How to Program an Arduino Pro Mini with an Uno

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In this step-by-step tutorial, we will show you how to program your Arduino Pro Mini using the Arduino UNO. As the name suggests, the Pro Mini is smaller than, say, the Arduino Nano board.

It is important to note that the Pro Mini does not have an onboard programmer or USB port for programming. 

You need to have the relevant programmer, such as FTDI, to complete the process. The other option is to use the Arduino Uno, which we will do, in our step-by-step tutorial below.

How to Program Arduino Pro Mini with Uno

The main difference between Arduino Uno and Arduino Pro Mini is the size. At about 1/6 the size of the former, it does not compromise on its functionality. You get certain benefits such as more space-saving capacity when you are, for example, working in small enclosures.

It will also work well for lightweight or small projects. At 8MHz, you get sufficient space for your projects and enough microprocessor power. You get as much functionality and control over your projects as you would if you were using the Arduino Uno.

What makes the Arduino Pro Mini popular is that they are relatively inexpensive. If you buy them from some online platforms, you can get them for as little as $2. You can embed it into your project permanently, and you’ll enjoy the savings resulting from low energy consumption.

Before embarking on programming Arduino Pro with your Arduino Uno, take the time to familiarize yourself with the different components. It is especially critical if you are new to this. You will get to avoid mistakes, especially where connections are concerned.

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So let’s get into our tutorial on how to program Arduino Pro with Uno. 

Method 1 

In this first method, you will need to remove the microcontroller from the Arduino Uno. The mini Pro, due to size limitations, does not have a USB to serial converter. You also miss out on the connector, which is why you will have to get it from the Arduino Uno.

You will need the following:

  • Arduino UNO DIP. We need to use the DIP version because you cannot use the SMD one for this project. 
  • Arduino Pro Mini. You can go for a 3.3V or 5V pro mini. Simplify your work by ensuring that you solder the header pins in place before starting your project. If you lack soldering skills, you will find some fantastic tutorials online.
  • LED
  • Breadboard that comes complete with jumpers
  • Flat-head screwdriver

Removing the ATmega 328 IC

Before you start any connections, you will need to remove the ATmega 328 IC from the Arduino UNO. It is a delicate process; otherwise, you could end up damaging the components. 

Follow the steps below:

  • Take your flat head screwdriver
  • Take note of the direction the half-circle on the IC is facing. You will need this information when you are assembling the unit, once you finish the programming.
  • With a steady and careful hand, place the screwdriver under the IC.
  • Using gentle motion, use side to side movement to dislodge it from its socket. You will need to do it on both sides. If you do it correctly, it should pop out without any issues.

You are now ready to start the connections.

Establishing wire connections

This second part of the tutorial is not difficult and should not take you a long time. 

Take your Pro mini-board. Make sure that you have soldered the headpins into position correctly.

Follow the guide below on how to connect the wires. 

  • The Uno 5 or 3-volt wire connects to the Vcc on the Mini Pro
  • The Uno GND connects to the corresponding GND on the Mini Pro
  • The Uno TX connects to the corresponding TX on the Mini pro. This should be Pin 1 on the Mini.
  • The Uno RX corresponds to the Mini RX or Pin 0
  • Connect the Uno reset to the Mini Pro DTR

If you have not programmed your Pro Mini, all you need to do is swap the RX and TX pins. 

If you follow the steps above carefully, that is all you need to do to establish the connections. 

Uploading Code to the Pro Mini

Take the following steps to upload code to your pro-mini

  • Start by connecting the Arduino Uno to your computer
  • Open up the Arduino IDE software on your PC 
  • Now go to tools > Boards > Arduino Pro Mini
  • For the next step, go to tools > Processor > choose the processor. Since we are using Atmega 328p, this is what you will choose. 
  • For the final step to uploading code: tools > port > select Arduino Uno com port.
  • If you want to know whether you have been successful in uploading your code, use your LED. Use Pin number 13 to connect your LED to your Pro Mini. 

Disconnect the Pro Mini from the Uno, and if you wish, use it as a standalone controller. 

Method 2

Method two eliminates the need to remove the microcontroller from the Uno. 

When establishing the connections, use the steps we have highlighted above. The only difference is:-

  • You must establish a connection between the GND and reset the PIN on your Arduino.
  • You must also disconnect the DTR pin wire from your Pro mini. 
  • During the process of uploading code, ensure you press the reset button on the Pro Mini Arduino. You must be very precise in getting the timing right; otherwise, you will not succeed in uploading the code. If you are new at this, you are better off going with method one for higher chances of success.

Final Thoughts

We have looked at the steps you need to take when programming your Arduino pro mini using Arduino Uno. The critical components are ensuring that you make the proper connections and that you upload the code correctly. 

We have proposed to simplify the steps as much as possible, even going a step further to give you two options. Choose the one that works for you, and enjoy the use of your Arduino Pro Mini. 

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