Cool Engineering

Info on some cool engineering projects

Sunday, October 07, 2007

Throat Mic Photos

As requested here are some photos of the throat mic mod:
The completed throat mic (identical to the original from the outside)Throat mic with the microphone pickup circuitry displayed:

Electret mic condenser from Dick Smith or Jaycar electronics (~$3)

Throat Mic Mods

Having experimented several years ago with different tactical setups for my 'army games' I had touched upon using throat mics (not that dissimilar to what special forces use). One problem I encountered was mounting the mic so it would stay pretty much in position as I moved, and making the earpiece robust enough so that it could survive our tactical incursions.
Skipping forward 7 years I decided to purchase a cheap throat-mic off eBay (figuring this might help out for outdoor paintball). I have Uniden CB radio's, but since I couldn't find any throat mic's for them I went with an iCom mic - which had the same connector on it - I figured it would do basically the same thing. Skipping forwards a week - the mic arrived, I plugged it in and got absolutely nothing. Sound would come out of the earpiece and when I tapped it vibrations would come though the other end, but no voice. Whipping out the meter, I found that the resistance across the mic connector on the throat mic was double that of my (aftermarket Uniden) handset. Opening up the Uniden handset revealed a very simple circuit: an electret mic condenser in parallel with a 100pF cap and a 3.3K resistor. Upon discovering this I removed the flatter mic element from the throat mic with its connected circuitry and duplicated the circuit I found in the Uniden handset. Though repeated testing I found that in a throat mic configuration that it seemed to work better without the cap and resistor - I guess because it is working on more delicate vibrations from the voice box as opposed to a direct pressure wave. The cap would likely act as a high-pass filter, while the resistor in parallel with the mic resistance would reduce the sensitivity whilst possibly shifting down the non-actuated resistance to a lower level.

Thursday, October 04, 2007

Paintballing - Melbourne indoor paintball

Although this is not strictly and engineering post, I have observed that a huge number of techies enjoy paintballing - possibly tied in with all the FPS they played as kids (and older kids). Last weekend was my 4th paintballing incursion, at my 3rd venue. It was also my first time indoor paintballing, which added quite a new dimension to the game.

The floor was carpeted and absolutely covered in paintballs and a smearing of paint. This made for some great diving action - allowing me to do huge power-slides to get behind cover. My commando like tactics came at a cost though – over all the games I was hit only a handful of times - and only have one bruise to show, but my whole body came away aching. Lessons from this: 1) stretch first, 2) I'm not Jason Bourne.

Some other interesting dynamics of indoor paintball were:

- All the barriers were blowup air filled barriers - and would move if you touched them - so you could work out were people were by seeing what moved.

- Since everyone was much closer in I couldn't use my ears as much to determine when the enemy was firing and withdraw before the paint started reaching me - I can normally do this outdoors.

- There wasn't a noticeable change in pitch when the gun was just firing air as opposed to paint. Possibly because outdoor It was lost quieter I could notice a change in pitch when you turned the gun upside-down and fired just air - indoor they sounded much more similar.