253 lines
9.1 KiB
Markdown
253 lines
9.1 KiB
Markdown
# Thermal Printer Wiring Guide for Raspberry Pi 4
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## ⚠️ CRITICAL: Printer RX ↔ Pi TX, Printer TX ↔ Pi RX (CROSSED!)
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## Correct Connection Diagram
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```
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Thermal Printer (58mm) Raspberry Pi 4
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┌──────────────────┐ ┌─────────────────────┐
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│ │ │ │
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│ VCC/5V ├──X───────────────────│ │ ❌ DO NOT connect to Pi
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│ (Connect to │ │ │ │ (Use external 9V PSU)
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│ external PSU) │ │ │ │
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│ │ │ │ │
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│ GND ────────────┼──┼───────────────────┼─► Pin 6 (GND) │ Ground to Pi
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│ (Black/Blue) │ │ │ │
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│ │ │ │ │
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│ RX ─────────────┼──┼───────────────────┼─► Pin 8 (GPIO14/TX) │ Printer receives from Pi
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│ (Yellow/Green) │ │ │ │
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│ │ │ │ │
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│ TX ─────────────┼──┼───────────────────┼─► Pin 10 (GPIO15/RX)│ Printer sends to Pi
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│ (White/Green) │ │ │ │ (optional)
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│ │ │ │ │
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└──────────────────┘ │ └─────────────────────┘
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│
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└─► External 9V PSU GND (also connect to Pi GND)
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External 9V Power Supply
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┌──────────────────┐
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│ 9V PSU │
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│ (+) ────────────┼─► Printer VCC/5V
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│ (-) ────────────┼─► Printer GND + Pi Pin 6 (GND) - COMMON GROUND!
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└──────────────────┘
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```
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## Step-by-Step Wiring Instructions
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### 1. Power Connections (External PSU)
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```
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External 9V PSU (+) ──► Printer VCC/5V pin
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External 9V PSU (-) ──► Printer GND pin
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└─► Raspberry Pi Pin 6 (GND) - MUST share common ground!
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```
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### 2. Data Connections (Pi ↔ Printer)
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```
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Raspberry Pi Pin 8 (GPIO14 TX) ──► Printer RX pin
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Raspberry Pi Pin 10 (GPIO15 RX) ──► Printer TX pin (optional, can skip)
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```
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## Raspberry Pi GPIO Pinout (Top View)
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```
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┌─────────────────────────┐
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│ USB USB Ethernet │
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│ ┌┐ ┌┐ ┌───┐ │
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└──┘└───┘└──────────┘ └─┘
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GPIO Header (40 pins)
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┌────────────────────────┐
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│ 3V3 [●1] [2●] 5V │ ❌ Don't use for printer power
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│ [●3] [4●] 5V │
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│ [●5] [6●] GND │ ◄── Connect Printer GND + PSU GND HERE
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│ [●7] [8●] TX │ ◄── Connect Printer RX HERE (GPIO14)
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│ GND [●9] [10●] RX │ ◄── Connect Printer TX HERE (GPIO15) - optional
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│ [11] [12] │
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│ [13] [14] GND │
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│ [15] [16] │
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│ 3V3 [17] [18] │
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│ [19] [20] GND │
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└────────────────────────┘
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```
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## Wire Connection Table
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| What to Connect | Where It Goes | Pi Pin # | Notes |
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|----------------|---------------|----------|-------|
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| **Printer GND** | Pi Pin 6 (GND) | **6** | Black/Blue wire |
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| **PSU GND (-)** | Pi Pin 6 (GND) | **6** | Share with printer GND |
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| **Printer RX** | Pi Pin 8 (TX/GPIO14) | **8** | Yellow/Green wire - DATA OUT |
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| **Printer TX** | Pi Pin 10 (RX/GPIO15) | **10** | White/Green wire - optional |
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| **Printer VCC** | External PSU (+) | **N/A** | Red wire - NOT to Pi! |
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| **PSU (+)** | Printer VCC | **N/A** | 9V power supply positive |
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## Visual Reminder: TX ↔ RX Crossover
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```
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Raspberry Pi Wire Thermal Printer
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┌──────────┐ ┌──────────────┐
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│ │ │ │
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│ TX ────┼───────────────────────┼──► RX │ Pi talks → Printer listens
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│ (Pin 8) │ │ │
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│ │ │ │
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│ RX ◄───┼───────────────────────┼──── TX │ Printer talks → Pi listens
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│ (Pin 10) │ │ │ (optional)
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│ │ │ │
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│ GND ───┼───────────────────────┼──── GND │ Common ground
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│ (Pin 6) │ └────────────────┼──── PSU (-) │ All grounds together!
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│ │ │ │
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└──────────┘ └──────────────┘
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│
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├──── VCC ◄─── PSU (+)
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│
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```
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## Testing Steps
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### 1. Enable Serial Port on Raspberry Pi
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```bash
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# Open configuration
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sudo raspi-config
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# Navigate to:
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# 3 Interface Options → I6 Serial Port
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# "Login shell over serial?" → No
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# "Serial port hardware enabled?" → Yes
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# Finish and reboot
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sudo reboot
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```
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### 2. Verify Serial Device
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```bash
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# Check serial device
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ls -l /dev/serial0
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ls -l /dev/ttyAMA0
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# Both should exist and point to UART
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```
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### 3. Install Test Tools
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```bash
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sudo apt update
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sudo apt install python3 python3-pip python3-venv
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# Create test environment
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python3 -m venv test_env
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source test_env/bin/activate
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pip install python-escpos pyserial
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```
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### 4. Test Print Script
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Create `test_printer.py`:
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```python
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#!/usr/bin/env python3
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from escpos.printer import Serial
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# Try different device paths if needed
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# Common: /dev/serial0, /dev/ttyAMA0, /dev/ttyS0
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try:
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printer = Serial(
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devfile='/dev/serial0', # or /dev/ttyAMA0
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baudrate=19200,
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timeout=1
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)
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print("Printer initialized successfully!")
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printer.text("Hello from Raspberry Pi!\n")
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printer.text("AutoKanban Test Print\n")
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printer.text("=" * 32 + "\n")
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printer.cut()
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print("Print sent successfully!")
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except Exception as e:
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print(f"Error: {e}")
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print("\nTroubleshooting:")
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print("1. Check wiring connections")
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print("2. Verify serial port is enabled: sudo raspi-config")
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print("3. Check user is in dialout group: groups")
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print("4. Try different baudrates: 9600, 19200, 115200")
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print("5. List available devices: ls -l /dev/tty*")
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```
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### 5. Run Test
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```bash
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# Make sure user is in dialout group
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sudo usermod -a -G dialout $USER
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# Log out and back in, or:
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newgrp dialout
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# Run test
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python3 test_printer.py
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```
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## ⚠️ Power Considerations
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**Important**: Thermal printers can draw 1-2A during printing. The Pi's 5V pins can provide limited current.
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**If the printer doesn't work or the Pi reboots during printing:**
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1. Use an external 5V power supply (2A or higher):
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```
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External 5V PSU
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┌────────────┐
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│ 5V GND │
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│ │ │ │
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└──┼─────┼───┘
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│ │
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│ └──────────┬─► Pi Pin 6 (GND)
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│ └─► Printer Black wire
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│
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└────────────────────► Printer Red wire
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```
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2. Common ground is critical - connect:
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- External PSU GND → Printer Black
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- External PSU GND → Pi GND (Pin 6)
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- This ensures both devices share the same ground reference
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## Troubleshooting
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### No output from printer
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- Check all connections are secure
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- Verify serial port is enabled: `sudo raspi-config`
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- Check device path: `ls -l /dev/serial*`
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- Try different baudrates: 9600, 19200, 115200
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- Check user permissions: `groups` (should include `dialout`)
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### Printer prints garbage
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- Wrong baudrate - try 9600 or 19200
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- Wrong wiring - swap TX/RX if needed
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### Pi reboots when printing
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- Power supply insufficient - use external 5V PSU for printer
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### Permission denied
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```bash
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sudo usermod -a -G dialout $USER
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# Log out and back in
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```
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## Next Steps
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Once the test print works:
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1. Note the working device path (`/dev/serial0` or `/dev/ttyAMA0`)
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2. Note the working baudrate (likely 19200)
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3. Update these in your AutoKanban `app/main.py`
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4. Set `DEBUG_PRINT_TO_IMAGE = False` for real printing
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