Arduino as an APC Master Switch alternative

I was looking at getting something like to control my cisco lab at home.

Then I thought I have an arduino, all I should need is an ethernet shield & a few relays.

1) Does this sound plausible? 2) Can anyone help me with what I would actually need to buy I am a bit of a beginner at all this electronics stuff? 3) Could I trickle some of the mains power off to power the arduino rather than rely on a battery to keep it online?

My thinking is that I have one wall outlet 240v connected to each of the relays, which in turn would connect to C-14 connector which connect to the servers. I would estimate the relays would need to support 240v @ 13A for this.

Then I would use the Arduino's pins to trip the relays on and off depending on which hardware I need up.

Thanks in advance,


The idea with the Ethernet shield and the relays isn't so far off the base. You can include in your box a small power supply to power your Arduino, that shouldn't be a problem.

As to the protocols to implement, there you should if they're simple enough to be implemented on the Arduino to prevent bad surprises when the project is halfway done.


Regarding item 2) see This is a basic circuit to increase the juice from the meager 40ma/5V per pin that the Arduino can source in order to power the coil of a relay.

Selecting the proper type of contact for the relay is going to depend on your mains power. What country are you in?


I’ve ordered my ethernet module from hong kong the other day so hopefully should be here in the next week or so.

I think what I’ll do is prototype it with small relays and LEDS powered from a battery (LEDS will be the cisco gear, battery the mains).

Can you recommend a specific relay for this as well (I know what a relay is (just about) but the actual specs of each one and when they are relevent is still beyond my limited knowledge).



There's two parts to a relay: the coil, which controls the electromagnet which moves the switch, and the contacts which specify the maximum voltage and current that can be switched.

The rating for the contacts is straightforward; you stated 240V at 10A. Assuming the mains power where you are uses a hot (black), neutral (white), and ground (bare/green) arrangement then you just need a SPST or SPDT relay which will only switch the hot wire.

For the coil you want a DC coil, and for simplicity's sake it would be a good idea to match the voltage to whatever you are going to use to power the Arduino, i.e. 9 or 12V would be ideal. The coil will also have a current requirement and you'll again want to make sure your power supply can simultaneously handle powering all of the relays you'll be using.

An electronics site like Farnell, Digikey, or Mouser will have hundreds of viable relays that will fit your needs. I might suggest looking into some of the automotive styles which frequently feature spade plugs on the top of them -- that'd make mounting them in your project a lot simpler. It'd also be a good opportunity to procure the transistors and C-14 connectors that you will need.