Archive for December, 2017

Thursday, December 28th, 2017

About the iPhone slowdown issue

When their hand was forced by hard evidence, Apple admitted what many people had suspected: they deliberately slow down older phones, in as little as a year.

Their apology letter is a masterpiece of copywriting. But let’s have a closer look, shall we?

A chemically aged battery also becomes less capable of delivering peak energy loads, especially in a low state of charge, which may result in a device unexpectedly shutting itself down in some situations.

It’s true that batteries lose capacity over time and use. But it doesn’t so easily follow unexpected shutdowns are the result of this fact of physics. In particular, competing phones seem to avoid this problem.

They glibly follow this two paragraphs later with:

It should go without saying that we think sudden, unexpected shutdowns are unacceptable.

Cute. Apple doesn’t get off the hook so easily. Know what else goes without saying?

They have full, unrelenting, absolute control over every detailed aspect of the design of their products. They alone are responsible for the bizarre obsession with making phones thinner at the expense of everything else. They alone chose the size, composition, and performance parameters of the batteries they use by the millions. They designed the power handling circuitry, specifying its behavior under load. They alone control every scrap of power handling circuitry on the mainboard all the way down to the CPU. They alone tested their designs in as many varied circumstances as their imaginations could provide.

It goes without saying that lithium batteries are consumable components—ones they’ve deliberately made non-user-serviceable, in some cases gluing them into the inner chassis so thoroughly that they’re nearly impossible to remove. Speaking from experience here.

So in that context, no, I don’t buy the polished arguments about how this was done for my benefit. They’re definitely optimizing for something, but long-term customer experience ain’t it. -m

Monday, December 25th, 2017

Call me AJ6BD

CQ, CQ, CQ. This is AJ6BD.

I officially have a callsign. I can now legally broadcast on the amateur radio bands.

I’ve been building radios since I was ten (really). I had plenty of help from my mentor, who taught me more than I realized there was to know about electronics, AC theory, signals, modulation, ionospheric propagation, phasors, oscilloscopes, and calculus. It was with his help I built that infamous Tesla Coil for my 6th grade science project.

Despite all that, I never got into the transmit side of radio. There used to be a formidable requirement to send and receive Morse Code at a particular rate, but the FCC dropped that requirement around 2007.

Recently, I’ve experienced an uptick in interest in electronics, and a little nudge from W6RQ at work I brushed up on the materials and went in for my test. Actually three tests, which I somehow managed to pass.

So as I write this, I’m in the unusual position of having an “Amateur Extra” license, but never having had a QSO (over the air contact).

If you’re into Ham radio, leave your callsign in a comment below. Maybe you’ll be the first I make contact with. :)

73, (best regards)

Micah

AJ6BD

Sunday, December 10th, 2017

Power Supply build: part 2: component selection

In the previous posting, I went over requirements for a DIY power supply build. Now on to the fun part–shopping!

Case

I wanted something fairly compact, but still nice looking. I ended up going with Jameco ABS Heavy-Duty Instrument Case. It’s a good quality build. In metric, it’s 200mm across, and 64mm tall, which is just about right. I wasn’t looking forward to hand drilling, and worse, cutting rectangular holes in those end-plates though. We’ll come back to that.

This case has a really unusual pattern of mounting holes in the bottom surface. I’m sure there’s ready-made circuit boards that would fit that spacing, but I wasn’t planning on wiring this whole thing up at the component level. So we’ll have to stick a pin in this part too, and revisit later.

AC to DC

I originally sought to get a single board that took 120volts AC in, and came with dual, indepenent outputs. Without reading too closely, I picked up from Jameco a Mean Well “dual” output board. It looks like it was designed to provide both a DC output, as well as a battery charger output. After it arrived, a bit of inspection showed that the two outputs were not independent at all. Trying to (for example) connect them in series would create a short. So for my purposes, I had a high-quality single-ended supply only.

One down, one to go.

It would have been natural to pick up a second identical Mean Well board. But thinking about the requirements, I saw an opportunity to try out something else. The maximum current on the Mean Well was around 3 amps. Perhaps I could do better, at least on one channel? Who knows when I’ll be trying some crazy electroplating experiment and need it. So after more shopping, I settled on the GEREE AC to DC Converter 85 ~ 265v AC to DC 12V 8A Adapter/Industrial Module Switching Power Supply by way of Amazon. This baby can put out up to 8 amps.

Regulators

These things come from many different overseas manufactuers, under a variety of names, but they all look like this: 5A Constant Adjustable LED Dual Display Amp/Volt. They are actually two boards stacked togetehr with conductive risers. The bottom board is a constant current/constant voltage buck regulator, so it can produce an output anywhere from a bit less than the input, down to a few hundred millivolts. Great. Allegedly, they can handle up to 5 amps. I have my doubts, but we’ll see. (And if I blow one up, it’s easy to replace. Hooray for DIY!)

The top board is a voltage and current display. I started out with grand ideas of replacing the LED displays with larger seven-segment modules, but that quickly got complicated. At least I got a chance to learn how to lay out circuit boards in KiCAD.

Voltmeter/Ammeter

OK, spoiler alert. I ended up using separate voltmeter/ammeter modules, like these:DROK Digital Current Tester Multimeter DC 100V Volt 2A Ampere Battery Monitor Gauge 2in1 Red/Blue 2-color LED Display Car Automotive 12V 24V Built-in Shunt. So much for the larger LED display. These are only 0.28 inches, but it’ll have to do. And I like that the LEDs are different colors for voltage vs. current.

So there’s the major pieces. But there remains the significant job of hooking everything together professionally, safely, and upgradibly (if that’s a word). How things connect together is make-or-break on projects like this. Let’s spend some time going over connectors in the next installment.

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