A useful and simple IO Shield for Arduino
In order to “visually” highlight the behavior of Arduino programs you must connect a device to the I/O pins, which gives you tangible signals. Normally, if you want to check if a program changes a level of an output pin, answering a command or executing a check routine, or event, you must check it by measuring the voltage level on the pin with a voltmeter. But if we connect this pin to a LED with the correct driver circuit, we can check the behavior of the program thanks to a switch in the LED state: it could be on, off, or partially on, if you connect it to an analog output pin. In a similar way, if the output pin is connected to a relay, we can drive external loads with ease. The same applies to the digital or analog input pins, and analog outputs.
To give a more professional appearance to our projects and to further ensure the reliability of the connections we prepared a experimentation shield in “Arduino” style, indicated mostly for Arduino YUN (but that can also be used with earlier versions).
To give maximum flexibility to the use of the shield, all external connections are mounted on screw terminals. The shield provides six digital outputs connected to as many LEDs to display the status plus relays to activate external loads. You can connect LED strips, cooling fans, buzzers or whatever you prefer. There are also six analog and six digital multifunction inputs three of which can be used as PWM or DAC analog outputs if you prefer (pin 3, 5 and 6.)
The board requires a separate power supply of 12 volts if it is used with Arduino YUN, or it can get power directly from Arduino UNO.
As you can see in the circuit diagram the shield is divided into sections. Each section is specialized in bringing outside the possibility to connect to a specific type of I / O pin. Within each section of the circuit diagram is repeated identically for each of the pins.
Let’s start from the section that serves the digital output pins, which correspond to Arduino pin 8, 9, 10, 11, 12 and 13.
In this section each pin drives a transistor driver circuit coupled to a relay. On the screw terminals all the terminals of the relay are available, the central terminal C, the “normally closed” NC terminal and the “normally open” NO one. The arrangement of the ends on the terminals is visible in the ” Mounting Plan”.
For more detail: A useful and simple IO Shield for Arduino