
• [.Net/.Mono] Full threading redesign
• [.Net/.Mono] AutoConnect & watchdog functionality
• [.Net/.Mono] Tested Linux compatibility
• [.Net/.Mono] Visual Basic samples
• [.Net/.Mono] Native Bluetooth support (Windows only)

v3.6

• [Arduino] Bugfix: ~1 in 1000 commands failed with multiple binary parameters
• [Arduino] Bugfix: binary send of non-number compile error
• [Arduino] Feature: send command without argument
• [Arduino] Feature: scientific notation for full float range
• [.Net/.Mono] Unit tests, performance improvements

v3.5

• [Arduino] Console shell sample, minor performance improvement

v3.4

• [Arduino] Bug-fix in receiving binary values
• [.Net/.Mono] 100× faster communication, single-core support

v3.3

• [Arduino] Speed improvements for Teensy

v3.2

• [All] Clean transport layer interface (Bluetooth, ZigBee, Web)
• [.Net/.Mono] Adaptive throttling, smart queuing

v3.0

• Multi-argument commands, type arguments, binary data, escaping, acknowledgements

v2

• Arduino IDE 022, configurable separators, Base-64 encoding, Serial Monitor debugging