Interface PNP-500/RS203 Thermal Printers with ESP32 Microcontroller
Print Receipts • QR Codes • Barcodes • Images • Text
This project demonstrates how to interface thermal printers (PNP-500/RS203) with ESP32 microcontrollers for creating IoT-enabled printing solutions. Perfect for building POS systems, receipt printers, inventory management, and embedded printing applications.
- Multiple Print Formats: Text, Images, QR Codes, Barcodes (CODE128, UPC-A, EAN13)
- Professional Output: High-quality 8 dots/mm resolution printing
- Easy Integration: Simple UART communication interface
- Memory Optimized: Efficient bitmap processing for ESP32 constraints
- Customizable: Adjustable darkness, alignment, and formatting options
- Real-world Ready: Includes GST invoice printing example
| Component | Quantity | Purpose |
|---|---|---|
| ESP32 Development Board | 1 | Main microcontroller |
| PNP-500 or RS203 Thermal Printer | 1 | Printing device |
| 1KΩ Resistors | 2 | Pull-up resistors for signal stability |
| Push Buttons | 2 | Demo triggers (optional) |
| 2S Li-Ion Battery (7.4V) | 1 | Printer power supply |
| Breadboard & Jumper Wires | - | Circuit assembly |
- Print Method: Direct thermal line printing
- Paper Width: 57mm thermal paper
- Print Width: 48mm effective area
- Print Speed: 50-80mm/sec
- Resolution: 8 dots/mm (384 dots/line)
- Interfaces: TTL UART, RS232, USB
- Operating Voltage: 5-9V DC (6V+ recommended for image printing)
- Dimensions: 76.8×77.4×47.6mm (W×D×H)
- Print Head Life: Up to 50km of printing
ESP32 GPIO Pins → Thermal Printer
GPIO16 (RX2) → TTL TX
GPIO17 (TX2) → TTL RX
GPIO5 (GND) → Signal GND (with 1KΩ pulldown)
GPIO21 (VCC) → Signal VCC (with 1KΩ pullup)
GPIO22 → Button 1 (Print Next Image)
GPIO23 → Button 2 (Print Demo Page)
Power Supply:
7.4V Li-Ion → Printer VCC
Common GND → All GND connections
⚠️ Important: Use 6V+ for optimal printing quality. 5V may result in light/poor image prints.
Control the printer via Serial Monitor with these commands:
| Command | Usage | Description |
|---|---|---|
HELP |
HELP |
Show all available commands |
QRCODE |
QRCODE Hello World |
Print QR code with data |
BARCODE |
BARCODE CODE128 123456 |
Print barcode (CODE128/UPCA/EAN13) |
BITMAP |
BITMAP circuitDigestLogo |
Print stored image |
ALIGN |
ALIGN 1 |
Set alignment (0=left, 1=center, 2=right) |
DARKNESS |
DARKNESS 80 500 |
Set print darkness % and delay μs |
TEXTMODE |
TEXTMODE Hello |
Print native text |
UPSIDEDOWN |
UPSIDEDOWN 1 |
Enable/disable upside-down printing |
UNDERLINE |
UNDERLINE 1 |
Set underline mode (0=off, 1=thin, 2=thick) |
INVERSE |
INVERSE 1 |
Enable white text on black background |
FEED |
FEED 3 |
Feed paper n lines |
- CODE128: Variable length alphanumeric
- UPC-A: 11-digit product codes
- EAN13: 12-digit international article numbers
- Error Correction Levels: L(7%), M(15%), Q(25%), H(30%)
- Module Sizes: 3-16 dots per module
- Data Types: Text, URLs, contact info, WiFi credentials
- Supported Format: 1-bit monochrome bitmaps
- Max Resolution: 384 pixels wide (printer limitation)
- Memory Optimized: Chunked processing for large images
- Rotation Support: 180° rotation for upside-down printing
- Connect ESP32 to thermal printer according to circuit diagram
- Connect 7.4V power supply to printer
- Add optional push buttons for demo functionality
-
Clone this repository:
git clone https://github.com/Circuit-Digest/Interfacing-Thermal-Printer-POS-ESC-with-the-ESP32.git
-
Open the project in Arduino IDE
-
Install required libraries:
- ESP32 Board Package
- Arduino Core Libraries (included)
-
Upload the code to your ESP32
- Open Serial Monitor (115200 baud)
- Type
