March 2013 Archives

Surveying tool

My Dad is a retired civil engineer, but still does some jobs on the side. This one involved a fairly tricky septic system install. He needed precise elevations to locate the septic field and generate a topographical map of the property.

On our first trip I just assumed I'd be holding the stick but instead I was operating the transit. Did I mention this was my first time operating a transit? We got some preliminary measurements, but I realized this piece of paper and graphing was just silly. While I'm sure you can buy an expensive surveying program to do this, we don't need this very often, and how hard could it be to write?

First was my browser-based input app. I used this on my iPad to enter the numbers and verify them.

survey1.jpgThey're plotted on a neat map but it's all done in client-side Javascript because the site had awful Internet data coverage. It's actually generating a SVG vector drawing on the fly using jquery.svg, so I can export a high quality printable graphic perfectly to scale.

That was pretty cool, but it was still necessary to interpolate the points to generate a topographical map. I figured out a suitable algorithm involving way more trigonometry that I've used since high school, but generated 3 times the number of data points in interpolation:

survey2.jpgAnd then plotted the points out on the graph:

survey3.jpgVery cool! There was also a second diversion where I server-based solution where you could upload the measured data points and get back an Excel spreadsheet. Who knew that in an hour you could be exporting fully formatted xls Excel spreadsheets with all of the columns sizes and formats not just comma separated values! That used Apache POI, a Java library for manipulating Microsoft Office documents. Cool stuff!

TV Audio

I wanted to get audio from my TV to the other side of the room, where my stereo is. Here's what I came up with.

First problem: My TV doesn't have a plain line-level audio output! It has a headphone jack and a coaxial S/PDIF output.

Funny thing is that it actually does have a line-level audio out. When I took more pictures to add to this blog post I noticed it, but I swear it wasn't there before!

Even without one it's not a huge problem. This little box does the trick. It's a S/PDIF to unbalanced audio (RCA) converter. It works with both optical and coaxial S/PDIF in, and I already had one I use on another TV using optical S/PDIF and it worked great there. The S/PDIF coaxial connection is the blue cable, above.

So now I have a regular unbalanced line-level RCA phone plug signal - how do I get it to the opposite side of the room?

All of my wiring uses the Leviton QuickPort wall jacks. Browsing the catalog of devices, I found these nifty devices: They're audio over unshielded twisted pair. The picture is from, as I forgot to take a picture before I installed it.

Basically with one 4-pair cat. 5 cable you can run a stereo audio connection. Perfect! I fished the wire, ran it through the basement, and switched the existing plates to ones with 2 more holes.


At the other end, theoretically I would have just run the audio into my mixer and be done with it. Unfortunately, I get an awful hum, and it seems to be the TV's fault - there's no hum until I make the last coaxial S/PDIF connection.

Fortunately, this little box, a Behringer hum eliminator, came to the rescue and it worked perfectly! The photo is from, which is also where I got it from. I uses unbalanced 1/4" mono TR plugs, but so does my mixer, so that worked out okay.

stereo5.jpgAnd that did it! It sounds much better than my TV's built-in speakers.

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This page is an archive of entries from March 2013 listed from newest to oldest.

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