Arduino ProMini , as the name indicates , is a miniature version of UNO .It runs on 16 MHz crystal ,ATMEGA328 ,but lacks USB connectivity. There are 5V  (16MHz) & 3.3V (8MHz) versions. In this demo I use the 5v version.




There is a voltage regulator on board so it can accept voltage up to 12VDC. If you’re supplying unregulated power to the board, be sure to connect to the RAW pin and not VCC.

Vcc accepts only 5v.

The latest version of this board breaks out the ADC6 and ADC7 pins ,also adds footprints for optional I2C pull-up resistors.

To upload code on to pro mini , a USB-TTL adapter is required.There are many types of  USB adapters available.The most reliable one that works up to Windows 10  is the one built on CP2102 IC .

CP2102 adapters are available in 2 variants .One with 6 pins that include the DTR  , Data Terminal Ready , which handles the RESET required by the promini board.

The other board is commonly available one with 5 pins.Here RESET must be done manually on promini while code is uploaded.






First let us upload code using the 6 pin version .

The connections are

PROMINI                USB-TTL

DTR   —–>   DTR

TxO   —–>  Rx

RxI    ——> Tx

Vcc   ——> 5v

GND  ——> GND

In some Promini boards the DTR pin is printed as GRN.


Plug in the USB board to PC & open the Device Manager . If the driver is installed previously , a COM port will be allotted.Otherwise , download the silicon labs cp2102 driver from here & install.


Image 1

Open the Arduino IDE , feed in the COM port allotted.

Select Board as Arduino Pro or Pro Mini , Programmer as USBasp.

In newer versions of IDE there is option to select type of ProMini board.Under Processor select ATmega328 5v,16MHz

Image 2

From Examples open the BL;INK sketch

Image 3

Click on UPLOAD button.

The DTR pin of USB board takes care of the RESET  & your code will be uploaded to PROMINI without any manual reset.


Image 4

Uploading code using a 5 pin version , needs a manual RESET on PROMINI.

The connections are

PROMINI                USB-TTL

TxO   —–>  RxD

RxI    ——> TxD

Vcc   ——> 5v

GND  ——> GND



Plug in the USB to PC & note the COM Port allotted.

Open Arduino IDE .Feed in the COM port , select board as Arduino Pro or Promini & Programmer as USBASP

From Examples , open the BLINK Sketch

Image 2.1

Click on UPLOAD button.

Image 2.6

Watch out for the message at the bottom of IDE.

“ Compiling Sketch “ message appears first.

Then it changes to “Uploading”

Image 2.2

As  soon as you see “Uploading” message , gently press the RESET Key on Promini.

This should be done instantly , as soon as you see “UPLOADING” message.

Image 2.3



If the KEY Press is at the right time , your code will be uploaded successfully.



You can also use your UNO board to upload code on Promini.

To use the UNO board , you need to by pass the bootloader .For this  upload an empty code to UNO or connect the RST pin to GND

Connecting RST pin to GND bypasses the bootloader & only the serial converter IC located near the USB socket is used as USB-TTL.

The connection here is STRAIGHT & not reverse

Tx of Arduino UNO goes to Tx of Promini

Rx of UNO goes to Rx of Promini

Gnd to Gnd



Connect the USB cable to PC & open the IDE.

Select the port where UNO is connected.

Image 2.5


Select the board as Arduino Pro or ProMini

Image 3.1

Open the BLINK sketch & UPLOAD.

Watch out the message at the bottom of IDE.

Initially “Compiling Sketch “ appears.

Then the message changes to UPLOADING…


Image 6

Once you see UPLOADING… message  , press the RESET key on PROMINI.




The code is now Uploaded successfully.

Image 7

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