Home Is Home: The Physical Practicalities - Smart Home Automation with Linux and Raspberry Pi - page 131

into the wall on one side and the computer on the other to determine the power it's using at any particular time. This
will vary depending on whether it's in the following states:

u Idle

u Playing optical media

u Processing media (playback, recording, and transcoding all differ)

u Being used as a desktop machine

Knowing this information can help you calculate its running cost by multiplying the wattage shown by 8.76 (the
number of hours in a year, divided by 1,000) to produce the number of kilowatt-hours. This is then multiplied by the cost
per kilowatt-hour, which is generally shown on your electricity bill, to produce its TCO.

N You can even tweet your home's power usage with the simple hack known as Tweet-a-Watt, from
www.ladyada.net/make/tweetawatt . There are also alternate solutions such as Owl, AlertMe, Wattson, and Enistic.

Note

Unless the server manufacturer gives you its full power consumption data (remember that this varies according
to task), you can only make a guess at its TCO. Table 4-1 shows some approximate numbers. They have been culled
from various empirical tests, although only their relative values should be considered and only then as a guide.

Table 4-1. Approximate Power Consumption

Device Approximate Wattage Used

Desktop machine 60-250

Desktop machine (sleep) 1-5

Laptop machine 15-50

Mini-PC 6-10

Mini-ITX 5 8-20

Raspberry Pi (Model B) 1.65

Raspberry Pi (Model A) 0.715

RPi (B) with HDMI and USB drive 2.0-2.45

RPi (B) with HDMI and WiFi 2.175-2.4

CRT monitor 80

LCD monitor 35

DVD/CD-ROM (desktop) 20

DVD/CD-ROM (laptop) 5

Hard disk (desktop) 14

Hard disk (laptop) 4

USB-powered devices 2 (each)

9OUCANFINDAMORECOMPLETEPOWERCALCULATORFOR-INI)48MACHINESAT www.mini-box.com/site/mb/Power_MB.htm