For dorkbotpdx last night, I made this little toy:

It’s an 8×8 red+green LED Matrix, driven by three shift registers driven by a Bare Bones Board Freeduino by Modern Device Company.

Before the meeting I just had it flashing fun patterns based on odd bit-math equations. During the meeting, I was urged to add some code to make it controllable by the Wii Nunchuk. So, I wrote a simple program that takes the X and Y of accelerometer and plots it on the matrix.

I drove the LED Matrix with three shift registers: One 74HC595 8-bit register gave power to the rows of the display, and one Maxim-IC MAX6969 sank current for the columns to the display. To turn on row 1, column one, you shift “B10000000″ into the row register, and “B10000000″ into the column register:

  1 0 0 0 0 0 0 0  
1 x o o o o o o o
0 o o o o o o o o
0 o o o o o o o o 
0 o o o o o o o o 
0 o o o o o o o o 
0 o o o o o o o o 
0 o o o o o o o o 
0 o o o o o o o o 

Altogether, it was about 30 lines of code to drive the matrix with some fun patterns.

I just received this set of prototyping boards from ucHobby and their sponsor Wright Hobbies!! Hooray!

I’m psyched. I have some projects I want to do that these boards will be perfect for.

In order to encourage us to play with electronics more, JWA and I have begun doing monthly challenges. For our inaugural challenge, we decided upon an LED Birthday Candle. This is my entry to that challenge.

You blow the center pole towards one side, and the LED shuts off. To turn it back on again, blow it the other direction. It’s a circuit known as a bistable multivibrator, or “flip-flop”.

I do like that it’s so simple and cheap, though.

My parts list is simply:

2 – 10k ohm resistors
1 – 1k ohm resistor
1 – 220 ohm resistor
2 – 2n3904 NPN Transistors
1 – LED
3 – AAA batteries (this thing’ll last forever!)

Not including the batteries, this thing costs less than 15 cents in parts. If I could work out the “blow” mechanism a little better, I think this would be a marketable product.

Okay, now for some photos:

On the breadboard:

Before being shoved in the pill bottle:

I had originally wanted to be able to shove this thing into a fat straw, like you get with a bubble tea, so I made it as small as possible, and soldered the pieces together straight rather than using protoboard:

Next: Brighter LEDs!

I’ve recently become enraptured with a little microcontroller development board called the Arduino (pronounced “Arr-dwee-no”).

This little thing is a great way to get started with electronics. You hook some electronic component to it, write a little bit of C, upload it to the board, and “tada!”, you’ve invented some new Gizmo.