Jeremy Rubin's Blog

Here you'll find an assorted mix of content from yours truly. I post about a lot of things, but primarily Bitcoin.

categories: Bitcoin, Shenzhen Journey.

Smell Clock

The smell clock is a device I built for the Shenzhen manufacturing bootcamp. While we were there, we had a challenge to build a prototype on a tight budget. The assignment was to build something that could denote the passage of time.

I decided, while walking around the market, that these little bottle top humidifiers were really cool:

So I knew I had to incorporate them. I walked around the market scoping out prices and couldn’t find them for a good deal. Just when I was about to give up, I found them at a price I could afford – if I recall it was a few dollars a piece, but I needed a lot.

I laser cut a case for each humidifier out of acrylic and opened up each humidifier and attached a wire to trigger the toggle switch.

In order for it to look nice, I needed some good looking bottles, so I hit the grocery store, where I found:

A bicycle built from toothpaste.

I didn’t find any nice bottles, so I ended up using some ugly ones.

The design uses 4x4 grid of individually controllable humidifiers connected to an arduino mega. Each of the bottle is filled with different fragrances.

I ended up running into trouble with the plastic case, so I cut a new one from wood.

And the finished product:

Wirebonding Factory Tour

Wirebonding is a technique you’re probably familiar with if you’ve ever taken apart a cheap toy.

It’s a slightly harder technique to employ than using a standard packaged chip, but if employed correctly can help reduce cost (raw die is cheaper), footprint, and weight. The cost per wire is really small!

Basically, rather than solder a chip down, you paste it down and then solder a small wire from the chip die to the board and then cover it in goop to protect it.

This technique used to be really hard to access, but with more automation costs have come down drastically making this an interesting technique for a cost-concious engineer.

The factory boss here was a very friendly lady, and she gave us an awesome tour!

Example of a finished wire bonded board.

A worker, by hand, places the tiny raw dies onto the circuit boards using little wooden chopsticks.

The dies are really tiny to be working with by hand!

An employee configures the machine. In the upper left, you can see a wiring diagram, as well as a computer showing the current alignment.

The wirebonding machine drops small conductive wires from the bond points.

Go! Go! Go!

After wire bonding:

Ok… maybe this is before, I can’t recall. The wires are hard to see…

If there is a mistake, a worker uses a machine to correct it. The machine has knobs which scale each human movement down by a factor of 10. This allows them to do the detailed work needed to operate on these tiny wires.

Afterwards, the boards have protective goop placed on them.

Goop laying machine.

The boards then go into an oven to cure the goop to a hard shell.

They can also do clear goops!

Manual Board Population/SMT Factory Tour

When you make a lot of a board, you get a fully automated SMT line. But what about when you only make 5? Programming a SMT line takes time and is expensive. So you can do the dumb thing – do them by hand!

Yes, even though the components are tiny the employees are highly skilled with surgically precise hands.

When you’re getting hand done SMT, it’s obviously at a smaller scale, so things are a bit more laid back you could say.

E.g., there was a random cat hanging out.

First, schematics and PCBs come in and are marked up to help the workers place parts.

Silk screens get made to put the solder paste down.

Parts get carefully placed onto the boards.

The workers have really steady hands :)

Lastly, as with any SMT process, the boards get sent to the oven.

South China Material City Tour

With my back still in significant pain from the previous nights massages, it was time for the South China Material City.

The South China Material City is an industrial region situated in Shenzhen where you can go to get raw goods or materials in bulk quantity.

It’s basically a big outdoor mall where you can go into one of many vendors and find anything you need, from gears to leather. Everyone is very hospitable and there were offers of tea at some of the shops.

There was also some (very large) indoor malls, with lots of outlet priced goods:

There was also some more random stuff, like people drying spices on their shop fronts:

Or a seemingly abandoned amusement park:

You really could find anything there, from chemical supplies: