BezBlog

I'm a huge fan of DIY (in case you couldn't tell from this blog...), so naturally I love Instructables - a site with user-submitted how-to/DIY guides. There I saw a really neat "word clock" which is a clock that spells out the time in words rather than numbers, and thought it would make a cool present for my girlfriend at the time. I improvised on the design and came up with a neat glossy black finish, packaged inside an Ikea shadowbox. It turned out looking really cool: In the spirit of giving back, I wrote my first instructable so you can build your own clock just like this!

--- A demo of how the RFID door mechanism works. Normally the RFID reader is facing outward so you can wave your ID on the outside of the door to unlock it. Last semester I was lucky enough to get an order through during Sparkfun's Free Day - $100 of free electronics - awesome! Among the things I got for free was the ID-12 RFID reader , a cute little RFID module that outputs the tag ID over a 9600 baud serial line. Naturally I needed to put it to good use, so when I was bored one night (avoiding psets) I set out to make my door unlock/open via RFID. The biggest obstacle was the mechanical actuation of unlocking the door. My door doesn't have a deadbolt, which means the knob itself has the locking mechanism built in. Ideally I would have installed an electric strike , but unfortunately the cutout in the steel door frame was too small to install one. I also briefly considered sticking some sort of motor inside the door frame that would push the latch open (since the interl...

[This is my 2nd "catching up" post - I started this project in summer 2009 and am just getting around to documenting it] After finishing my 4 channel light dimmer , I wanted to create a comprehensive room automation system, inspired by fellow MIT student Zack Anderson's MIDAS project. Having just been introduced to the world of Arduino, I chose to use an Arduino as the central microcontroller. In order to make the automation more useful, I hooked the Arduino up my server (a Dell PowerEdge 2500 deskside server I picked up for free on Reuse - MIT's recycling/reuse mailing list) so that I could integrate a web interface and more sophisticated control logic. More on this later. The first step to the automation system hardware was getting all of my lights computer-controlled. I piggy-backed my 4-channel light dimmer to the Arduino's serial pins such that messages from my computer would go to both the light-controller and room-automation Arduinos. Next, I needed a...

I haven't posted anything in a while, which means I've gotten behind on documenting the projects I've been working on. So to start catching up, today's project is the 4-channel computer controlled light dimmer I built a summer ago. Basically it allows me to dim 4 incandescent lights independently simply by sending commands over a serial interface. So how does it work? Well, to actually dim lights running at 110V AC, it's not as simple as putting a resistor or two in series - this would dissipate tons of power (if you can even find a resistor big enough) and would be extremely inefficient. The trick is to essentially turn the light on and off really quickly. Then you can adjust the ratio of on-time to off-time (duty cycle) to adjust the brightness. This is basically pulse width modulation (PWM), but there's a catch - since the lights are already running at 60Hz, any old PWM frequency won't work. For example, if you tried to arbitrarily use PWM at a freq...

I'm trying something new and opening up the source to one of my projects. The source code to my wireless trackpad project is now available on Google Code - http://code.google.com/p/ipod-trackpad/. Be mindful of the license (GPL v2) and let me know if you do anything cool with the code! Feel free to submit ideas/code/patches to make it even better.

As a bit of a break from all the work around here, I decided to work on a project I've wanted to try out for a while - turning an iPod into a trackpad (like the one on most laptops) for my computer. More specifically, a wireless trackpad so I can control the computer from across the room. While looking for an existing solution, I found an app for jailbroken iPods that seems to do exactly what I was looking for, but my iPod isn't jailbroken, so that was just teasing me. So, on Friday and Saturday in about 6-10 hours, I coded up a little proof of concept. This system only relies on the Safari web browser built into the ipod touch and some custom software on the computer. Some technical details: The system uses an Apache webserver on the computer to serve the trackpad.htm file. That html page contains JavaScript that handles touches and movement on the iPod and sends that data via Ajax to the Java "backend" running on the computer. The Java backend interprets tha...