HELPto see all available commands - Try basic commands:
QRCODE https://circuitdigest.comBARCODE CODE128 123456BITMAP circuitDigestLogo
- Prepare Image: Resize to max 384px width, convert to monochrome
- Use Converter: Visit image2cpp
- Settings:
- Set width ≤ 384 pixels
- Select "Arduino Code, single bitmap"
- Invert image if needed (white areas print black)
- Integration: Copy generated code to
data.hfile - Update Code: Add new image to
availableImages[]array
// In data.h
const unsigned char myCustomImage[] PROGMEM = {
0x00, 0x00, 0xFF, ... // Generated bitmap data
};
// In main code
const BitmapImage availableImages[] = {
{ "myCustomImage", myCustomImage, 200, 100 },
// ... other images
};- Button 1 (GPIO22): Cycle through available images
- Button 2 (GPIO23): Print comprehensive demo page with all formats
The printer uses standard ESC/POS commands for control:
- Text Formatting: ESC commands for alignment, underline, inverse
- Graphics: GS v command for bitmap printing with chunking
- Barcodes: GS k command with type-specific parameters
- QR Codes: GS ( k command sequence for modern QR generation
- PROGMEM Storage: Images stored in flash memory to preserve RAM
- Chunked Processing: Large images processed in 24-line chunks
- Dynamic Allocation: Temporary buffers for image rotation and processing
- Memory Monitoring: Built-in heap usage tracking and reporting
- Darkness Control: Adjustable from 50% to 205% in 5% steps
- Heat Timing: Configurable break delays (0-1750μs)
- Paper Feed: Precise line spacing control
- Signal Integrity: Pull-up resistors for noise reduction
| Problem | Cause | Solution |
|---|---|---|
| Light/faded prints | Low voltage supply | Use 6V+ power supply |
| Blurry images | Print head contamination | Clean with isopropyl alcohol |
| No output | Wrong wiring | Check TTL connections and power |
| Memory errors | Large images | Reduce image size or increase chunk processing |
| Paper jam | Wrong paper type | Use 57mm thermal paper |
- 1 blink: Working properly
- 2 blinks: No printer detected
- 3 blinks: No paper detected
- 5 blinks: Print head overheating
- 10 blinks: Font IC missing
How to Interface Thermal Printer with ESP32
Comprehensive guide covering hardware overview, circuit diagrams, code explanation, and practical demonstrations.
- Thermal Printer with Arduino Uno
- Thermal Printer with Raspberry Pi
- Smart Shopping Cart with POS System
- Printer Manual: PNP-500 User Manual
- ESC/POS Commands: Complete command reference included in manual
- Image Converter: Online Bitmap Converter
├── ESP32_Thermal_Printer.ino # Main Arduino sketch
├── data.h # Bitmap image data
├── DOC/
│ └── User Manual PNP-500.pdf # Printer documentation
├── images/ # Sample images for testing
└── README.md # This file
The code includes a complete GST invoice printing example with:
- Company letterhead and logo
- Itemized billing with calculations
- Tax breakdowns and totals
- QR codes for digital verification
- Professional formatting
- Power Management: Software-controlled power pins
- Image Processing: 180° rotation support for upside-down mounting
- Error Handling: Comprehensive validation and error reporting
- Debug Interface: Memory usage monitoring and command logging
We welcome contributions! Please:
- Fork the repository
- Create a feature branch
- Test thoroughly with hardware
- Submit a pull request
This project is licensed under the MIT License - see the LICENSE file for details.
Questions? Issues? Feature Requests?
💬 Open an Issue | 📧 Contact Us
Built with ❤️ by the Circuit Digest Team
ESP32 Thermal-Printer POS ESC-POS Receipt-Printer QR-Code Barcode IoT Arduino Microcontroller PNP-500 RS203 Embedded-Systems Print-Technology