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Arduino-Compatible I/O Controller

Want to control something - anything - with commands from your PC? Perhaps turn sprinklers on and off to water your garden? Maybe read some sensors? Or even sequencing Christmas tree lights in time with music? (OK, so we're getting in early!) Making the computer output the correct information is one thing. Interfacing that data to control real-word devices is another. That's what this nifty little relay box is all about.

Design by Greg Radion#
Article by Greg Radion and Ross Tester


8 Relay outputs 5A 250VAC

4 Opto-isolated inputs 5-30VDC

3 Analog inputs (10-bit)

Connections via pluggable screw terminals

0-5V or 0-20mA analog inputs, jumper selectable

Power indicator LED

Arduino compatible

Accepts Arduino shields (Ethernet/XBee)

USB virtual COM or RS485 input

Suits Windows/Mac/Linux/etc

Easily connect multiple units far apart by RS485

All enclosed in professional-looking plastic case


Power Supply: 9-16V DC (12V Nominal) ~200mA + external 5V drain

Analog Input ANx: 0-5V: ~500kΩeffective resistance with no jumper installed

0-20mA: ~250Ωeffective resistance with jumper installed

Opto-isolated input: 0-30V, ~1kΩeffective resistance

Relay outputs: SPDT contacts rated to 5A (resistive), 250VAC / 30VDC

5V auxiliary supply: 200mA

The project, developed by Ocean Controls, is based on the hardware of the Arduino physical computing controllers. It can be programmed as a stand-alone controller using the free, open source Arduino environment.

They’ve called it the “Relayduino”, for obvious reasons.

Click for larger image

Internally, the controller is “shield compatible”, allowing the use of many extension boards designed for the Arduino Deumilanove (see the panel later in this article).

As shipped, the controller is loaded with a “sketch” (also see panel!) that receives simple commands over the USB or RS485 serial port and switches relays or responds with the status of inputs. This sketch is available on the Ocean Controls website as an example of Arduino programming for the controller.

Multiple controllers can be connected to one or more PCs in an RS485 network. Each controller can be assigned an address and will respond to commands addressed to them.

A simple ASCII protocol allows control from Windows/Mac/Linux using either USB Virtual COM drivers or RS485.

Additionally, multiple devices can be connected to one RS485 bus, allowing control of many devices from one USB port.

The relays are capable of switching up to 5A at 250VAC, 10A at 120VAC and 10A at 24VDC but the PC board tracks will only handle up to about 5A.

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