I've finally written my book about the injured praying mantis that was my 'pet' for 6 months.
The Mantis story

The $4 sound activated flash trigger.

I recently decided to try and make a cheap version of the sound activated flash trigger.

I got hold of an Arduino sound switch, readily available for around $2 on Amazon.

The sound switch has 3 pins which makes it really easy to wire up. At the bottom is the voltage input wire[VCC] , allowing from 3-5 volts, then the "ground" [GND]pin in the middle and the "out" [switch] pin.

I used a 3 way battery holder which provides 4,5 volts when 3 AA batteries are fitted. I used a fairly short pc cable and would advise making it much longer for a practical sound switch so you can move the flash around easily.

It's relatively simple to wire up. Obviously your red wire from the power supply goes to "VCC" and the black ground wire goes to GND. The only tricky part is connecting the pc wires to the circuit. Plug a pc cable into your flash with the two wires bared back. Connect a volt meter to measure the trigger voltage of your flash. If your flash doesn't have a pc port you can buy a pc hotshoe adapter. 

For older flashes you can also have a look at Botzilla for a list of flash trigger voltages. If the trigger voltage is too high you will fry the circuit. Most modern flashes will work fine with it. Another option is to use it to trigger a wireless flash device so the flash is not connected directly to the circuit.

Have a look at the folowing image and take note of the colour of the leads from my meter and the colour of the wires from the pc plug connected to my SB26. I have 4,29 volts at the pc wires but my red lead is connected to the white wire and my black lead to the red wire - in this case perhaps it is the result of buying cheap pc cables because it appears that red is my ground and white is my positive feed.

So once you have established which is your positive wire from the pc plug, white in this case, solder that to the "out" [switched] pin. If you put them the wrong way around don't worry too much about it, it simply won't switch and will keep the green trigger light on on the circuit board, then you can just swap them around to get it right.

I have had this system running for two days and driven the guys at work crazy with it - so I know it will last. I had it connected to my SB26 on 1/64th power and tested the sensitivity adjustment [little grey '+' screw in the middle of the blue box] all the way down to the point where simply talking set the flash off. Turn it counter-clockwise and it gets more sensitive, to the point where it stays on. Turn it clockwise and it will get to the stage where you will need a really loud noise to make it switch.

It's really cheap and easy so what's the catch? It has no delay built in so if you were to break something for a high speed photo you run the risk of further noise triggering the flash several times during the exposure. See my blog on high speed photography for an explanation.
One work-around is to set the sensitivity very low so it needs a rather loud noise to trigger - that reduces the risk of multiple flashes during the exposure.
I have tested this using my Nikon SB26, Nikon SB800 and a Yongnuo 460 with no problems.
For only $4 worth of components what have you got to lose? :)

This is my ebook on the subject of high speed photography if anyone is interested.
Understanding Explosure
http://www.amazon.com/Understanding-Explosure-Desmond-Downs-ebook/dp/B00C5TP504

The rants of the future. Stills from videos.

The idealistic blogs about why you shouldn't hand over digital images, give away work free or undercut professionals, or "ask a photographer to work free because you wouldn't ask a plumber to work free" etc.  are all getting rather tiresome and 'stale' now. All they are doing is getting the authors sites more views [= advertising earnings] and stirring up a few passionate fans who get swept up by the emotions of the moment to share the post with others so that we can all "rally together and rise up and stand firm against the change that is depreciating our value as true artists in this unfair world" Blah Blah Blah [ Somebody please call a waaahmbulance ]. Basically they are inviting others to join them in their task of pushing water uphill with a rake.
Seriously, if you're unhappy with the fact that it is getting harder to earn a living doing something that you enjoy - welcome to reality and change your job or stop whining about it because it's just becoming irritating. We would all like to earn a living doing what we enjoy but the customers are the ones who dictate how the market swings. If you refuse to hand over the digital images to a client then there are 10 people waiting to take the job and do so instead while you argue ethics all the way to the poorhouse.

Now a prediction for the future. 4K video will mean less work/jobs for photographers, particularly wedding photographers. The customers will find out "Hey, there's this guy who can video the whole wedding and then pull still images from the video - so we don't need a photographer!" The next step will be "Well I found a guy who is prepared to hand over the entire video for us to extract the photos ourselves!" [Which they will never get around to doing but the money would have changed hands by then].
Of course the working photographers will all argue "That's 'only' 8 megapixels, we will be shooting with 36 and 50 megapixels that will blow the customers away with their quality!". Sure, that's true but what decides who a customer chooses for their wedding? maybe 1% of the weddings involve "we are prepared to pay for the best on our special day and can afford it" while the other 99% involve "We have $$$ for the food, $$$ for the venue, $$$ for clothing, $$$ for cake, $$$ for the DJ which leaves us with ?$? for photos. [photos are always at the end of their list because what good are top quality photos of hungry guests with empty plates?]
Now of course all the photographers are thinking that of course stills taken from a video will never match a well planned photo with a decent camera. BUT: The average person is so amazed by the amazing pictures they are getting from their phones and have become used to that quality, that a quick thinking videographer only has to present one or two well chosen photos printed from stills taken from a 4K video which will make the customer wonder why they would ever need a photographer when they can get video and photos from one person for half the price.
So here is my prediction: Before the end of 2015 we will be seeing the start of the blogs ranting about  how we should "stand together united as one to educate the public as to why they need a good photographer at their wedding as well, rather than relying on 'inferior' images taken from a 4K video".
Good luck pushing that water uphill with a rake - the masses have already shown us what kind of quality they will accept and when they have to choose between $4000 for a videographer and photographer compared to $2000 for a videographer that can pull stills of their choosing from the video we know which direction they will go. Then there will be the 'weekend warriors' prepared to do it for $500 of course.
Now for those of you who are saying that 8 megapixels isn't enough for top quality images please do this test. Take a photo with your 12/24/36 megapixel camera and save a copy of it while you resize that image to 1154 X 1732 = 2 megapixels as well. Print them both out at 8 X 12 inches [A4] and compare them. You will find that you can get a decent enough print from 2 megapixels so surely 8 is enough for most clients who can't afford to hire a photographer and videographer? Of course the purists will argue about the merits of the latest 50 megapixel camera [which they will be saying is not enough when 120 meg cameras come out] but the average person will be blown away by a good 8 meg image at billboard size because it's more about viewing distance than using a magifying glass - to 'normal' people that is.
So prepare to adapt to the changes that are taking place, maybe learn to do video - or start fighting for the scraps, the people who only want photos. Otherwise pick up a rake and start sweeiping that water uphill while you try to educate the public as to why they should resist progress.
 My new ebook "Introduction to flash photography"