Arduino Pro Mini CP2102: Flash and read serial | ShillehTek

May 15, 2026 22 views

Project

Flash an Arduino Pro Mini with a CP2102 USB-to-TTL adapter, then read Serial output for fast debugging on USB-less boards, with parts from ShillehTek.

15 min Beginner2 parts

Project Overview

Arduino Pro Mini + CP2102 USB-to-TTL: Use a CP2102 USB-to-UART serial converter to flash an Arduino Pro Mini (and other USB-less targets like ESP-01 or bare MCUs) and read Serial output over a COM/tty port.

Time: ~15 minutes
Skill level: Beginner
What you will build: A CP2102 wired to an Arduino Pro Mini, flashing Blink and reading Serial output.

CP2102 USB-to-TTL serial converter module used to flash USB-less microcontrollers — CP2102 - the workhorse USB-to-UART bridge.

Parts List

From ShillehTek

CP2102 6-Pin USB to TTL UART Module - USB-to-serial bridge for flashing and Serial console access
120 PCS Dupont Jumper Wires - quick, reliable wiring between the CP2102 and your target

External

A target device without USB (Arduino Pro Mini, ESP-01, bare ATmega328P)
CP2102 driver for your OS (Windows / macOS need the Silicon Labs VCP driver; Linux is automatic)

Note: Match the target’s logic level. The CP2102 has a jumper / solder pad for 5 V vs 3.3 V on TX/RX. Wire your target to the right setting before powering up.

Step-by-Step Guide

Step 1 - Inspect the Module

Goal: Identify the CP2102 pins you will use for power, UART, and optional auto-reset.

What to do: Locate the 6-pin header and confirm which pins are VCC, GND, TX, RX, DTR, and RTS on your specific board revision.

CP2102 USB-to-TTL module showing USB-A connector and 6-pin header for VCC GND TX RX DTR RTS — USB-A on one side, 6-pin header on the other: VCC, GND, TX, RX, DTR, RTS.

CP2102 pinout reference highlighting TX RX and DTR for Arduino Pro Mini programming — DTR is the magic line for auto-reset on Arduino Pro Mini uploads.

Expected result: You know exactly which CP2102 pins to connect to your target.

Step 2 - Install the Driver

Goal: Make the CP2102 appear as a COM/tty serial port on your computer.

What to do: Download the “CP210x USB to UART Bridge” driver from Silicon Labs for Windows or macOS. Linux ships with it. After install and reboot, plug in the CP2102 and confirm a new COM/tty port appears.

Expected result: You can select the CP2102 port in your flashing tool (for example, Arduino IDE).

Step 3 - Wire to Your Target

Goal: Connect power and UART lines correctly between the CP2102 and the target board.

What to do: Wire VCC and GND, then cross the UART lines (TX to RX, RX to TX). If you want auto-reset for Arduino uploads, also connect DTR through a 100 nF capacitor to the target’s reset/DTR line.

CP2102 wired to an Arduino Pro Mini on a breadboard with TX to RX RX to TX and power and ground connected — Cross TX/RX: CP2102 TX to target RX, CP2102 RX to target TX.

CP2102 5 V to Pro Mini VCC
CP2102 GND to Pro Mini GND
CP2102 TX to Pro Mini RX
CP2102 RX to Pro Mini TX
CP2102 DTR to Pro Mini DTR (via 100 nF capacitor for auto-reset)

Expected result: Your Pro Mini (or other target) has power and a working UART connection to your computer.

Step 4 - Auto-Reset Mod (Optional)

Goal: Enable one-click uploads by letting the IDE toggle reset automatically.

What to do: Add a 100 nF capacitor between DTR and the target’s reset line (as shown). Without the capacitor you may need to press reset manually during uploads.

100 nF capacitor mod between CP2102 DTR and Arduino Pro Mini reset line for auto-reset during uploads — A 100 nF cap between DTR and the target’s reset gives one-click uploads.

Expected result: Uploads reset the board automatically, similar to an Arduino with built-in USB.

Step 5 - Upload and Read Serial

Goal: Flash a sketch and verify Serial output over the CP2102.

What to do: In the Arduino IDE choose the matching board (Pro Mini, 5 V/16 MHz), select the new COM/tty port, and click Upload. Then open Serial Monitor.

Arduino IDE Serial Monitor showing output from an Arduino Pro Mini flashed using a CP2102 USB-to-TTL adapter — The flashed sketch’s Serial output comes back through the CP2102.

Expected result: The upload completes successfully and the Serial Monitor shows output from your sketch.

Step 6 - Where to Take It Next

Goal: Apply the same CP2102 workflow to other USB-less boards.

What to do: Use the CP2102 to flash and talk to other targets that expose UART.

Flash an ESP-01 in bootloader mode (GPIO0 to GND on boot)
Talk to a bare ATmega328P running the optiboot bootloader
Debug an STM32 over its UART when you don’t have an ST-LINK handy
Use the CP2102 as a logic-level UART probe for any embedded project

Expected result: You can reuse the CP2102 as a general-purpose flashing and UART console tool across multiple projects.

Conclusion

The CP2102 USB-to-TTL adapter is a simple way to flash and debug USB-less targets like the Arduino Pro Mini, ESP-01, and bare MCUs. With TX/RX wired correctly and (optionally) a DTR capacitor for auto-reset, you can upload sketches and read Serial output reliably.

Want the exact parts used in this build? Grab them from ShillehTek.com. If you want help customizing this project or building something for your product, check out our IoT consulting services.