Continuous condensate drainage from an off-the-shelf dehumidifier

Recently I moved to Hong Kong. Hong Kong is great! The near-constant 95% humidity levels, though, are not; I tolerate them very poorly. I bought a Hitachi RD-210EX dehumidifier, which works great, but its reservoir has about 4.5 L of effective capacity whereas the amount of moisture removed from a tiny 10 m² room in 24 hours can approach 10 L during rain. It quickly became annoying to empty the reservoir manually, more so when the full switch trips while I sleep. Clearly, some automation is needed.

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Line art photography cleanup

Often, photographs of line art, such as schematics, contain lots of noise: glare, unwanted reflections, uneven lighting, etc. In this note I present a simple and reliable cleanup method using GIMP.

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Wire reel holder

In order to store and dispense wire conveniently, I made a wire reel holder from PVC pipe. This technique is more generally applicable for prototyping cheap, mechanically weak, easily disassembled frames.

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SMD reflow with a blowtorch

I’ve designed a circuit with, among other things, an integrated buck converter (Wurth 171050601), which has an exposed pad. While the rest of SMT devices on the PCB can be easily soldered with an iron, this IC posed a problem, since the exposed pad is completely inaccessible.

I didn’t have an SMD rework station, or a hot air gun, or a hot plate, or a stove and a skillet (just moved ~8000km, come on). But I did have a blowtorch, so I decided to figure out if that can be used for reflow.

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Printing labels on Epson TM-T88IV

Epson TM-T88 is a series of thermal receipt printers that are very common and can be found on eBay for as little as $10, as well as elsewhere around the world. It is not designed to print on self-adhesive labels but, given that it has a cutter, can be easily and reversibly adapted to doing so.

In this note I demonstrate how to reliably print labels on a TM-T88IV.

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Casting silicone using modeling clay pattern

I have tried hand-forming a pattern using modeling clay, cast an RTV silicone mold around it and then destructively extract the pattern by heating it in an oven.

This does not work: silicone conducts heat poorly, and the modeling clay, generally, tends to catch fire before it liquefies.

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Cleaning an Edwards EXT250 turbomolecular pump

Recently, I’ve soaked my EXT250 turbomolecular pump in rotary vane forevacuum pump oil by not following the proper shutdown procedure. In this note I describe my attempt at repairing it.

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Ground loop in a lab power supply

Today, I decided to finally plug in my instruments properly, and plugged both my cheap lab PSU (ARKSEN 303D) and oscilloscope into sockets on the same strip with real ground prongs. After connecting the scope ground with the PSU negative rail, it quickly became clear that something’s wrong, because the wire connecting them went white-hot and sort of caught fire.

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50W LC resonant converter, power board V1

In this note I will describe a part of a 50W resonant LC converter that I am designing. The converter will be modular: it will feature a control board with an Ethernet interface, a frontend board with a rectifier/multiplier and a matching network to allow current/voltage readouts, and a power board with the high-voltage transformer, its driver and signal isolation.

This note describes the first revision of the power board.

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Measuring diode recovery time

After assembling a full-wave rectifier out of some 1A7 1kV-rated diodes, I noticed that it does not, in fact, rectify. I speculated that the diodes I used have a recovery time too high. Since it was not specified in the datasheet, I decided to measure it myself, which I describe in this note.

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