IN/OUT shield for Arduino – 6 relays, 6 analogue and digital inputs

* The shield is supplied as a kit to be assembled

Driving the relays and reading the digital signals and the voltages on the analogue inputs can be done with simple software routines or with ready-made generic firmware; you can also work from a personal computer, since the Arduino IDE includes a terminal emulator (a sort of Windows HyperTerminal) that allows serial data to be sent to and received from the board, and therefore the relays and the inputs to be driven straight from the PC. By sending over the serial link (set to 9,600, 8, N, 1, that is 9,600 bps, 8 bits, no parity and one stop bit) the command O followed by the channel number, the corresponding relay is switched; for example, with O2 relay 2 is switched. The outputs are designed to work in bistable (toggle) mode, so every command inverts the state of the relevant relay. With the command Ix (where x is the channel number) you ask for the state of a digital input, while with Ax you query an analogue input.

For every command the Arduino module replies to the terminal emulator with a message giving the state of the output produced by that command, or the state of the input the command referred to. For example, giving the command O2 you may get “Out 2 = 1” . Likewise, for the inputs you can get messages such as “In 3 = 0” for a digital input, or Analog 1=126 for an analogue one; in the latter case the value shown after the equals sign is the corresponding A/D converter reading.

You can also manage the I/O by loading the FIRMATA firmware into the Arduino microcontroller, which can be downloaded from the web pages http://arduino.cc/en/Reference/Firmata or http://firmata.org/wiki/Main_Page . With it you can drive the inputs and the outputs directly from a graphical interface, thanks to Processing; this is a Java-based, open-source programming language that we covered in the fifth part of our Arduino course, published in issue number 151 (November 2010). Processing is a language that lets you build a great many applications (sketches with Arduino) and in this case we can use it to run the firmata sketch, which is found among the examples in the Arduino IDE and which we will use to manage the inputs and the relays on our board. This sketch needs to be modified slightly, simply to “tell” Arduino which pins are connected to the outputs and which to the inputs; after that everything will work without difficulty.

• 6 relay outputs: max 0.5A, 30V
• 6 analogue inputs
• 6 digital inputs
• Stackable design: the shield can be stacked with other shields
• Large community of users
• Requires 1 Arduino UNO™ (not included)

• Maximum load of 1A per output
• Maximum voltage of 30V per output
• Uses pins 8-13 as outputs, pins A0-A5 as analogue inputs and pins 2-7 as digital inputs
• Dimensions: 68 x 53mm

• Example Arduino sketch