SK58 Printer #

Flutter library for SK58 thermal printer via Bluetooth.

Features #

• 🔍 Bluetooth device scanning with permission handling
• 🔌 Connect/disconnect to SK58 thermal printer
• 📝 Print text with styles (bold, underline, sizes) and alignment
• 📊 Print barcodes (Code128, EAN-13, UPC-A, Code39)
• 📱 Print QR codes
• 🖼️ Print images with Floyd-Steinberg dithering
• 🏷️ Generic label templates (Sk58Label, Sk58TwoColumnLabel)
• 🔧 Fluent builder pattern for complex prints
• ✅ Support for Android and Linux

Screenshots #

App Interface #

Main Screen	Barcode Demo	Labels Demo

Print Examples #

Barcode Print	QR Code	Label

Receipt Demo (Builder Pattern) #

Installation #

Add to your pubspec.yaml:

dependencies:
  sk58_printer: ^0.2.0

Then run:

flutter pub get

From Git (development version) #

If you want to use the latest development version from GitHub:

dependencies:
  sk58_printer:
    git:
      url: https://github.com/mosulache/sk58_printer.git
      ref: main

Quick Start #

import 'package:sk58_printer/sk58_printer.dart';

// Create scanner and scan for devices
final scanner = Sk58Scanner();
await scanner.startScan();

// Listen for discovered devices
scanner.deviceStream.listen((device) {
  print('Found: ${device.name}');
});

// Connect to a device
final printer = await Sk58Printer.connect(device);

// Print text
await printer.printText('Hello World!');
await printer.printText('Centered', align: Sk58Align.center);

// Print QR code
await printer.printQrCode('https://example.com');

// Feed paper and disconnect
await printer.feedLines(3);
await printer.disconnect();

Advanced Usage #

Print Barcodes #

// Code 128 (alphanumeric)
await printer.printBarcode('ABC-12345', type: BarcodeType.code128);

// EAN-13 (13 digits)
await printer.printBarcode('5901234123457', type: BarcodeType.ean13);

// UPC-A (12 digits)
await printer.printBarcode('012345678905', type: BarcodeType.upcA);

// Code 39
await printer.printBarcode('CODE39', type: BarcodeType.code39);

Print Images #

final imageBytes = await File('logo.png').readAsBytes();

// Print with dithering (better for photos/grayscale)
await printer.printImage(imageBytes, dithering: true);

// Print with threshold (better for logos/line art)
await printer.printImage(imageBytes, dithering: false, threshold: 128);

// Resize to specific width
await printer.printImage(imageBytes, maxWidth: 200);

// For mobile printers or small labels, use bandMode for reliable printing
await printer.printImage(imageBytes, maxWidth: 280, bandMode: true);

Note: Use bandMode: true for mobile thermal printers or when printing on small labels (e.g., 40x15mm). This sends the image in smaller chunks using ESC * 33 (24-dot double density) which is more reliable for printers with limited buffers.

Use Templates #

// Simple label
await printer.printTemplate(
  Sk58Label(
    title: 'TORX 4x50',
    subtitle: 'Cap T20 - Inox A2',
    qrData: 'SKU-12345',
  ),
);

// Two-column label
await printer.printTemplate(
  Sk58TwoColumnLabel(
    title: 'Product Info',
    rows: [
      ('Type', 'TORX'),
      ('Size', '4x50mm'),
      ('Head', 'T20'),
    ],
  ),
);

Builder Pattern (for complex prints) #

await printer.build()
  .header('DEMO STORE')
  .text('123 Main Street', align: Sk58Align.center)
  .doubleLine()
  .text('RECEIPT', style: Sk58TextStyle.boldStyle, align: Sk58Align.center)
  .line()
  .row('Coffee', '\$3.50')
  .row('Sandwich', '\$8.00')
  .line()
  .row('TOTAL', '\$11.50')
  .feed(1)
  .qrCode('https://receipt.example.com/12345')
  .feed(3)
  .execute();

Text Styles #

// Bold text
await printer.printText('Bold', style: Sk58TextStyle.boldStyle);

// Large text
await printer.printText('Large', style: const Sk58TextStyle(size: Sk58FontSize.large));

// Combined styles
await printer.printText(
  'Bold + Underline',
  style: const Sk58TextStyle(bold: true, underline: true),
);

// Available sizes: normal, wide, tall, large

Printer Specifications (SK58) #

Print Area #

Label Printing - Dead Zone #

⚠️ Important: When printing on label paper, the printer has a non-printable "dead zone" at the top of each label where the print head cannot reach.

Example for 40x15mm label:

• Total label height: 15mm (120 dots)
• Dead zone: ~4mm (32 dots)
• Actual printable height: ~11mm (88 dots)

Image sizing recommendation:

For 40x15mm label → Image should be max 320 x 88 pixels
For 50x25mm label → Image should be max 384 x 168 pixels
For 50x30mm label → Image should be max 384 x 208 pixels

The example app includes a realistic label preview that shows:

• The dead zone (grey area marked "NO PRINT")
• The actual printable area (white)
• How your image fits on the label

Label Commands #

// Print image on label (no extra feed after image)
await printer.printImage(imageBytes, bandMode: true, feedAfter: false);

// Eject to next label (GS FF command)
await printer.printAndPeel();

// Or use form feed
await printer.formFeed();

Platform Setup #

Android #

Add to android/app/src/main/AndroidManifest.xml:

<uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

Linux #

Ensure BlueZ is installed and your user has bluetooth permissions:

sudo apt install bluez
sudo usermod -a -G bluetooth $USER

!! linux support requires more testing / documentation

Example App #

The example/ folder contains a complete demo app with:

• Text printing with styles
• Barcode printing (all types)
• Image printing with dithering options
• Simple Label templates
• Builder pattern demos

Run it:

cd example
flutter run

API Reference #

Sk58Printer #

Sk58Scanner #

Third-Party Licenses #

This project uses the following open-source libraries:

• universal_ble - BSD-3-Clause License (license)
• permission_handler - MIT License (license)
• image - MIT License (license)
• flutter_lints - BSD-3-Clause License (license)

License #

MIT License