Arduino UNO Schematics

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In this post I will discuss about the schematics of the Arduino UNO microcontroller development board. In the previous posts I have discussed about the introduction and basics of the Arduino UNO, Arduino MEGA and Arduino PRO MINI. In this post I will discuss about the circuit design of the Arduino UNO development board.

After reading this post the reader will learn about the hardware design of the Arduino UNO, the reader will learn about the ATMMEGA328p microcontroller IC which is the heart of the Arduino UNO board. The reader will learn about the basic ICs that are used in conjunction with the microcontroller in order to make the board operational. I will discuss about each chip available on the Arduino UNO board. So sit back, keep reading and enjoy learning.

Arduino UNO:

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Before dive into the discussion on the Arduino UNO hardware let us first learn about the basics of the microcontroller board and see why do we need to know the circuit design of the Arduino? So, basically the Arduino UNO is the open-source microcontroller development board based on the ATMEGA328p microcontroller IC. By open source it means that all of the software requirements and the libraries are available on the internet to download and any one can access these libraries and contribute by adding the additional featurs to any library. Besides the software side the Arduino UNO manufacturers have also publicized the hardware design of the Arduino UNO microcontroller development board. So any one can copy the circuit and develop their own microcontroller development board. So it is useful to learn about the hardware of the Arduino UNO and learn about the ICs employed in the schematics of the Arduino UNO. It is important to note here that the Arduino UNO is the development board, which means that Arduino UNO is the plug and play module. Anyone who wants to learn the programming and the hobbyists who want to design their embedded system can employ the board in their design without any effort of designing the circuit for the ATMEGA328p microcontroller as everything from programmer to voltage regulator is available on board. So all you need is to plug your Arduino UNO into the laptop or computer and begin programming. So I will discuss the design which makes the Arduino UNO plug and play module.

Arduino UNO Components list:

Let us now see the components which comprise the Arduino UNO board. The list of the ICs and connectors that are used in the Arduino UNO design is given below:

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  • ATMEGA328P microcontroller.
  • ATMEGA16U2MUR USB to UART Bridge.
  • 5V voltage regulator.
  • 3V voltage regulator.
  • Light Emitting Diodes.
  • 16 MHz Oscillator.
  • USB connector.

Arduino UNO Board Schematics:

The complete schematic of the Arduino UNO is shown as follows:

Note from the schematics that circuit of the Arduino UNO has three main parts that is the microcontroller part which consist of all the peripherals required to operate the microcontroller, USB to UART bridge which converts the data between USB and UART and finally the power portion which consist of the voltage regulators required to power up the microcontroller IC and the Arduino UNO board.

Let us now learn about each of the IC used in the circuit in detail.

ATMEGA328P Microcontroller:

The ATMEGA 328P is the 8-bit, 28 pin microcontroller IC. The microcontroller has 14 digital input / output pins, 6 analog input pins and power pins. ATMEGA328P has one Serial Peripheral Interface computer bus, one Inter-Integrated Circuit computer bus and one Universal Asynchronous Receiver and Transmitter. Out of 14 digital Input / Output pins six are PWM (Pulse Width Modulation) enabled. Note here that all the Digital input / output pins are directly connected to the header on Arduino UNO board. Similarly all of the Analog pins are also connected to the header of the Arduino UNO board. The power pins of the microcontroller are connected to the output of the voltage regulator. The pin description of the ATMEGA328P microcontroller IC is shown in the following figure:

It is important to mention here that the Arduino UNO comes in two forms which are classified on the basis of the package of the ATMEGA328P microcontroller. The ATMEGA328P microcontroller comes in two flat pin package which is SMD (Surface mounted device) and DIP (Dual Inline Package). The DIP package of the ATMEGA328P has total 28 pins whereas the SMD package has total 32 pins. The figure above shows the pin description of the SMD package of the ATMEGA328P microcontroller IC.

The following figure shows the block diagram of the ATMEGA328P microcontroller.

USB to Serial Data Converter:

Another important IC available on the Arduino UNO board without which it is impossible to program and monitor the Arduino UNO is the USB to serial data converter. It is important to note that the ATMEGA328P has three communication buses with the help of which the microcontroller can communicate to the peripheral ICs or I/O devices connected to it. these communication buses are the SPI computer bus, I2C computer bus and UART but the microcontroller has no USB (Universal Serial Bus) interface available, however the Arduino UNO is always programmed using the USB connector available on board. So there should be some in which the data from the computer or laptop that is available in the USB format is converted to the format compatible to the microcontroller thus the USB to Serial data converter serves the purpose here. The pin description of the chip is as shown in the following image:

Notice in the image that the chip converts the USB data into the SPI and UART format which can easily be read by the ATMEGA328P microcontroller IC. The architectural block diagram of the USB to UART Bridge is as shown in the following figure:

The two main ICs employed in the Arduino microcontroller development board are the microcontroller ATMEGA328P and the ATMEGA16U2 USB to UART Bridge, other ICs are the voltage regulators and some of the discrete components that is the diode, LED, resistor arrays etc.

Voltage Regulator:

Let us now learn about the voltage regulator of the Arduino UNO. The Arduino UNO has two voltage regulators mounted on board. One voltage regulator is the 5V voltage regulator and one is 3V3V voltage regulator. The ATMEGA328P microcontroller IC operates at 5 volts which is derived from the 5 volt voltage regulator. The input of the Voltage Regulator gets connected to the power jack and its output is connected to the Vcc pin of the ATMEGA328P microcontroller.

Discrete Components:

The Arduino UNO board also has discrete components such as diodes, LEDs, transistor and resistors.

Type B USB Connectors and Headers:

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The Arduino UNO has type B USB connector for either powering the board or programming the microcontroller as described in the previous section. The headers mounted on Arduino board carries the Digital Input / Output signals, Analog input pins and power pins.

That is all for now I hope this article would be helpful for you. In the next post I will come up with more interesting topics till then stay connected, keep reading and enjoy learning.