Looking Mains Voltage In The Eye And Surviving

It is often a surprise to see how other people react to mains electricity when they encounter it in a piece of equipment. As engineers who have dealt with it both personally and professionally for many years it is easy to forget that not everyone has had that experience. On one hand we wince at those who dive in with no fear of the consequences, on the other we are constantly surprised at the number of people who treat any item with more than a few volts in it as though it was contaminated with radioactive anthrax and are scared to even think about opening it up.

We recently had a chat among the Hackaday writers about how we could approach this subject. The easy way out is to be all Elf-and-Safety and join the radioactive anthrax crowd. But the conclusion we came to was that this site is a resource for hackers and makers. Some of you are going to lift the lid on boxes containing significant voltages no matter what, so we thought we’d help you do it safely rather than just listen for the distant screams.

So here follows the first in a series on how to approach electronic devices containing high voltages, and live to tell the tale. By “high voltages” we mean anything up to mains voltages, and those directly derived from them such as the few hundred volts rectified DC you’ll find in a switch-mode PSU. For multi-kilovolt EHT you’ll have to wait for another article, because that is an entire subject in itself. We’ll mention these higher voltages in passing, but their detail is best left for a Hackaday colleague with more pertinent experience.

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Overthinking Solenoid Control

No circuit is so trivial that it’s not worth thinking hard about. [Charles Wilkinson] wanted to drive a solenoid air valve that will stay open for long periods of time. This means reducing the holding current to prevent wasting so much power. He stumbled on this article that covers one approach in a ridiculous amount of depth.

[Charles] made two videos about it, one where he debugs the circuit and learns things live on camera, and another where he sums it all up. We’ll be walking you through the long one, but feel free to skip around.

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Dirt Cheap Dirty Decapping

Those tiny black rectangles of epoxy aren’t black boxes anymore. Decapsulating ICs is becoming somewhat common, and if you’re reverse engineering a chip-on-board epoxy blob, or just figuring out if the chip you bought is the chip you wanted, you’ll need to drop some acid. Usually this means finding someone with the knowhow to decap a chip, or having enough confidence in yourself to mess around with fuming nitric acid. Now Dangerous Prototypes has a better solution – Dirty Decapsulation. Send your chip to Dangerous Prototypes, and they’ll melt away the epoxy and take a few pictures of the die hidden inside your chip.

dirty-decappingDirty Decapsulation is Dangerous Prototype’s addition to their array of hacker services including cheap, crappy PCBs and SLA printing service. Dirty Decapsulation follows in the tradition of these other services; it’s not the best you can possibly get, but you’re not paying thousands of dollars for the job.

Right now, Dirty Decapsulation will take a chip, strip off the epoxy, and take a few pictures. These pictures are stitched together, producing a medium quality image of the die. No, you can’t see individual gates, and you can’t see different layers of metal and silicon. If you want that, you’ll need some nitric or a few thousand dollars. Dirty Decapsulation is just to verify the chip’s identity and give a rough idea of the layout of the die.