Give me power
You'll remember from the previous chapter that most things to do with the GPIO operate on a +3.3V level, rather than the +5V level that is often associated with digital circuits. This is the same with our I2C-based shift registers—they need to operate on +3.3V levels as well, in order to work with the Raspberry Pi.
You'll also recall, however, that there's not much +3.3V juice available directly from the Raspberry Pi—in fact, just 50mA. This is really not enough for our interface. So, before we go any further, we're going to build our own +3.3V power supply, which is sufficient for our system.
For our power supply, we're going to use a basic 3.3V voltage regulator (type LD1117V33) that will take our slightly more plentiful +5V supply ...
Get Building a Home Security System with Raspberry Pi now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
