Lightweight Arduino logging library for consistent Serial output. Adds optional prefix, millis timestamp, log levels with filtering, and type-safe variadic logging (C# params style) so you can write sw.info("Backoff", backoff, "ms") without repetitive Serial.print chains.

• Consistent log line format
• Optional prefix (example: NET)
• Optional millis() timestamp
• Log levels: Debug, Info, Warn, Error
• Minimum log level filtering
• Variadic logging with any number of parts
• Separator helper: drawLine() prints a horizontal line with the current header; configurable via options
• Introspection helper: printOptions() emits the current configuration in one line
• No dynamic memory allocation, prints directly to Stream

Create this structure in your Arduino sketchbook libraries folder:

O3SerialWriter/
  library.properties
  src/
    O3SerialWriter.h

Restart Arduino IDE.

Copy the O3SerialWriter folder into your sketchbook libraries folder, or add as a git submodule there.

#include <O3SerialWriter.h>

O3SerialWriter sw;

void setup() {
  O3SerialWriterOptions options;
  options.prefix = "NET";
  options.showMillis = true;
  options.showLevel = true;
  options.minLevel = O3LogLevel::Debug;
  options.partSeparator = " ";

  sw.begin(Serial, 115200, options);

  sw.info("Boot");
}

void loop() {
  int backoff = 250;
  int attempt = 3;
  int statusCode = 503;

  sw.info("Backoff", backoff, "ms");
  sw.warn("HTTP", statusCode, "retry in", backoff, "ms", "attempt", attempt);

  delay(1000);
}

Example output:

[NET] 1234 INFO: Boot
[NET] 2234 INFO: Backoff 250 ms
[NET] 3234 WARN: HTTP 503 retry in 250 ms attempt 3

O3SerialWriterOptions:

• prefix: text printed at the beginning of every line
• showMillis: prints millis() when true
• showLevel: prints DEBUG/INFO/WARN/ERROR when true
• minLevel: filters out logs below this level
• partSeparator: string printed between variadic parts
• lineLength: default line length used by drawLine() (default 40)
• lineCharacter: default character used by drawLine() (default -)

Example:

O3SerialWriterOptions options;
options.prefix = "BLE";
options.minLevel = O3LogLevel::Warn;
options.partSeparator = " | ";

sw.begin(Serial, 115200, options);

sw.debug("This will not print");
sw.warn("Disconnected", "reason", 19);

Use printOptions() to emit the current configuration (prefix, millis, level, minLevel, separators, line settings):

sw.printOptions();

Example output:

[BLE] 1234 INFO: options enabled=true prefix="BLE" showMillis=true showLevel=true minLevel=WARN partSeparator=" | " lineLength=40 lineCharacter='-'

If you want to manually build a line, the header is printed only once per line:

sw.printWithLevel(O3LogLevel::Info, "Backoff ");
sw.printWithLevel(O3LogLevel::Info, 250);
sw.printlnWithLevel(O3LogLevel::Info, " ms");

Call drawLine() to print a horizontal line with the usual header (prefix/millis/level). You can configure defaults via O3SerialWriterOptions::lineLength and lineCharacter, and override per-call when needed:

O3SerialWriterOptions options;
options.lineLength = 32;
options.lineCharacter = '=';

sw.begin(Serial, 115200, options);

sw.drawLine();        // uses defaults from options (32 '=' characters)
sw.drawLine(48, '#'); // override per call

MIT.