Just in time for our trip to Maker Faire I managed to get the second Mazzini prototype up and running. It improves upon the original prototype in a number of ways, but the most interesting is the addition of a triac, which means that the Arduino board can now control the power to the device being monitored.
This is where things start to get really interesting.
Now, as well as reporting the power usage to the Internet, it will also be possible to receive commands to remotely control whether the attached device is on or off. It also means we can build things such as the Light Load Lamp.
The lamp itself is just an off-the-shelf lava lamp, but it's controlled based on the state of the UK national electricity grid.
Here in the UK, the mains electricity runs at 50Hz. However, when the grid is under load - i.e. demand for electricity is outstripping the power stations supply - then the frequency drops ever so slightly. Similarly when there is too much supply the frequency will run slightly fast. You can read all about the details at the excellent Dynamic Demand website.
The second Mazzini prototype is monitoring the frequency of the mains, and reporting it along with the power usage up to Pachube. You can see the past 24 hours data below:
And when the frequency drops below 50Hz then it turns the lamp off, to show that there's a spike in demand. When the national grid recovers then the lamp is turned back on. You can see how much the lamp has been on or off during the past day in the following graph:
How is that useful?
To be honest, it's not too useful when it's just a lamp that's being controlled - it's just a demonstration of one of the applications of the Mazzini technology. However, it might be more useful if it was controlling something like a fridge. It wouldn't really matter if your fridge turned itself off when everyone goes to make a cup of tea during the ad-break in Coronation Street, but it would help smooth out the electricity demand curve, and that would mean that we'd need fewer power stations sat idling ready to cope with the extra demand.