HW1: The Arduino UNO board
First of all we have to know that there are different kind of the Arduino boards, I will talk about Arduino UNO board, which is the most common for beginners. Arduino is an open project, anyone can build his own board compatible with the original one and infact you can find many clones sold on internet.
Because of that, your board could look a bit different from the one I’ll show you in my articles, but don’t worry all the most important things will be in the same place and you will have no problem to follow what I write.
Let’s take a look to the board:
as you can see I’ve marked some sections of the board.
Group 1: these are the power pins
- 3V3 is a 3.3V output, this is not often used, but some components could require that voltage to work.
- 5V is a 5V output, we will use this one to power our project, at least the first ones.
- GND are ground pins, here we will connect the ground of our projects.
- VIN has two uses, we can use it to supply power to the board from an external source such as a battery or a wall adapter, or we can use it as regular power source, the voltage provided depend on how the borard is plugged to a power source, if we are using a 9V battery or 9V wall adapter we will have 9V flowing from the VIN, while the other pins will go on supplying 5V and 3.3V.
Gourp 2: Analog Input pins
These pins in most cases are used to acquire data from analog sensors such as: temperature sensors, light sensors, proximity sensors and so on. If needed they can also be used as digital outputs, but we don’t need that kind of use now. Analog pins can read a range of values based on the voltage which arrives to them, this range is usually 0 to 1023, but it is possible to verify that and we will see how when we will talk about components connected to those pins.
Group 3: Digital pins
These pins are both for input and output and they are those which we will want to use to interact with components like LEDs, motors, LCD displays, buttons and so on.
As digital pins they can receive and send only 2-states signals which correpsonds to the presence (1) or absence (0) of current. When the digital pins are used as output, they supply 5V.
You can notice that the digital pins are numbered from 0 to 13, but some of them have an additional character next to them, in the picture the character is a ~ (tilde), but on other boards there could be a different character, usually a # (hash), anyway the pins marked with an additional character are special, they are called PWM (Pulse-Width Modulation).
PWM pins are digital pins which can simulate an analog output. To do so, a sequence of alternate 0 and 1 are sent to the connected component, more or less quickly depending on which kind of behaviour we want to obtain.
Pins 0 and 1 also have another tag next to them: RX0 and TX0. That means that they can be used to send and receive data from/to Arduino using a serial port, but we will not do that, we will use the USB port instead, so think to those two pins as regular digital pins.
In this group there is an additionl ground pin, it has the same funcionality as those in group 1.
Group 4: LEDs
These could have a different position depending on the board, but usually that’s the place.
TX and RX say when Arduino is sending and receiving data, you will notice them blinking while loading a new sketch.
The L LED is connected to the digital pin 13, that means that any time you will send a signal from that pin, the L LED will light up. That hasn’t really a use, but it will allow us to write and execute our first sketch, I will write it in the next article, where I will talk about how to write the code and to load it into the board to be executed.
There is also another LED, it is named ON and it is lit up when Arduino is connected to a power source.
You can see other things on the board, in example the pins named ICSP, they are used to program Arduino from an external programmer, useful if there is not a bootloader already installed on the board’s microcontroller, but it is not our case we will do everything through the USB port.
The reset button could be found in different places, its function is the same as the reset button on a desktop computer, it reboots the board, it doesn’t delete anything.
AREF is used as a reference pin to compare two voltages for more accurate readings, but that’s a bit advanced at the moment for us.
RESET pin is used to send a reset signal to the board from an external button in place to use the one on the board itself.
IOREF pin is another pin used as reference.
In the next article we will see a first working project using Arduino.