I love headphones. It’s the only way I can listen to music much of the time; without them I wouldn’t be able to. At work I listen on Grado SR-80′s, which allow external sound to come through so I can still hear my phone ring and be aware of what’s happening around me. At home, I wear closed phones like my Ultrasone HFI-580′s so I don’t have to hear what’s happening around me, allowing me to enjoy my music and movies in peace. With all of this headphone listening, it was inevitable that I would eventually take an interest in headphone amplifiers, and I did. Recently, I built the Objective2 headphone amplifier (actually, I built two – for home and work) and in this article I’ll cover what led me to the Objective2 amp and my experience building it.
In a previous post, I wrote about how I setup a transparent bridge computer, which is able to monitor all network traffic passed through it. It works great, but to make it really useful, it needs some software that can report on the monitored network traffic in a useful manner. I decided to use ntop for this purpose, as it provides powerful reporting on bandwidth usage, which is exactly what I’m after. I’m not a regular Linux user, so I usually take the easy approach and install software through whatever GUI-based software manager is included. When I did this in Linux Mint however, I found the version available was not the latest, which is 5.0.1. I also learned that ntop has since been replaced by ntopng, which wasn’t available through the GUI. I’ve had some college courses in Linux/Unix administration, so I figured I could handle installing it “the hard way”. In this post, I’ll cover how I got ntop 5.0.1 running on my bridge computer.
I recently became interested in getting a better handle on bandwidth usage on our Internet connection at work. I wanted to see what I can do for free (or at least very cheap) so I started researching solutions using Linux. Before I can try out any software though, I need a computer that can do the monitoring. I decided to build a transparent bridge or “Machine-In-The-Middle”, which is a computer with two network interface cards (NICs) which are bridged together so that any traffic going to one card is passed through to the other. The bridge computer is installed in between two other nodes on the network, and any traffic passed through the bridged NICs can be monitored by the bridge computer. The bridge creates a slight delay, but is otherwise transparent to the nodes it is connected to.
Most of the information I used to guide me in setting this up came from Bridging Ethernet Connections at the Ubuntu community wiki and this page on how to setup a bridge in Debian from microHOWTO. I thought it might be pretty difficult, especially since I’m not a hardcore Linux guy, but I found it to be surprisingly easy. For the rest of this post, I’ll cover what I did to setup my transparent bridge computer.
Last week, I bought something I’ve wanted for quite some time: an oscilloscope. I’ve been doing more projects where a scope would be useful, such as audio amplifiers, PWM, and AC-DC rectification. And besides that, oscilloscopes are just plain cool. Of course, a scope by itself isn’t much fun, it needs something to measure. Something like an AC sine-wave, or an audio signal, or maybe… a person’s pulse rate? It’s possible, with the right sensor. Sean Michael Regan shows us how in the latest MAKE Weekend Project. I knew right away that it was perfect for trying out my scope. It was a bit of work, primarily because I modified the circuit, but the finished sensor is a lot of fun, and there is a lot of potential for doing more with it.
I built my first cMoy earlier this year, and it came out really great for my first attempt at building a headphone amp. The only problem was that it’s a poor match for the headphones I use. My headphones are all efficient low-impedance models (Grado, Ultrasone) that don’t require a lot of voltage. What they need is more current. The basic cMoy design doesn’t provide this, at least not with the OPA2132A OpAmp. I soon learned though that several DIYers have built similar “cMoy-esque” amps based on the circuit used in Grado’s RA1 headphone amplifier, which uses an NJM4556 (aka JRC4556) OpAmp, good for 70ma of current per channel. I decided to try building one, and I wanted it to be a little different. So I built it in a cigar box.
There was quite a bit of drilling and cutting involved, and I destroyed a couple boxes in the process. The volume knob is installed where the cigar maker’s medallion was previously located, which had their logo. For the circuit, I took some ideas from both the cMoy and the RA1 clones. I used some pretty high-end hardware, such as the Neutrik locking 1/4″ jack. It wasn’t because I thought it was necessary, but because it was easy to mount to the cigar box.
