Serial Port Mini RS232 to TTL Converter Adaptor Module Board MAX3232 with Arduino

So I buy 5 of these little things when I find out I am dealing with RS232 device instead of a TTL device.  They arrive quick and I am delighted only to find I dont quite know how to wire them up.  The project is to use an Arduino – which I love dearly – to drive an LED rolling display. I am not an electronics expert – so I struggled a little and popped 2 of them good and proper..

Never mind.  I’ll buy this instead

I am as always standing on the shoulders of giants –


So my experience is:

From the RS232 Port – RX, TX and GND.  Thats the -> -<and the – signs.  Easy enough


-> RX

<- TX

On the TTL (Arduino)  side – DO NOT USE 5V use 3.3V as this toasts the device and heats up and like tops itself.  It certainly got very toasty when I put 5V across it.  This could be because I messed up somewhere in the wiring but it certainly works well for me.  I can also use the SoftwareSerial library as well so I don’t need to use TX/RX on the TTL Serial pins 0 and 1

So TTL is


-> – PIN X

<- PIN Y

For my device I used PIN 0 and PIN 1 – TX/RX – but I guess you can use other pins.

TTL RS232 Pinouts

TTL RS232 Pinouts



Hope this helps – it does work!


22 thoughts on “Serial Port Mini RS232 to TTL Converter Adaptor Module Board MAX3232 with Arduino

  1. I tried to attach arduino nano with this converter to PC, but attached vcc 5V. Am I burned the converter? Or if I attach vcc 3.3V from Arduino board it will work properly?

    • I connected mine to 5V – it went very hot and I unplugged it. I then put the 3.3V on and it worked. So I guess it depends on how long the 5V is connected to VCC.

  2. Thank you for your answer. And when it was hot there was no communication between device and arduino (in my case there was no communication between PC and arduino no RX no TX)? I’ll cross my fingers and try to connect 3.3V. If it won’t work I’ll make a simple schematic using 2 transistors

  3. This will be long solved now however something came to mind which may be of assistance.

    I don’t know if the Arduino has +/- 5V available however the BBC micro came with an “rs232” port which used +/- 5V instead of the official 12V. It interoperated satisfactorily with real rs232 devices such as IBM PC. It also did not melt itself when offered +/- 12V:-)

    I came across Daxcad when doing PC support years ago.

  4. Hi Davy,

    It’s a nice site you have 🙂

    Will it work if the rs232 data is +/-12V. I know the max232 chip is able to deal with it, but is the board able to support it ?
    One side of the board will be +/-12V and the other side of the board will be +/-3.3V or even +/-5V.

  5. I am using this to connect an Arduino Mini (newest version) to a PC serial port header. I want to know if I can program over this or do I need to connect the DTR pin somewhere?
    Or do I program by pressing reset button at a certain time?

  6. Hello!
    I used your scheme to connect my arduino Uno and ttl – rs232 converter. So, I connected arduino to my PC using rs232. But I`m not sure that it work correct. I can`t load any code on arduino. I received this error avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00
    What it could be?

  7. Hi,
    Thanks for you post, very helpful!
    I’m trying to connect rs232 enabled barcode scanner, to Arduino Uno, (I know I can connect it with USB host shield, but I prefer the simple rs232 connection.)
    I bought the PCB with the max3232 chip, connected the TX Rx gnd and vcc of Arduino to the TTL side, and the serial barcode TX Rx, (gnd to minus, vcc to plus) to the rs232 side.
    I tried to read the serial in the Arduino code, but received nothing…
    I must add that I connected also more power to the barcode scanner, and the device turned on, so it seems that I missed some initialization code to the RS232 protocol, or something, can you tell what do I need to start to do in the arduino code?

    • Hi Moshe, I too am trying to connect a barcode scanner to Arduino with max3232 converter. Are you able to get it to work?

  8. This circuit, RS232 TTL, does not have MAX3232 pin 11 connected to VCC or ground,
    so it oscillates and is overheating !
    Put a wire between free + hole(VCC) and pin 11 .

    • Pin 11 on the MAX3232 is the T1N and should be connected to the TxD. Why do you say there should be a VCC connection to pin 11 ?

      My Converter doesn´t work and is also getting warm with the arduino 3.3V ! Is there something i forgott ?

  9. Hi, I’m struggling with this mini board too, as a first test I put LEDs on both tx sides to “see” the data, but I think the top side of the board is isolated from the bottom, so I wired the tx top with tx bottom and so on. However still not working. I will try the 3.3 volts source.

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