videos and diagrams

Personal Pollution Protection in China and Everywhere

For USD $3.49 + tax I got a 3M 8211 flap valve respirator similar to this one at but when I'm exerting myself it's an effort to suck enough air through the small face mask. I also want to show I'm not contagious, I'm blocking bad air, especially the awful toxic PM 2.5 blowing in on the north wind every winter from coal fired power plants.

For RMB ¥75 + shipping SmartAIR sent me this 296 mm² HEPA filter at and I got a pre-filter and carbon filter in case of excessive dust or toxic fumes, e.g., aldehydes from cheap paint & carpet glue.

Seal the HEPA filter inside the box, orienting the accordion folds vertically.

Cut a horizontal slit near the top of the box, narrower than the hose diameter and just wide enough to expose all the accordion folds. Take care not to cut the HEPA filter.

Flange the hose ends and attach to the face mask cheeks.

Slit and spread the hose middle and attach to the HEPA box slit.

Make durable and air tight with duct tape and staples.

Wear the HEPA box as a backpack or even in or over your backpack. Perhaps rain-proof it with a plastic bag and cut air inlets in back.

The face mask left and right air inlets are in the cheeks and the outlet is the original flap valve. Keep the HEPA box inlet safe from rain, mud and dust.

I like the Sci-Fi look — may we all purify our precious air supply!

One Thursday evening in Dim Sum Labs, Hong Kong

ϕ1: electromagnet Electricity flows through a coil of enamel-insulated copper magnet wire coiled around a nail hammered into a block of wood, attracting a sheet metal electrode cut with tin snips.  Sparks fly as the twelve volt battery is connected across the coil, bending the electrode to noisily whack the head of the nail. ϕ2: oscillator Relay connected as an oscillater, clattering and sparking.  Similar designs clock digital logic circuits.

Relays and coils present an inductive load whose massive kickback voltage will fry the semiconductors in your power supply so please use batteries instead!

The relay above operates as a NOT gate, wired to oscillate by connecting the output to the input, chasing its own tail. Old computers, telephone switches, elevator controllers and the like are made of relays arranged in series, parallel and feedback circuits. Whether made of transistors, vacuum tubes, relays, gears, billiard balls bouncing off each other or dominoes falling, they're all variations on the same basic theme, simple elements combined in complex ways.

Wood, nails, magnet wire (copper insulated with varnish) and sheet metal worked with saw, hammer, file and tin snips are all we need to make sparking clanking logic gates, memory registers, adders, multipliers, Bitcoin miners, ... um, ok, we'd need an airplane hangar for those last two.

Theory & design principles:

One morning in ShenZhen, China

Black Beauty Watermelon in season