Isolated USB to UART Converter for Arduino pro mini

It ‘s an inexpensive USB port saver! Simple, tiny USB to UART converter with digital isolator working between 2.5V and 5V up to 3Mboud.

We have launched this project as kickstarter campaign:


There are many types of cheap USB – Serial converters on the market, but sometimes they have some issue with drivers since they use fake chip.
So we had decided to make our version of USB – Serial converter, plus we added a digital isolator. The first project was the Debug Board, and later we made this new variant.


It’s a USB to UART converter with a digital isolator at the UART side.
It has a micro USB for connecting to the PC and a 6 pin header with the same pin-out of the Arduino Pro mini board.

The chip FT231XQ is used as interface between the USB and the UART protocol, while the Si8642 is used for isolate the board from the PC.
This converter is very useful if you are working on some projects and worrying about short circuit with the main power supply. Because the isolator isolates the two sides therefore there is no electrically connection.


  • You don’t burn your PC in case of some accidents between your project and the main power supply. Check our test!
  • The noise from your PC doesn’t enter in your project.
  • Your project and the PC have isolated ground.
  • Voltage levels of the UART are the same of the power supply of your project.
  • Your project is not powered from the USB of the PC, so you don’t have power issue when you power off your project.

Technical data

  • Original FT231XQ: Compatible with almost all the operating systems and capable of variety baud rates from 300 baud up to 3 Mbaud
  • Original Si8642BB-B-IS1: Low-Power Quad-Channel Digital Isolators with isolation rating up to 2.5kV
  • Size of 40 x 17 mm
  • 4.1 mm isolation between the two sides guarantee an electrical isolation up to 1kV
  • Working between 2.5V to 5V.
  • TX and RX LEDs indicators.
  • Micro USB connector.
  • Standard 2.54mm 6 pins female header.
  • Protected by a transparent heat shrink sleeve.



#NameDescriptionDirectionVoltage level
2CTSClear To SendInputSame of +
3+Power SupplyInput2.5 - 5V
4TXTransmitted DataOutputSame of +
5RXReceived DataInputSame of +
6DTRData Terminal ReadyOutputSame of +

Project File

Schematic and PCB layout are available on my CircuitMaker account.

This product is ALIVE by getting funded 150% of our target!!

It’s available in our Tindie store, you can order this product directly from Tindie.
Check out our experiment with the main power supply: 

You can purchase this item in our Tindie and eBay stores: