In an effort to write more, I’m going to be starting a series of posts called WILTW (What I Learned This Week). The idea came from the Engineered Truth youtube channel, which is an interesting resource for Engineering students. Some of their stuff is really interesting, and some is a lot less so. Anyway, let’s jump in…
1. It’s not hard to charge LiPo batteries
I’ve been thinking about making a DIY portable speaker with outrageous volume, battery life and sound quality. This is after a few days of camping where we had multiple portable speaker units run out of juice. While I’m still sourcing components and making high level decisions about the project, I’ve been looking into LiPo charging ICs, and there are some promising options.
The MCP7833 from Microchip and BQ24090 from TI are two very simple LiPo chargers. They seem to be able to charge any combination of cells in parallel, and they only require a couple of resistors and caps as support circuitry. I’d always thought that LiPos are difficult to charge, and they are, but it’s great to see that there are chips out there that will handle the complexity for us. Best of all, they’re really cheap! The Microchip device is just over a dollar in single quantities, and the TI is just under two bucks.
I’m going to design up a board for one or both of these as PCB design practice, and it’ll be good to have this module created and tested for use in projects later. No more paying SparkFun 8 bucks for a charger when I’ll be able to make ten of them for $40.
2. Finding BOMs for consumer electronics
The Jawbone Jambox is pretty much the benchmark for portable bluetooth speakers. I was curious how big a battery was in it (among other things), and I went googling for a teardown. Luckily, I stumbled across a full BOM analysis and teardown from Globalspec, which interestingly, is a subsidiary of Mouser. Here’s the link
Turns out that the Jambox has only an 800mAh Li Ion cell in it, though it still gets decent battery life. I’m thinking that they could’ve easily gone with a cell twice the size without affecting the cost that much. Interesting decision going with something so small, but I guess that speaks to the price these devices are designed down to. By Globalspec’s analysis, the BOM is under $30, and the box sells for $230 in Canada. Also interesting is that they’re mounting the battery behind the passive bass diaphragm. Maybe the battery is so small because they needed a certain mass on the diaphragm and it was too complicated to add another battery elsewhere.
3. Drupal is tricky
I’ve been neck deep in Drupal this week, and the learning curve is steep, at least compared to what I remember wordpress being. It’s also obviously a very powerful CMS, but I’ve been struggling to wrap my head around its backend UI. Drupal strikes me as something made by software people, without as much concern for usability. That’s fine, since it’s got some serious power, but it’s also difficult to work with as a beginner.
I’ve been annoyed at the number of sub menus that I need to access just to do one thing, and the placement of save buttons doesn’t always make sense. I often drill down, change something, then exit before hitting save because the button is placed somewhere weird. That and it keeps borking up on me, and my backend UI will make itself like 5000px wide, so I need to do mad horizontal scrolling to find anything.
Overall I’m impressed at the power, but still working to become familiar with the feature set and the development process.