Regular readers will remember I’d previously had a problem trying to run an Arduino from the power line of a CurrentCost CC128 energy monitor using the CurrentCost’s own PSU for both devices, wherein as soon as you connected the additional load of an Arduino, the CurrentCost stopped getting readings from its remote sensor.

The reason for wanting to do this – I should point out – is that it seems mighty stupid to require two PSUs to be able  monitor a device that is ultimately targeted at reducing your energy usage.

One of the few places I found that actually documented the CC128’s RJ45 port gave me this (abbreviated) list;

1 = +v Unregulated (Same as the PSU input – which in my case was 3.8v)
3 = +V Regulated (3.0v)
4 = GND
8 = Unit TX

I reasoned that if the CC128 didn’t want to play ball when I stole some of the power from its own PSU, maybe I could approach this from the other side and put power first to the Arduino and feed the regulated 3.3v from there out to the CC128. Having tired of messing about with a chopped-up ethernet cable, I first invested in an RJ45 breakout board and socket, so that I could whack that in the breadboard and connect/disconnect at will without fumbling around with a load of wires whilst trying to remember what colour was meant to be what.

Once done, it was then a simple case of connecting up pins 1, 4 and 8 of the CC128 interface and powering up the Arduino. For something that had so stupidly failed to work the other way round, I’m pleased to say that this worked first time.

Arduino powering the CurrentCost and receiving data back

The LCD in the above picture won’t be staying there for long – it’s simply there to show the physical link and the data in the one shot. The next step is to add an ethernet shield and do the traditional thing of uploading some data to a Pachube feed, so it can be graphed and analysed in a hundred different ways. After that, I’ll have a think about what extra data if any I want to parse from the data stream – there’s also two-hourly, daily and monthly aggregates sent at regular intervals.

The “final” stage would be to put the whole lot into a little box and tuck it out of the way somewhere with a tick in the box of my mental checklist. To do that, I’ll most likely move over to a Xino, put the RJ45 (for connecting to the CurrentCost) on the little prototype area, attach the ethernet shield and add a couple of status LEDs for things like network connectivity. Of course, having just thought that far ahead, I’ve mocked it up and I’ll also need to get some (or lots of) stackable headers to cope with the extra height of the RJ45 socket on the Xino…

Xino and ethernet shield for CurrentCost monitoring