One of the first things I need to take care of is dealing with power. I debated back and forth on whether to use AA batteries, a battery pack, a charger, or a combination of all of the above. As this is v1 of my prototyping, I decided to go with the simplest route: AA batteries.
For the prototype, I’ll be using a Raspberry Pi Zero. This device requires 5V to run (I think it can actually run on as little as 3.3V). So, we need to somehow get my two 1.2V 1900mAh Eneloop rechargeable batteries to provide 5V. To do this, I need to create a DC-DC step-up converter (e.g. a boost converter).
There are lots ways to do this. However, the more efficient ways (at least to my knowledge) all use chip regulators to facilitate in the process. Lots of companies make these. One way I find this stuff is by heading over to www.digikey.com.
For our purposes, we know we want the following:
- Surface mount component
- The 8-MSOP package (basically exposes the pins for easier hand soldering)
- Maximum output voltage in the 5~5.5V range
- A step-up function regulator
That gives is basically this query: 8-MSOP, 5.5V max output, surface mount, step-up regulator. As you can see, there are basically two manufacturers that supply what I need (there are probably many others at different supplier sites).
At this point, I actually just when to the two websites and looked at the different chip offerings. There is a Microchip version that is gives me the constant 5V that I need. Why Microchip over ST? Well, I simply liked their docs and website better. ¯\_(ツ)_/¯
So, I went with the Microchip MCP1642B-50 chip.
If you look at their datasheets, they provide a lot of great information, including some very typical usage schematics. Perfect! I loaded up KiCad EDA (I tried a bunch of different software, this was the one I settled on) and started sketching out the first schematic, which is basically just a transcription from the data sheet.
Now, please be advised. I only have the most basic understanding of how this thing works, so please keep that in mind. 🙂
The other thing I really liked about the Microchip product is that it provides a mechanism to model out the circuit to make sure things are looking kosher.