Since one of my design goals for this synth is that it be portable, it obviously needs a to operate from a battery pack. There are a lot of good designs for lipo battery packs and charging systems out there. Also quite a few breakout boards and components from the hobbyist suppliers we all know.  But since I have no idea what the final current requirements for this system are, I wanted something pretty quick and dirty (and inexpensive) to get things rolling. And I found just the thing.

Pictured is one of those "Power Bank" battery packs that is designed to recharge your phone when you are not near your charger.  Most people probably see just that. I saw, however, a 2200mAh Lipo battery and a charge controller for $6.45 from Amazon. It would have to be reworked though. The output needs to be provided across a pair of RJ-11 connectors which is what all of my modules will be using. I guess you could hack some sort of adapter cable together to make it work, but that certainly would not be sufficiently rugged, and I wanted the battery pack to look like the rest of the modules in the set. 

Taking the unit apart was trivial. The cover snapped off easily revealing a single battery cell, and a small circuit board that held the charge controller. The board has a full sized USB socket that provides voltage out, and a mini-USB socket for charging the battery. 

I wired the two RJ-11 jacks in parallel, then wired the power leads to the back of the full sized USB connector on the controller board. 

Granted, this is a terribly simple hack. I've included it for two reasons; First, I earlier published that the first module I'd build is the power supply so I thought I should mention it. But second, and more importantly, just wanted to point out that if you're building some form of portable project that needs 5 volts, there's no need to reinvent the wheel. These cell phone battery packs come in all sorts of capacities, and are really a bargain considering what you get!PARTS USED:

• Enclosure  https://www.digikey.com/product-detail/en/hammond-manufacturing/1551KTBU/HM1146-ND/2094884
• LB1 2200mAh 5V Power Bank  https://amzn.to/2qYee80
• 6P4C Verticle RJ11 Jacks  https://amzn.to/2HX9LdS