Day: December 23, 2016

Disassembly Required

December 23, 2016 by 29 Comments

If you really want to hack software, you are going to face a time when you have to take apart someone’s machine code. If you aren’t very organized, it might even be your own — source code does get lost. If you want to impress everyone, you’ll just read through the hex code (well, the really tough old birds will read it in binary). That was hard to do even when CPUs only had a handful of instructions.

A more practical approach is to use a tool called a disassembler. This is nothing more than a program that converts numeric machine code into symbolic instructions. The devil, of course, is in the details. Real programs are messy. The disassembler can’t always figure out the difference between code and data, for example. The transition points between data and code can also be tricky.

When Not to Use

If you are coding your own program in assembly,  a disassembler isn’t usually necessary. The disassembly can’t recover things like variable names, some function names, and — of course — comments. If you use a high-level language and you want to check your compiler output, you can easily have the compiler provide assembly language output (see below).

The real value of a disassembler is when you don’t have the source code. But it isn’t easy, especially for anything nontrivial. Be prepared to do a lot of detective work in most cases.

Continue reading “Disassembly Required” →

Cat Vs. Human Escalates With Armor-Plated Feeder

December 23, 2016 by 16 Comments

Wars generally increase innovation as the opposing sides try to kill each other in ever more efficient ways. Even the soft war waged daily between felines and their human servants results in innovation, to wit we offer this armor-plated automated cat feeder.

The conflict between [Sprocket H.G. Shopcat] and her human [Quinn Dunki] began with a thoughtfully provided automatic food dispenser. Like human vending machine customers who witness a just-purchased bag of Cheesy Poofs dangling on the end of the dispense auger, [Sprocket] learned that the feeder would dispense a few fishy nuggets when nudged. [Quinn] embarked on an iterative design process to control [Sprocket]’s off-schedule snacking. Fastening the feeder firmly to the floor, and adding obstructions to prevent her from pawing up the dispense chute — nothing seemed to stop the clever feline’s raids. [Quinn] then pulled out all the stops and whipped up a [Sprocket]-safe enclosure for the feeder from 1/8″ plate steel and copper. This seems to have put the cat back on the straight and narrow, and it doesn’t look half bad either.

All kidding aside, [Quinn]’s approach to this problem is pretty instructive. Careful observations informed several cycles of reasonable modifications until it became clear that only the most extreme solution would work. There’ve been tons of cat feeders here before, from the simple to the complex, but we think all would fall prey to the clever [Sprocket] without a little up-armoring.

Continue reading “Cat Vs. Human Escalates With Armor-Plated Feeder” →

Halogen Lamp Abused For Desoldering

December 23, 2016 by 36 Comments

[Moony] thought that it was unconscionable that IR soldering stations sell for a few hundred Euros. After all, they’re nothing more than a glorified halogen lightbulb with a fancy IR-pass filter on them. Professional versions use 100 W 12 V DC bulbs, though, and that’s a lot of current. [Moony] tried with a plain-old 100 W halogen lightbulb. Perhaps unsurprisingly, it worked just fine. Holding the reflector-backed halogen spotlight bulb close to circuit boards allows one to pull BGAs and other ornery chips off after a few minutes. Voila.

[Moony] reasons that the IR filter is a waste anyway, since the luminous efficiency of halogen lights is so low: around 3.5%. And that means 96.5% heat! But there’s still a lot of light streaming out into a very small area, so if you’re going to look at the board as you de-solder, you’re really going to need a pair of welding goggles. Without, you’ll have a very hard time seeing your work at best, and might actually do long-term damage to your retinas.

So the next time you’re feeling jealous of those rework factory workers with their fancy IR soldering stations, head on down to the hardware store, pick up a gooseneck lamp, a 100 W halogen spotlight, and some welding goggles. And maybe a fire brick. You really don’t want your desk going up in flames.

We love make-do hacks, but we love doing it right, too. Just watch [Bil Herd] extol the virtues of a real IR desoldering station. And then giggle as you do the same thing with a few-dollar halogen bulb.

Continue reading “Halogen Lamp Abused For Desoldering” →