Soldering is easy. It realy is. If you are still in doubt, head over to mightyohm.com, where you can find a really nice comic on how to solder, done by my good friends Jeff Keyzer and Mitch Altman.

Best of all, it’s totally open source!

Links

• Soldering is easy as PDF

Do you remember, when you first started your X and stared at Xeyes? Aaaah, those were the days.

I wanted to have Xeyes in Processing to have it as an example of some lines of code that could be easily integrated into an interactive demo or the like. So I thought, ok, that’s quite easy, just draw a bunch or ellipses and circles. Turns out that it is not that easy.

First you draw an eye, then a straight line from the middle of the eye to the current position of the mouse. Then draw a tiny circle at the intersection of the line with the ellipse. But how to find that intersection?

The solution is to equate the formula of the straight line with the formula of the ellipse.

  y = mx + c  // straight line
  x2/a2 + y2/b2 = 1 // ellipse

Now insert one formula into the other, and solve it for x and y. If you still know how to do that, great! I failed in a few attempts. And felt lazy. Wolfram Alpha to the rescue!

Using the Wolfram Alpha it was easy to get the right solution. See here and here for examples. Now just calculate the values for the intersection coordinates and handle some special cases (e.g. prevent division by zero).

Another example how to use math to solve real world problems

Updated 26.02.2011 to the much easier version as proposed by cjameshuff.

/**
 * xeyes in Processing
 */

int eyeDist = 60;
int eyeWidth = 70;
int eyeHeight = 100;

void setup() {
  size(450, 450);
  smooth();
  background(120, 120, 120);
}

void draw() {
  int eyeX = width / 2 - eyeDist;
  int eyeY = height / 2;
  translate(eyeX, eyeY);
  drawEye(eyeWidth, eyeHeight, mouseX - eyeX, mouseY - eyeY);
  translate(2 * eyeDist, 0);
  drawEye(eyeWidth, eyeHeight, mouseX-(eyeX+2*eyeDist), mouseY - eyeY);
}

void drawEye(int eyeWidth, int eyeHeight, int mx, int my) {
 // draw the eye
 fill(220, 220, 220);
 strokeWeight(10);
 ellipse(0, 0, eyeWidth+35, eyeHeight+35);

 float x2 = mx/((float)eyeWidth/eyeHeight);
 float t = max(1, sqrt(x2*x2 + my*my)/(eyeHeight/2));
 float sx = mx/t, sy = my/t;

 // draw the pupil
 strokeWeight(1);
 fill(0);
 ellipse(sx, sy, 20, 20);
}

Links

• Xeyes
• Wolfram Alpha Ellipse Line intersection
• Processing.js

Two years ago I posted about how to build a neoprene sleeve for a Macbook. This time it’s a sleeve for a Samsung Galaxy Tab. As last time, my mom did the work, I did the documenting

We had some remains from the first project. This piece is a front part of a neoprene wetsuit. Cut out the biggest piece you can get. Then use chalk to mark the size. The size is about 15cm x 51.5cm. You may want to cut it a bigger as you think you need it.

Now cut it out.

Check, if the size still fits.

Now sew the envelope inside out. Then cut the overlapping neoprene as close to the seam as possible. Flip the envelope back to have the outside out.

Check if the tab fits. If its too loose, you can always sew another time to make it a bit tighter. Mine got a tiny bit too tight at the first try, so you have press it a bit.

To keep the tongue in place, we decided to simply cut stripes from the sleeve.

Ok, that looks great. Now just trim the tongue a bit to make it fit into the strap.

Here’s the finished sleeve.

Ready to throw it into my bag. All together the project took only one hour. And for me the result is way cooler than any sleeve you can buy.

Links

• Flickr set with hires pictures
• Neoprene Macbook sleeve

Yay, here is my second article, this time published in the famous Elektor magazine. It’s about the synchronizing fireflies.

I met Jerry at last years HAR2009 and we chatted about the fireflies and all things electronics. He works for the Elektor magazine in the Netherlands and asked me, if I would like to publish an article about the fireflies. And here it is. Thanks Jerry, for making this possible!

Last weekend, a small group of tinkerers of Palo Altona built a MakerBot Cupcake CNC. Simone and Christian from Good School bought the MakerBot and asked Palo Altona for assistance with the assembly. Of course we were happy to help out.

We startet on Saturday and made good progress. We assembled the CNC and the extruder and made the first tests with stinking hot ABS. Yeah!

Next day was for learning firmware and tools. We switched X, Y and Z directions of the stepper motors a couple of times and managed to drive the heated nozzle into the platform at first try. *sigh*

This is the very first print out. Although it is not tight enough to drink from it, I was really impressed by the result. What a cool machine!

