The Arduino Pro Mini packs the full ATmega328P into a tiny board — but it has no USB port. To upload code, you use an external FTDI (USB-to-serial) adapter. Here's exactly how.
Why no USB?
Dropping the USB chip keeps the Pro Mini small and cheap — ideal for permanent installs. The trade-off is you need an FTDI adapter (a one-time buy) to program it.
The 6-pin programming header
The Pro Mini's serial header has six pins. Match them to your FTDI adapter:
| Pro Mini | FTDI adapter |
| DTR | DTR |
| TXO | RX |
| RXI | TX |
| VCC | VCC |
| GND | GND |
| GND (BLK) | GND |
Note that TX and RX are crossed — the board's TX goes to the adapter's RX and vice-versa.
Match the voltage
Pro Minis come in 5V/16MHz and 3.3V/8MHz versions. Set your FTDI adapter's voltage jumper to match your board, or you risk damage or failed uploads.
Upload steps
- Wire the FTDI adapter to the 6-pin header as above.
- In the Arduino IDE, choose Tools → Board → Arduino Pro or Pro Mini.
- Select the correct processor (ATmega328P 5V 16MHz or 3.3V 8MHz).
- Pick the FTDI adapter's COM/serial port.
- Click Upload. The DTR line auto-resets the board so the sketch flashes.
Common problems
- “not in sync” error: TX/RX are probably swapped — cross them.
- Upload fails: check the processor/voltage selection matches your board.
- No port shows: install the FTDI/CH340 driver for your adapter.
Need a Pro Mini or an FTDI adapter? We stock them with Bengaluru dispatch and GST invoice. WhatsApp +91 78285 34155 for help.