The battery capacity will be better with lower drain currents. To determine the battery life, divide the capacity by the actual load current to get the hours of life. A circuit that draws 10 ma powered by a 9 volt rectangular battery will operate about 50 hours: 500 mAh /10 mA = 50 hours The cell voltage of alkaline cells steadily drops with usage from 1.54 volts to about 1 volt when discharged. The voltage is near 1.25 volts at the 50% discharge point.
Sometimes building an enthusiastâs PC is more difficult than building a budget one because you have budget, but donât want to go overboard or make decisions that waste money. We hope this sub $1200 build walks the line between spending good money on components that matter without spending too much on the ones that donât.
But we're about to introduce you to one of the most exciting projects that's emerged to help redress the balance: the Raspberry Pi, a tiny, $25 computer, which runs Linux and is going to change the world (well, at least British computer education!).