Get Over Your Fears

October 24, 2020 by Elliot Williams 23 Comments

Some projects are just too complex, that’s for sure. But I’d be willing to bet that some things you think are too difficult actually aren’t, and it may be that all you need to get over your personal hurdle is a good demonstration. Here come three cases in point.

I was looking at the new Raspberry Pi Compute Module last weekend. They have a whole bunch of high-speed traces: things like Gigabit Ethernet, HDMI, and those crazy-fast SDI serial camera interfaces. I have no experience in high-speed design and layout at all, and frankly it gives me the willies. But the Raspberries also shipped me an IO demo board, and concomitant KiCAD design files, with the review board. Looking at it, they were just wires — maybe pairwise length-matched and impedance controlled — but also just wires. Opening up the KiCAD board file and clicking on the traces just like I do with my own designs, I’m a lot less scared. That was a revelation for me.

In a great writeup of his experience building ten different Linux single-board-computers from scratch, Jay Carlson had a similar effect on me. I would never have considered breaking out the hotplate for some CPU-and-DRAM action, and I’ve never had to lay out a PCB with a high density BGA chip before either. I’m not quite into Dunning-Kruger territory yet; I still have a healthy respect for the layout intricacies in fanning out a tight BGA CPU into a DRAM. But Jay’s frank assessments of what is easy and what is hard make it all seem within the realm of the doable.

As Mike and I were talking on the podcast about Jay’s work, Mike came clean about his fear of BGAs. I’ve done enough reflow-plate soldering, with parts that have a lead pitch that’s a factor of two finer than the 0.8 mm pitch BGAs in question, so it doesn’t seem implausible to me. And I’m 100% sure Mike could pull it off too, but he is in need of a BGA guru. Any good hobbyist videos out there?

Being a nerdy type, I’m much more focused on the knowledge and the inspiration, but maybe the courage is equally important — at least I think I undervalue it. I don’t need to lay out HDMI lines, or build a from-scratch Linux box, but I am no longer afraid that I couldn’t, and that’s because I’ve seen detailed examples of fellow hackers who’ve done the same. I might not get it right on the first shot, but I’m not afraid to try, and I wouldn’t have said the same before looking over other folks’ shoulders. Forza e corragio!

Top Ten Reasons Not To Buy A Fake MacBook Charger. Number Eight Will Shock You.

September 8, 2016 by Brian Benchoff 92 Comments

Yesterday, Apple showed the world how courageous they are by abandoning their entire PC market. It’s not time for a eulogy quite yet, but needless to say, Apple hardware was great, and the charger was even better. It had Magsafe, and didn’t start fires. What more could you ask for?

When it comes to fake MacBook chargers, you can ask for a lot more. [Ken Shirriff] has torn apart a number of these chargers, and his investigations allowed for an obvious pun in this post. The fake ones will make sparks thanks to the cost-saving design, and shouldn’t be used by anyone.

A genuine Apple MacBook charger is a phenomenal piece of engineering, but the fake one is not. In fact, it’s almost the simplest possible AC to DC converter. The mains power comes in, it’s chopped up into pulses, and these pulses are turned into a high-current, low-voltage output in a flyback transformer. This output is converted into DC with a few diodes, filtered, and wired into a MagSafe adapter.

The genuine MacBook charger is much more complicated. Like the cheap copy, it’s a switching power supply, but has a few features that make it much better. The genuine charger does power factor correction, uses quality caps, has real isolation on the PCB, and uses a microcontroller that’s almost as powerful (and a direct architectural descendant) as the CPU in the original Macintosh. It’s this microcontroller that kept you safe that one time you decided to lick a Magsafe connector not allowing the full 20 Volts to go through until the connector has connected. Until then, the Magsafe connector only outputs 0.6 Volts. The fake charger doesn’t do this, and when you poke the connector with a paper clip, sparks fly.

This isn’t [Ken]’s first teardown of genuine and not Apple products. He’s done iPad chargers, iPhone chargers, and other small, square, white switching power supplies. The takeaway from these teardowns is that cheap chargers are a false economy, and you probably should pony up the cash for the real version.