USB-to-Serial converters are some of the most used modules on my bench. I have quite a few of them, most of them are the cheap online type that can be had for a few dollars.

As part of my new project, where I am seriously looking for an alternative chip to replace the ATMEGA328, which has become almost impossible to get, and super expensive when you do get it, I needed to get hold of a UPDI programmer.

There are many available online, from cheap to more expensive, but I wanted to build my own, as it did not seem too difficult to do.

As another part of my daily tasks, I also use a lot of ESP-type chips, which have a particular procedure to upload code via an external serial adapter.

The idea was thus to design a USB UART module that has multiple purposes, as well as being easy and cheap to assemble.

Be able to program ATMEGA328 Chips via Serial

Be able to be used as a standard USB-to-UART adapter

Be a UPDI programmer

Have a selectable target voltage between 3.3v and 5v

Have all modem signals (RTS, CTS, DSR, DTR) broken out.

Be able to auto-flash and reset an ESP32 or ESP8266 device, or similar

Breadboard Prototype Multipurpose USB-to-UART/UPDI Programmer

What is on the PCB?

The PCB is powered by the PC USB port. The target device voltage is selectable between 3.3v and 5v. The device mode can be changed from UART to UPDI mode with a jumper. An additional header specifically for ESP32/ESP8266 devices is provided, giving access to the FLASH and reset signals for the ESP device.

The USB to serial conversion is taken care of by a CH340G Chip, which provides all the relevant modem signals as well.

All signals, with the exception of the "RING" signal, are broken out onto the main header.

Note that there are NO status or POWER LEDs on the board. This was on purpose, as these sometimes interfere with the UPDI programming mode.

Prototype PCB - Assembled

PCB - Top

PCB - Bottom

Connecting to different devices

ESP32 or ESP8266 Devices

When in UART mode, the device can be used to upload code to an ESP32/ESP8266 automatically, similar to a standard dev board, without requiring you to press and flash and reset buttons.

This is achieved by connecting the device as follows:

UART MODULE SET to 3v

UART VCC to ESP 3v

UART GND to ESP GND

UART RX to ESP TX

UART TX to ESP RX

(Connections for Auto Upload/Reset)

UART RST ( on ESP-Flash Header) to ESP RST

UART GPIO0 ( on ESP-Flash Header) to ESP GPIO0

It will now be possible to flash and auto reset the connected ESP device from the Arduino IDE, and possibly others as well...

Arduino (Atmega 328P)

In the current version of the prototype, you have to connect it as follows:

UART Target voltage set to 3v or 5v depending on what type of board you are uploading

UART Tx to Arduino Rx

UART Rx to Arduino Tx

UART VCC to Arduino 3v or 5v ( depending on the target voltage required by the board you are flashing)

UART GND to Arduino GND

To allow for auto flash/reset on the Arduino, a 100nf capacitor is required between the UART DTR line and the Arduino Reset pin. This capacitor has NOT yet been fitted onto the PCB, as I usually use ICSP to upload these. Future versions of the PCB shall have this included.

ATMEGA4808/4809 and or ATTiny with UPDI Interface

This device is currently an LV-only UPDI programmer. Connections are as follows:

Set Target voltage on J1 of the UART/UPDI programmer.

Set The Device mode on J2 to UPDI mode

Connect VCC and GND from the Programmer to the target chip/board

Connect Programmer UPDI pin( shared with RxD) to Target UPDI pin.

General use UART for use as Serial monitor/Terminal

Set target voltage on J1

Set device mode to UART on J2

Connect VCC, GND from UART to the target device,

UART Tx to Target Rx

Uart Rx to Target Tx

Optionally connect required modem signals, RTS, CTS, DTR, and DSR as needed