Dual RS232 to USB Converter

Very simple, pendrive size, zero programming double RS232 via USB

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Today's PC's rarely have RS232 ports. If they do, they are most likely internal placed on the motherboards. Laptops only have them through docking stations.
Some companies on the market offer RS232 to USB adapters but they offer only one serial port in an acceptable price. This project contains an old FTDI chip (FT2232D), but thanks to its default config it doesnt need to be programmed and works as dual uart adapter right after its soldered on the board. Its also very size sufficient- it fits into laptops USB port even when theres a pendrive next to it.

The board contains minimum amount of elements only to get 2 uart ports running. The only signals connected are TX, RX and GND as the other old pins are never used these days anyways. This project is a great deal if one application uses more than 1 serial port (For example traces and bootloader).

Many different cables can be made for this board depending on the application, for example a standard DB9 male one.

In the future I am considering trimming it a bit:
- Getting rid of the USB A plug and create a USB plug shaped from PCB instead. That would also allow me to drop protection resistor and capacitor.
- Making the board more narrow and placing components on both side of the PCB.

The PCB is easily placable in a thermo-tube so no need for the casing.

2 boards were already soldered and tested. They work without any problems.

  • 1 × FT2232D Microprocessors, Microcontrollers, DSPs / USB Microcontrollers
  • 1 × MAX202 Application Specific ICs / Telecom ICs
  • 1 × USB A plug
  • 1 × Resistors and capacitors [0603]
  • 2 × MX-53261-0371 Molex connectors

View all 6 components

View project log

  • 1
    Step 1

    Firstly, solder the FT2232D chip as it is the hardest to assembly. Its pitch is very dense and if the board you are using has been made using HAL there might be to much solder on the pads. You might want to take it off.

  • 2
    Step 2

    After that the passive components first, that is (mostly 0603) resistors and capacitors.

  • 3
    Step 3

    Solder MAX232, Oscillator and  connectors.

View all 3 instructions

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OneShot Willie wrote 02/09/2018 at 10:12 point

DTR and RTS stand for Data Terminal Ready, and Ready To Send. It's used to control the flow of data between two devices. Think of DTR as "hey I'm ready" and RTS as "Here it comes..." signals for serial communications. So if we were to think negatively, DTR is a hold off signal (wait a minute) and RTS is a busy signal.  Ifn I remember correctly, these signals were called flow control signals.

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Łukasz Przeniosło wrote 07/29/2014 at 05:39 point
Hi there,
I didnt know that is the way arduino bootloader works with the pc through RS232. Always thought it is based on timeouts, i have never used arduino software though. In my whole carrer i havent used those additiobal pins once, and I create loads of apps basing on serial communication, including bootloaders or loggers of any kind. You dont need those pins to printf() to console ;).

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Łukasz Przeniosło wrote 07/29/2014 at 05:41 point
But on the other side, those pins could be added if the board is rebuild a bit- it can still be space sufficient.

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kc8rwr wrote 07/25/2014 at 16:02 point
"The only signals connected are TX, RX and GND as the other old pins are never used these days anyways"


The DTR pin is very useful if you want to program an Arduino.
Both DTR and RTS are useful if you want to use a computer to turn something on/off. For example, they are both commonly used for switching a transmitter on/off for digital ham radio modes.

Maybe those are kind of special interest purposes but this is RTL-232 Serial. That IS a special interest purpose at this point! What else is it used for, really old printers?

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