Alex's Mobile: the wood work has been assembled, and now needs some varnishing before I put all the electronics in. The electronics has been moved from a breadboard to full soldered vero board.

On the Contraptor front, last night I built all the linear bearings, linear rails and sliding elements and almost completed all the shaft mounts.

Tuesday's are normally London Hacker Space meetups, but tonight, I shall forgo the cheese and booze and carry on working at home.

I've back dated a load of the updates, as I'd been meaning to post blog entries about the work, but hadn't gotten round to it.

So far I have a 3d design worked out a working prototype circuit and a full breadboard circuit also designed.

I'll try and put up some full photo's soon and maybe even some video of the prototype.

So I decided this one would be different, and I would be able to upgrade it as he ages.

It will involve RGB LEDs colour cycling, driven by an Arduino (well Atmega128/328 microprocessor anyway).

It will also have two controls initially:

1. Timing control to control the speed of the colour cycling.
2. Max brightness control (self explanatory?)

The idea is that this mobile will be self contained, and capable of running from a single 9v or 4x AA batteries, or from a wall wart, and be light enough to hang safely about a cot or crib.

Update 5th Dec 2009:

Have a working Arduino circuit using 74HC595 shift registers to control the individual colours on single LEDs.

Will try and post a circuit diagram shortly.

Update 14th Dec 2009:

Here is the circuit breadboard for the current design:

Update 7th Jan 2010:

Managed to source some balsa wood and new craft knives to make a mobile spine. Want something less boring that just a straight dowel with things hanging.

Update 14th Jan 2010:

I came up with something less boring after a Yahoo! image search browsing session, and completed the 3D draft designs for Alex's Mobile and here's what I have so far.

LEDs will be positioned upwards onto the platter above to reflect light downwards, spreading the light over the different platters, in a hopefully interesting pattern.

Above is the view looking up at the mobile.

View from front, one perspective.

View from front, different perspective.

Most of these will be electronics based, but may well also pull in different disciplines.

Such as the Baby Mobile I'm making for Alex, which entails, woodwork, mold making, design and electronics.

My Contraptor kit has been shipped, and should be with me shortly.

The team had some issues with the initial run of kits, so I'm getting a Beta set, and they will ship me a corrected version, when they get the fabrication issues sorted out, at their cost. (Kudos to them, thanks guys!)

We noticed at Yahoo! that we were started to get lots of timeouts from Facebook's APIs that we use on the Yahoo! homepage.

I've not heard anything official from Facebook yet, so this next part is all speculation.

I suspect that as a user updates their privacy settings, as forced to the first time they hit facebook.com now, Facebook flags that users account is dirty (something changed) and purges the cache of the users stream data.
Now that the cache is empty for a particular user, when a friend of that user views Facebook, the backend servers must go back to the master data source and confirm permissions on what is visible before it is displayed.

That is fine when you have a few users updating their permissions, if however you force ALL your users to do this, you site rapidly becomes overwhelmed, as you effectively removed your cache. This effect is known as "The Thundering Herd".

As the load increases, due to all extra requests for data that would normally be handled by caches, you start to get race conditions as requests return and try to populate the cache. Also as the load increases, requests start to take longer as connections are kept open while backends are queried. Because connections are being kept open, the server stops handling requests, as there are no more connection slots and you start to get errors as clients can no longer connect.

How do you prevent this. Don't push changes that require you whole userbase to update their records at once. Stage the release, starting with 1% until you can guage how much load it will generate on your servers. Then you can safely ramp up your change safely.

It has been posted on to a fellow hacker in Kent.

In the end I added quite a lot of stuff to the box. Amongst other things a 6MP CCD from an old Fujitsu S20 pro camera, a bunch of motors from CD-ROM and floppy drives and a few discreet ICs

Soon I will try and post an update about what I did with the switches I took out of the box.

There is some neat stuff in the box and I'll been sending it on shortly. I have a bunch of junk to add, and here are the photos.

I've removed a board that contained a load of backlit LCD buttons, probably to be integrated into the chest of a robot of the as an  emergency stop/go kill button etc.

I happened to have an Arduino Mega and a recently purchased WaveShield in my laptop bag.

So that lunchtime I mocked up a cardboard box with the Arduino + WaveShield with a couple of buttons.

Picture to come soon.

The first version, I had no resistors in my bag, so couldn't ground the digital inputs. This actually ended up with some pretty funny results around the office, as when ever someone approached Cheesoid, he would randomly start talking.

So as an extra feature I resampled the video clip and added more phrases that play at long random intervals.

He had contacted me because he had seen my name on the TGIMBOEJ.org, a site that coordinates Migratory Boxes of Electric Junk on the Internet.

My name has been down on this site for at least a year, finally I get to participate!

So within a few days it should arrive and I'll document here what's in it and what I do with whatever I find.

I also have to add some stuff. I think for starters a NX18 Nixie Tube as seen in the Adafruit Ice Clock