Turn an Arduino Uno into a LPT/DB25 parallel port emulator. Data received via the parallel interface is forwarded over USB Serial (or WiFi on R4) to a browser-based interface for real-time visualization and printing.
No parallel printer required. Works with old DOS apps, legacy software, and educational setups.
- Upload LPT_Emulator/LPT_Emulator.ino via Arduino IDE (115200 baud).
- Open web_interface.html in Chrome or Edge.
- Click Connect and select the Arduino COM port.
| DB25 | Arduino | Signal |
|---|---|---|
| 1 | D2 | STROBE (INT0) |
| 2–9 | D3–D10 | D0–D7 (data) |
| 10 | D11 | ACK |
| 11 | D12 | BUSY |
| 13 | D13 | SELECT |
| 18–25 | GND | Ground |
Use 5V TTL levels only. See PINOUT.txt for full diagram.
The R4 WiFi is fully supported with the same wiring. To use WiFi:
- Upload the firmware to the Uno R4 WiFi.
- Open web_interface.html, go to Settings → WiFi and enter your network credentials (SSID and password).
- Click Connect — the interface discovers the board automatically or you can enter the IP manually.
| Uno R3 | Uno R4 WiFi | |
|---|---|---|
| CPU | ATmega328P 16 MHz | RA4M1 48 MHz |
| RAM | 2 KB | 32 KB |
| Connectivity | USB | USB + WiFi |
| Command | Action |
|---|---|
V |
Firmware version |
S |
Buffer usage |
R |
Reset buffer |
? |
Help |
- No connection: check COM port, reset board, re-upload firmware.
- No data: verify STROBE is on pin D2, check wiring and GND.
- Garbled text: try CP‑437 encoding (DOS apps) in the web interface.
- WiFi not found: confirm credentials, check Serial Monitor for IP.
MIT © 2026 LPT-UNO Project