Simple Relay Shield v2.0 kit

The Evil Mad Scientist Simple Relay Shield is an Arduino add-on that lets you use your Arduino (or shield-compatible clone, such as the Diavolino) to control a single electromechanical relay, for switching loads of up to 24 V DC or 40 V AC, at up to 5 A of current (10 A when used in normally-open mode). The relay is an "SPDT" type, meaning that it can be used either as a normally-open or normally-closed relay, so that you can choose to either switch on or switch off your load when the output signal from your Arduino is high. When operated as a normally-open relay, it is capable of handling loads up to 10 A (see note on safety below).

The relay is powered directly from the 5 V power supplied by your Arduino board, and is compatible with the vast majority of shield-compatible Arduino and Arduino-compatible boards, which operate at 5 V. (There are some 3.3 V or lower voltage Arduino boards; you probably already know if you have one of these.)

The Simple Relay Shield is sold as an easy-to-build soldering kit. It includes the circuit board, Omron model G5LE-14 DC5 relay, stacking header set, 3-position screw terminal block, the relay drive transistor, flyback and isolation Schottky diodes (to keep your Arduino safe), and an LED that indicates when the relay coil is energized. Typical power consumption is under 70 mA, when the coil is energized.

Usage:

The relay is controlled through a transistor that is typically connected to pin Digital 4 on the Arduino headers. To create a demonstration sketch for the Simple Relay Shield, open the "Blink" example sketch and change the pin number from 13 to 4.

When output Digital 4 on your Arduino is low (or if the Arduino is powered off), the "Common" (middle) pin of the screw terminal is electrically connected to the N.C. ("Normally Closed") pin of the screw terminal, and is not connected to the N.O. ("Normally Open") pin of the screw terminal. When the output Digital 4 on your Arduino goes high, the relay turns on, and the Common pin is disconnected from the N.C. pin, and is instead connected to the N.O. pin. When the relay is on, the "Coil On?" LED on the circuit board also lights up to indicate this.

This is version 2.0 of the relay shield, which now can be configured — at assembly time — to use any available digital output pin on your Arduino.

As with other electromagnetic relays, the load is mechanically switched by an electromagnet when energized. The rated switching frequency is 1800 operations per hour, under rated load.

Please refer to the relay's data sheet (PDF) for additional specifications.

The Simple Relay Shield is an open source hardware project. The electrical schematic for the kit is available for download here. Complete documentation about this kit, including assembly instructions, design files, and additional usage information is in the process of being added to the Evil Mad Scientist Wiki.

Building it:

The Simple Relay Shield is an easy-to-build soldering kit [?]. Basic electronic soldering skill is required, and you provide standard soldering tools: a soldering iron + solder and small ("flush") wire clippers. No additional knowledge of electronics is presumed or required.

The kit features easy "through-hole" construction ("No surface-mount nothin' nowhere!"), and (as it is such a simple kit) usually only takes a few minutes to build, assuming that you have soldered before. Note that you will need internet access to view the assembly instructions.

Special note on safety:

As (a) the Simple Relay Shield can handle moderate voltage and current and (b) the there are any number of Arduino and Arduino-compatible boards that the Simple Relay Shield can attach to, it is the user's responsibility to ensure that there is a safe distance between the bottom of the shield and any protruding components on the host board. If additional isolation is needed, it may be helpful to make use of an insulator shield, such as our own Googly Shield.

While the relay itself is capable of operating with AC loads as high as 120 V, we have derated the Simple Relay Shield to 40 V AC for two reasons. First, as we have just discussed, there is often very little spacing between components on the host Arduino board and pins on the bottom of a shield board. Second, the physical setup when using Arduino-type boards typically does not provide any mechanical means to prevent accidental touching of the wiring. If you choose to exceed our rating (at your own risk), be certain that you have thoroughly addressed these two points and to take any additional measures as necessary to ensure that the shield can be operated safely.

The relay shield is primarily labeled with a current rating of 5 A. However, as per the relay's datasheet, it can be safely operated as high as 10 A (AC or DC) if configured strictly as an N.O. (normally open) relay, with nothing connected to the N.C. terminal.