The result? Not very good. It’s unique, and looks interesting, but it doesn’t work very well. I ended up building two of them, and both are very noisy. Copper shielding on the second build helped, but not a lot. It might be all of the wiring needed to connect everything, or just the result of a poorly engineered DIY project based around a potentially “cranky” OpAmp, but it just isn’t a great amp. So I’ve kept the second one as a “show piece” while the first gets picked away at for spare parts. Even though it was ultimately a failed project, I’m glad I attempted it. For my next headphone amp, I’ll be using a professionally-engineered and designed circuit based around a PCB which should help ensure success.
Guns Blazing (Drums of Death Pt.1) has long been a favorite song of mine since the first time I heard it on UNKLE’s 1998 album Psyence Fiction. The song features Kool G rap on vocal duty and some amazing production by DJ Shadow. Most interesting to me though is the conversation that takes place throughout the song between the fictional spaceship UNKLE77 and Off-World Technical Surveillance (also referred to as Off-World Mission Control.) I’ve never seen the conversation included in the song’s lyrics anywhere I’ve looked, so I set out to transcribe it myself.
I’m a big fan of the Playstation video game consoles, so when I learned about the PS2X library by Bill Porter, I had to try it out. PS2X makes it easy to interface Arduino microcontrollers with Playstation 2 controllers. After wiring everything up and testing it with the sample program, I set out to find something more interesting to do with it. The result is a stepper motor that is controlled by the Sony controller. Here’s a video of it in action:
This was a random find on Ebay, just something I came across while looking for something else. I really liked the look of it, and I needed something that could measure large currents anyways, so I bought it. I have a Sparkfun digital multimeter, which is a steal at $15 and serves most of my needs as a hobbyist, but it’s best used for low current measurements, under 200ma. It can do up to 10 amps, but only for 10 seconds. It’s a useful feature, but sometimes I want to watch a circuit’s current for an extended period of time. I don’t want to buy an expensive DMM when the Sparkfun unit serves 98% of my needs, so an analog ammeter seemed like a good compromise. It may not be as accurate as a DMM, but it’s good enough for my needs.
I don’t know much about the meter, other than it was made by a company called Stansi located in Chicago, and it has three ranges of measurement: 0-1.5 amps, 0-3 amps and 0-30 amps. After receiving the meter, I tried it out, and found that the measurements it was giving all seemed to be significantly off. I was disappointed; I liked the look of it, but I didn’t buy it to be an antique, I bought it to actually use! I noticed that the connections on the underside of the meter were all corroded quite a bit, so I took all of the connections apart, cleaned all of the posts, washers, nuts and other bits and pieces with steel wool, and put everything back together. After testing it some more, it seems that all it needed was a good cleaning, the measurements are all very close now when compared to the DMM. Success!
If you’re hobbyist like me, and need to measure large currents but don’t want to spend the money on an expensive DMM that you don’t really need, then an analog ammeter may be the solution. A digital display certainly has significant advantages in terms of speed an accuracy, but if you buy a large meter, it should be easy to get a “close enough” measurement. In the photo to the left you can see the Stansi meter connected to a BigClive.com RGB controller, and it’s clear that it’s pulling approximately 320ma of current. It may not be as quick or accurate as a DMM, but there’s something about watching that needle bounce around that an LCD display can’t replicate, and for $20 and an hour of my time, it’s a good value. I expect to get lots of use out of this meter.
At some point while researching microcontroller projects, I came across several people who had used Arduinos and PICs to drive panel meters so they would display computer stats such as CPU load, memory usage, etc. It immediately struck me as something I just had to do. Here it is. My PC meter uses an Arduino microcontroller and receives the stats from a .NET Framework application I wrote in C#.Net. It’s housed in a plastic enclosure and looks quite professional IMHO. It was a fun project, and something I think most any computer/electronics geek would enjoy. I love mine, and I look forward to building more.
Here it is in action:
Read on for details on the parts and tools I used, some info on the process of building the device (and the problems I ran into) and links to download the source code and meter templates.
This past weekend marked the 14th annual Garage Sale Bonanza, held at the Saybrook Plaza in Saybrook Township, Ohio. It’s a large event, including just about everything you’d typically find at a garage sale except clothing. All of the items sold are donated to the event and it is staffed entirely by volunteers. Proceeds from the event benefit a variety of local non-profit organizations, including an animal shelter, senior center, clothes closet, transitional housing, cancer support group and several other worthy organizations. I volunteer at the event each year, organizing, testing and repairing computer equipment and misc. electronics, and every year I also shop the event. It’s a great place to find parts, tools and other bits and pieces for making things.