Here are some more pictures:

• My Flickr set
• Good School on posterous
• Christian on posterous
• Palo Altona on posterous
• Marcus Flickr set

Thanks Simone and Christian for inviting us, it was a pleasure!

This is a Pong clock for your Android phone. It tells the time by playing Pong against itself.

Sander Muller came up first with the idea to have a Pong Clock. A really great idea and a fantastic device. Then lately Lady Ada designed a wonderful hackable clock platform, called MONOCHRON. The first implementation on the platform was, of course, a Pong Clock.

As I received my new Android phone, a Motorola Milestone, I was looking for a simple project to get my hands dirty. So what could be more obvious than writing a Pong Clock.

If you want to take a look at the source, check out my PongTime repo at github. The code is not pretty as can be, mostly because of optimizations to get rid of object creation and thus garbage collection.

If you are reading this with your Android phone, you can grab the Pong Time app directly in the Android Market. Otherwise search for “Pong Time”.

• Pong Time market://search?q=pname:com.tinkerlog.android.pongtime in the Adroid Market
• PongTime repository at github
• Original Pong Clock by Sander Muller
• MONOCHRON by Adafruit

For my latest projects I used a lot of single cell lipo batteries. They are really nice. High power density, low self-discharge, no memory effect and they can deliver quite an amount of current.
But lipo battery handling is a bit more complicated as with other rechargeable batteries. You have to take care of under voltage and over charging as that may destroy the battery.

I used the Sparkfun LiPoly charger, based on MAX1555, for some time and it works really well. The only thing I missed was a way to control the current. After some research I decided to try another chip, the Microchip MCP73833.

Features of the MCP73833

Copied from the specs:

• High accuracy preset output voltage regulation
• Regulated output voltage options
• User-programmable charge current up to 1A
• Two open-drain Status outputs
• Preconditioning and end-of-charge ratio options
• Under-voltage lockout
• Power Good output

What I like is the ability to adjust the charging current and the status outputs, which should get really useful if integrated into a greater application.

The schematic

The schematic is mostly a copy of the reference design. It has three LEDs, one for power good, one for charging and one for charging complete. All pins of the chip itself are also available on two header rows. The idea was to enable easy integration on a breadboard. Actually I misplaced the rows, so they don’t fit (#fail).

The resistor R4 is used to control the charge current. I used a socket for that, so I am able to adapt the current for different batteries. The 10k resistor results in a charge current of 100 mA.

The result

All components were 0805 SMD parts, despite the MCP73833, which is 10-MSOP. This was my first attempt to do something useful with SMD. I used my brand new hot air reflow station, which turns out to work as expected. Only I had to be very precise at dosing the solder paste. Applying too much had to be removed with solder wick later on.

Issues

The next version should include a jack for a wall adapter. The two header pins are not really useful to connect to a power supply. And of course the two rows of header pins should be aligned correctly to fit on a breadboard.

As a sidenote: as you see, the board has a mini-USB connector to be able to connect the charger to a notebook.
I stronly recommend to use some kind of USB hub to test any newly build USB hardware.
I didn’t. And now I have a burned first prototype of my charger and only one USB port left on my MacBook. Although the OS warned me with “something is sucking too much, port gets shut down”, it wasn’t fast enough. So, you have been warned.

Links

• Microchip MCP73833

While we were at cheating, here is a new sticker for your notebook. It helps you to read and learn resistor values.

The first 10 direct messages to me will get one for free. And of course every next order at the Tinker Store will include one of these.

The last couple of weeks I have been busy to put up a store for my kits and now I am glad to announce the one and only Tinker Store. The very first two kits are the Programmable LED and the Synchronizing Firefly. Along with the kits I did very detailed step-by-step instructions on how to assemble and solder them. Check them out on the HowTo page.

If you encounter any problems with the shop, then just drop me an email and I will fix it as soon as possible.

I saw the funny command line interface to speech at Nerdlogger. Try this to play some tunes:


say -v Cellos "Dum dum dum dum dum dum dum he he he ho ho ho fa lah lah lah lah lah lah fa lah full hoo hoo hoo"


If you are brave enough, copy’n'paste the snippet below, replace USER and PASSWORD with your twitter account and it will read out loud the latest tweets of your friends.


curl -s -u user:password http://twitter.com/statuses/friends_timeline.xml | grep "<text>\|<screen_name>" | sed -e 's/&#228;/ä/' -e 's/&#246;/ö/' -e 's/&#252;/ü/' -e 's/<text>\(.*\)<\/text>/\1 from /' -e 's/<screen_name>\(.*\)<\/screen_name>/\1. . . . /' | say


Still a one liner