I’ve spent a lot of time on conference calls, probably too much.  I try not to let that stop me from doing productive work while I’m on them though.  With a good headset, I can participate on a call without disturbing others and have my hands free to do whatever other computer work I have to.

Landline Headset

Typical Mono Landline Headset

One thing that annoys me about most phone headsets is that they are really nothing more than an altered phone handset that you wear on your head.  They are mono, with a single, wimpy speaker, like the one on the left.  Staying on the phone for a long duration with only one ear participating is kind of annoying.

I’d much rather have a more comfortable PC headset that I use for skype conversations.  I purchased a 3.5mm to PC Headset adapter so that I could use my PC headset with my mobile phone (most have 3.5mm jacks).  This adapter worked well, and allows PC headsets to be used with 3.5mm jacks.

3.5mm to PC Headset adapter

Since that worked well, I wanted to do the same thing for my standard telephone, which had a 2.5mm jack.

I started by looking at converting the 3.5mm plug from the adapter I used with my mobile phone to a 2.5mm plug, required by my office phone.

An adapter like this cost only a few dollars, so I ordered it.  This worked, but not quite the way I had expected.  Even though my PC headset had two headphone speakers, sound only came out of one side.  This makes sense, since traditional phones are mono devices.

What I really wanted is the sound to come out of both earphone speakers (right and left) – even if it was the same mono signal going to both sides.

I could have tried an alternate path, like purchasing a PC to 2.5mm adapter, but I suspected that this would produce the same result.  Instead, I started searching for an adapter with 2.5mm plug on one end and 3.5mm jack on the other end.  In addition, the sound on the single audio channel of the 2.5mm plug should be duplicated to both channels of the 3.5mm jack.  After much searching, I could not find such an adapter.  I did find an adapter that did this for audio only,  but did not handle the microphone signal.  I can’t believe such a thing wasn’t available for purchase, and I still think it’s my error in not phrasing the search correctly.  However, it didn’t seem that hard to just make one from parts, so that’s what I did.  I also didn’t find anyone else describing a simple DIY project to handle this, so I figured I’d do that at the same time.

So what I’m trying to build is an adapter that plugs into a 2.5mm traditional mono telephone headset jack, so it should look just like the jack on a standard one-headphone headset:

2.5mm Plug

and on the other side ends in a 3.5mm 4 conductor jack:

3.5mm jack

capable of receiving this 3.5mm 4 conductor plug:

3.5mm plug

What I essentially want to do is map the mono audio channel to both the right and left audio channel of the 3.5mm stereo plug, like this:

Desired connections between plugs.

In my case, this mapping works.  Different devices use different pinouts.  I discovered this largely through trial and error.

The 2.5mm jack I used was purchased at Mouser.   I’m sure there’s a better option for this, as this one was quite difficult for me to work with.  I didn’t find another option, so I made that work. I had to remove the outer ring to get to a decent solder point, then I used a multimeter to figure out what connects to what, as shown:

2.5mm plug, with connections

It was difficult to get the points hot enough to take the solder, but after ruining one plug, I was careful and eventually successful at the second attempt (always buy an extra if the components are cheap).

2.5mm connected

It’s not pretty, but it works.  The jack I purchased was much easier to use given my meager soldering skills.  Its connected to the plug like this:

Jack connection

After the jack’s cover gets screwed on and I put some protective heat shrink tubing on it, it looks like this, and works like a charm.

All done

Update: Eventually, the solder connections on the plug wore out. I searched for ‘2.5mm stereo male plug’ on ebay – plenty of hits and easier to work with. I purchased 20 for $5 of these:


2.5mm male plug from ebay

Connections work out like this:


2.5mm male plug, without cover

and the finished product:


All soldered and finished


Retractable wheel Desk

October 11, 2010

I needed a desk that looked solid and part of the builtins surrounding it, but that could be moved fairly easily without lifting it. To move around easily, I wanted it to have wheels, but I didn’t want them to be visible at all. I also didn’t want the desk to move once it was in position (no accidental rolling). If I installed braking casters under the desk, the whole desk would have to be elevated and the wheels would be partially visible. Furthermore, I’d have to get to the break levers on each of the wheels, which would be awkward.

I went in a different direction, inspired by an old episode of The New Yankee Workshop. In the episode, Norm creates a work table that sits solidly on legs at the same height as the table saw. Simple retractable wheels are made with door hinges and casters. I liked this so much for the workshop that I made one.

My desk would use a similar technique, only more compact and, because of that, slighly more mechanically complicated. The wheels are completely hidden when retracted.

The best way to describe this is through a series of pictures. First, to provide the overall picture, the desk currently looks like this (the drawers do not yet have fronts – I’m in the process of making raised panel fronts for them)


Hidden inside the bottom of both columns of the desk (below the bottom drawer) are the components of the retractable wheel system.


The first component are the wheels/casters. The casters are mounted on strips of plywood, with a total of two casters per strip and two strips per column. The strips are attached to the inside of the columns with hinges. Here’s one of the strips, all attached:


And here’s a view of both strips attached, looking down from the top of one of the desk’s columns.


At this point, the plywood mounted wheels flip up and down freely on the hinges.


Mounted above the wheels is a piece of plywood that forms the bottom of the storage area (the part where the drawers will be mounted) of the desk. The underside of this bottom piece has mounted a couple of strips of plywood, reinforced (and weighed down) with some angle iron. These strips are also mounted on hinges.


When in the down position, these stilts support the wheels, keeping them from retracting. When up, they allow the wheels to flip up and out of the way.


In the New Yankee Workshop table, the stilts were very long. When the table was lifted, the stilts swung down with only the power of gravity and locked the wheels down. This did not work so reliably for the desk, since the stilts are only a few inches wide. To assist the process, I installed some cord that could be pulled to lift the stilts up and pull them down. To make things work smoothly, I used some small pulleys in places where the cord changed directions.

This picture shows the first cord, which, when the middle pulley is pulled, forces the stilts into the downward position (where they will hold the wheels up).


Two separate cord setups are needed for each desk column. Pulling one of the cords pulls the stilts down, pulling the other pulls the stilts up. Here’s a video that shows this work in isolation:

Here’s a picture of the full array of pulleys and controls, installed into one of the desk’s columns.


And a short video of it in action, on its side:


Once all assembled into the desk, it’s operated in the following manner. From a rested (wheels hidden) position, you lift the desk a little bit (while sitting on a chair at the desk) with your knee and simultaenously pull the cord that moves the stilts into the down position (perpendicular to the bottom). At this point the wheels will take the load of the desk so you can wheel it around.

From the wheels down position, to get it to the rested (wheels hidden) position, once again lift the desk slightly with your knee and pull the cord that draws the stilts up (into a more parallel position with the bottom). Stop lifting with your knee and it should be resting completely on the floor with the wheels totally retracted and hidden.

This short video demonstrates the process:

For a more detailed description of the build, see this flickr set.