So, you've now added your Bridge Rectifier and Transformer to your $3.2bln Nest Startup prototype. You just need to connect to power up your Raspberry Pi.
This next step is pretty straight-forward. To make life easy, you should buy a USB A Jack to Wire Lead connector at element14 or Newark Electronics: here. This jack will allow you to plug in a typical micro USB cable to power up your RPi.
After you purchase the USB A Jack to Wire Lead connector (above), see the spec sheet for details on how to hook it up to your Transformer: here.
Then, connect the black wire of your USB A Jack to your Transformer GROUND OUT (-) pad by soldering it together, and connect the red wire to your Transformer POWER OUT (+) pad by soldering those together. That's it!
Plug in one end of a standard micro USB cable to your USB A Jack, and the other end to your Raspberry Pi. Then connect your 24VAC power from your house thermostat wiring to your breadboard Bridge Rectifier as mentioned in Part 3/Step 4 and turn your circuit breaker back on, or use a temporary power source on your workbench as described in the later section of Part 3/Step 4 to test it.
If you reach this point and you haven't fried your Raspberry Pi, then that's a very good thing. If you accidentally see white smoke coming out of your Raspberry Pi board, shout out your favorite expletive and quickly unplug everything. But don't worry, just go back to Part 1 and buy another one. Heck, they're just $35 each! Buy, 2 or 3 more, just in case... ;-) Wouldn't hurt.
When you reach this point, and your RPi powers up correctly with very little or no swearing, do a little dance and get ready for the next step in building your own $3.2bln Nest Startup, which is where you connect up the LCD touchscreen.
Full series of steps: