David,
Good idea.
Looking at the S3IS you have given me an idea which may work.
There was a discussion on the CHDK Forum a while ago about mounting
led detectors to a camera.
In my region could not find any suitable detectors or mounting equipment.
The reason I used the VOX approach was that a VOX kit was available at
the local electronic shop.
http://www.jaycar.com.au/ CAT. NO. KC5172 Cost $15.95
The ease of mounting an electret microphone on an L bracket made it attractive.
The camera speaker has a fixed frequency.
The microphone will only pick up the speaker beep when mounted next to
the speaker.
The electronics filters any unwanted frequencies.
If anyone else is having problems with the led approach; I can
recommend the VOX unit.

Sometimes it is easier to give up and use a manual system like the
laser level mount.
I have a neck and back injury which causes me problems plus I am
finding the bright summer sunlight make it hard to see the ELV and
LCD.
I am interested in the Picaxe approach. Picaxe chips are readily
available in my region.

On 7/3/09, David Sykes <killspammers2@...> wrote:
> John Fimognari wrote:
>
>> I assume that David has found a way of sending a pulse down the USB
>> line
>
> No, I flash the LED.
> I have made a neat plug-in photodetectot that is positioned over the Direct
> Print LED.
>
> I have covered it with an extremely dark blue filter that only passes 1% of
> the visible spectrum.
>
> With LED off, output was a few mV.
>
> With LED on, output was full scale.
>
> Outdoors in direct bright sunlight with LED off output was full scale !
>
> The way to really do this is to add a socket across the LED.
>
> For your use, the item I gave the link for is not really suitable, you need
> something far more highly engineered.
>
> Nevertheless, the camera to Picaxe features should still be of interest.
>
>
> David
>
>