Category: electronics

Stepper motor
Originally uploaded by bluesterror

For a future project, I pulled a stepper motor from an old 3.5″ disk drive and hooked it up to my Arduino. Turns out it’s quite easy to control these things: just periodically write bit patterns 1010, 0110, 0101, and 1001 to the 4 control wires and you’ve got a spinning motor.

I also baked six loaves of bread this weekend thanks to a cooking class on Saturday. I’m drowning in potential croutons.

Arduino POV
Originally uploaded by bluesterror

Since everyone else is doing it, I decided to hack together my own persistence of vision thing this evening. This is a circuit where you have a single vertical line of LEDs, but if you turn the LEDs on and off fast enough and wave them around, your eyes are fooled into seeing complete letters. It only took about 20 minutes to write the C code to load up onto my trusty ATmega8, then I used a camera with a long shutter period to take the picture to the right.

I realize my blog has devolved into Bob’s Dumb Project Of The Week lately. I’ll have to work on that. Lots of travel is coming my way soon: Toronto this next weekend, Atlanta in three weeks, and Warrenton, VA somewhere in between. I shall report on them soon enough.

Arduino Clock
Originally uploaded by bluesterror.

I spent part of yesterday and today assembling this monster of a digital clock. The brains behind it, like my previous project, is a Dallas RTC chip; the rest is just microcontroller glue to read the time over the bus and write the hours and minutes to a quartet of seven segment decoders. The arduino microcontroller board can run off of a 9V battery so this assembly is portable, like the, er, $0.50 worth of electronics that are in your wristwatch.

Angeline had a good question for which I didn’t have an entirely satisfactory answer: “Why?”

Clock, side view
Originally uploaded by bluesterror.

I constructed this a week or two ago, but only just now got a chance to photograph it with a real camera. This represents the first theoretically useful circuit I built with the Arduino platform. It utilizes the 7 segment decoding program along with a real time clock (RTC), blinking out the time one digit at a time. The RTC speaks a serial protocol called I2C so only two pins on the microcontroller are needed to read the time.

This is part of a project I’ll be building on soon, but it’s mostly still in the proof-of-concept phase.

Since I’ve been mucking with electronics again recently, I spent some xmas money on a Weller temperature-controlled soldering iron, my POS Radio Shack Board Burner 2000 no longer cutting it. Then I took the time last weekend to set up a workbench of sorts with some component drawers and all that good stuff. All it needs is a logic analyzer, oscope, and bench supply (yeah right!).

Yesterday I received a kit in the mail from Spark Fun for an Arduino ‘shield.’ This is a little board that plugs on top of the Arduino microcontroller board, in this case giving you a little prototyping area. You get the PCB and a few resistors, LEDs and jumper headers to solder onto the board. It took me about an hour with my new setup to put the thing together, and I must say the Weller is *great*. Every single one of my solder connections was perfect whereas with my old iron there would be huge blobs everywhere, scorch marks on the PCB, cold joints aplenty. In another 10 minutes, I had wired up a circuit that basically implements a BCD to 7 segment converter with the microcontroller (i.e., it counts from 0-9 continuously). Here are some ugly phone-cam pics. Aren’t you so cuuute wit your widdle breadboard!

Arduino
Originally uploaded by bluesterror.

I’ve had a few parts setting around a while for an upcoming electronics project, but it hasn’t gotten far off the ground because I was too lazy to spec out the control circuitry. I wanted it to be microcontroller based, but realizing that serial and parallel ports are ever-dwindling, I also wanted to make sure that I purchased/built a programmer that would still work in a few years’ time. Enter the Arduino, a perfect little development board based around the Atmel ATmega8; at only $30 for the board and chip, it’s a great deal. The chip comes pre-programmed with a bootloader that you can use over USB to upload your programs.

Programming the microcontroller is a snap. The Linux toolchain features a port of gcc and a small libc. There’s also watered down dialect of C and an IDE that noobs can use, but I just skipped to building with the arduino libraries and avr-gcc directly. Within 15 minutes of installing the necessary packages, I had my first program uploaded and blinking an LED. Pictured above is the second try, a simple RGB pixel consisting of 3 LEDs which fade among themselves (the effect is less than perfect without a good diffuser and smaller LEDs).

Here’s the code for the fade:

#include <WProgram.h>

int rpin = 9;
int gpin = 10;
int bpin = 11;

static int cols[3], i;

void setup()
{
pinMode(rpin, OUTPUT);
pinMode(gpin, OUTPUT);
pinMode(bpin, OUTPUT);
cols[0] = 255;
cols[1] = 0;
cols[2] = 0;
}

void next_color()
{
int before = i-1;

if (before < 0)
before = 2;

if (cols[i] < 255)
cols[i]++;
else if (cols[before] > 0)
cols[before]--;
else
i = (i+1) % 3;
}

void loop()
{
next_color();
analogWrite(rpin, cols[0]);
analogWrite(gpin, cols[1]);
analogWrite(bpin, cols[2]);
delay(10);
}

Don’t panic
Originally uploaded by bluesterror.

Ever since buying my Accord a couple of years ago, I’ve been an enthusiastic frequent user of the keyless entry, as well as an unenthusiastic occasional user of its far-too-easily-activated panic mode. Whenever I sit on my keys, press on the pocket where my key fob resides, or hold it just so (usually when I’m carrying in groceries at 11pm on my quiet residential street), my car’s horn starts blaring, lights flash, and I have to run to my car hitting the unlock button until it shuts up. Yesterday, I triggered it twice, so I finally decided to do something about it. So I did some surgery: I took a box knife to the traces on its PCB and after thirty minutes (made longer because I screwed up and had to fix a mistake) I now have a fully un-functioning panic button on this thing.

I hope I never need it.

CVS camera
Originally uploaded by bluesterror.

Everyone’s done it by now so it’s not cool anymore, but I now have my very own hacked CVS digital camera. For those living under a rock, CVS sells one-time-use digital cameras for $20, and video cameras for $30. The idea is you are supposed to return the camera, pay them to develop it, and they keep the camera. The only advantages of the still camera over a disposable film camera are that you can preview and delete photos after you take them and presumably you get a digital copy of the prints. So, the only thing to do is hack the cam so you can get the pictures off yourself and keep it for good.

Of course, it didn’t take long for every hacker with a logic analyzer to reverse engineer these things, so I didn’t have to do any trailblazing for the hack. I just built a cable using a USB cable (from an old digicam) and my old Palm III cradle. Then I loaded a patched firmware, a rather involved process that requires opening the camera and shorting a couple of pins on its PCB as it boots up.

Does it take good pictures? It is decent, but nothing to write home about. It has just over a megapixel CCD and a really bright flash. It is focused like your usual point & shoot, so anything closer than a couple of feet will be blurry. Still, it may make a worthy camera for some aerial photography experiments later on, and a good camera to carry places where the normal digicam might get broken or stolen. Here’s a picture of the cable taken with the camera.

(This entry tests the flickr “Blog This” button. If you read this, it worked.)