Cool Engineering

Info on some cool engineering projects

Saturday, June 30, 2007

Title: MacGyvering my line input

One problem I have previously noted with my laptop is the absence of a line input port. The after spending some time to Googling and consultation with a fellow engineer from work, I built and tested a small circuit consisting of only three components to convert the line-input signal into a mic-input signal. The circuit consists of to resistors which form of voltage divider providing approximately 20 DB of attenuation of the input signal. It also a includes a capacitor which the effectively removes any DC offset those introduced by the line in stage. I have already used this device when connecting out my video camera to the computer to extract some audio from a production I was putting together. The one limitation I have identified is that it only works as a mono input as contrasted that with the stereo line input provided on most computers. This however should serve well as most of my recordings of from conferences and speeches. Another recent development is my acquisition of the first two seasons of MacGyver on DVD. Soon I hope to provide a photo and circuit diagram.
This is a series of grew up with and enjoyed very much a child and am now more aware of some of the limitation of the various hacks he performs as an adult engineer. Funnily enough of the last conference I’d attended (church camp) I remembered this recording limitation of my computer a little too late, and on the spur of the moment thought to record the presentations directly onto my MP3 player – something in the best traditions of MacGyverisms.
On another note, this post was almost entirely in the multi its but spoken to using some text to speech software that I’m currently trialling. So… debate over all words completely out of place they can blame on the speech to text engine.

Monday, June 11, 2007

ROV Porthole

One feature that almost goes without saying for a ROV is a video (+ possibly still) camera. Imagine being able to hover around reef systems, or around the piers and see all the little fish swimming around. To make this possible a viewing hole must be installed which will allow the camera to have a view of the outside world.
I made the viewing hole from 4mm Perspex salvaged from an old fish tank. To get the round shape (which fits in the groove of the endcap - see pics) I embarked on the following process.
1) I covered the Perspex in contact on both sides to avoid scratching the surface
2) I scribed the design onto the Perspex using a circle I generated in MS Word and a hobby knife
3) I used a hand jigsaw (like a mini hacksaw) to approximately cut of the perplex. I had wedged the Perspex between the table and a piece of MDF - thanks to Adam for that suggestion.
4) I clamped a file into my bench press so that it made an angle with the jaws of 90 degrees. Using the jaws as a guide, I spend the next few hours shaping the Perspex to meet the lines I had scribed - regularly checking if it actually fit.

After drilling the 75mm hole in the end cap I affixed the Perspex using silicon specifically targeted at watery applications (recommended for aquariums and the like.

Sunday, June 10, 2007

UAV Wrapup

Ok, the interview of the century is now on the web:

Saturday, June 09, 2007

Stove Writeup Final

After half a dozen or so tests I have found a simple aluminium stove combination which works nicely.

- Drill three 2mm holes clustered towards the centre of one half
- Use a 0.8mm drill bit to drill the jet holes - I have been drilling about 10 in a pattern which is optimised for using a kidney cup for cooking
- Cut both cans to about 2.5cm height
- To ensure it fits together nicely put two large creases in the can that fits on top - at the top of these creases drill a small hole to prevent pressure build up

All going well I'll be testing these stoves out at Lerderderg Park in a weeks time.

PHP is your friend

Recently for a website that I manage I wanted to make a section where details of the files within a folder are dynamically displayed, showing their size along with some formatted details garnered from the file name (date, speaker and topic).
For these sort of exercises PHP is really handy and my first preference - possibly as I grew up with C and the formatting is a little similar. It has some really neat file parsing options - like fill an array with all the filenames in a directory we go:

$dir = "./Sermons/Sermon_Audio/";
$dir_handle = opendir($dir);
$i = 0;
while (false !== ($file_name = readdir($dir_handle))){
if ($file_name != ".." and $file_name != ".") {
$dir_array[$i] = $file_name;
$i = $i + 1;

To sort them just do
depending if you want to sort in reverse or not.

It has some great splitting functions to tokenise strings like to remove the file extension:
$removed_extension = explode(".", $dir_array[$i]);

And reading the filesize is dead easy (the 1024*1024 is to convert the size to MB - the function returns filesize in bytes)
$file_size = filesize($dir . $dir_array[$i])/(1024*1024);

Friday, June 08, 2007

ROV Introduction

Recently I have been busy working on an ROV (Remote Operated Vehicle), which is basically an underwater tethered robot. I had the idea around the time of the inception of our UAV project, but with little knowledge about submarines and a fair knowledge of aircraft we decided to go for the UAV. The idea has therefore been around for a while - but the motivation was somewhat lacking - until talking to my project supervisor the idea of running a ROV project for 2008 was raised. My role would be the mechanical design and supervisory for the electronics - supervising a team of final year students who would do the control and communications systems.
I figured this was more than enough motivation to start work on the ROV and so over the next little while the mechanical design steps and some ideas about how the electrics will work will be found here.
One background source I found particularly helpful was "Build Your Own Underwater Robot and Other Wet Projects by Bohm, Harry" which provided some very useful background info and some basic design and control ideas. Having adapted some of these my design is for a neutrally buoyant ROV, with two rear bilge pumps (converted to drive propellers for proportional control) and two angled bilge pumps to provide reversing, surfacing and diving motions.
The basic framework is built from 15mm PVC piping (shown in the picture).

Saturday, June 02, 2007

Fix-it 5: PCMCIA woes

One annoying drawback with my current laptop (an otherwise excellent T43 Thinkpad) is it doesn't have built in Firewire (or a sound line in for that matter with is also annoying). Since I'm doing a fair bit of video work I decided to get a PCMCIA firewire card to overcome this hurdle - so onto eBay. The $18 car that I got looked kind of cheap (they even spelt insert wrong on the card label - I'd rather not inset the card). Anyway to cut a long story short the connector on the card wasn't straight and so bent the pins within my PCMCIA socket - Grrr.
On the Lenovo site they have excellent service manuals which aided me in pulling apart the laptop and straightening things out :).
A couple of days later I purchased a card from Centrecom, though it was double the price, it was of much higher build quality and worked perfectly! Excellent.