How to Trigger a Custom Accessory Using a DSLR Camera Hot Shoe Connection?

I want to create an accessory for Digial SLR cameras that would attach to the 'Hot Shoe' located on the top of the camera where a flash would be attached. I was wondering how I would go about creating a connection between the hot shoe and the device.

Ideally, the device would be activated once the cameras shutter is pressed halfway down, just like the flash attachments are activated threw the hot shoe.

I have purchased a few materials for putting together my prototype, but am stuck at how to get this connection to work in the way I'd like.

Any advice would be greatly appreciated. I will also be looking for an individual or small company to help take this to the next level after i develop my prototype.

Thank you

The circuit would consist of a voltage detection circuit followed by an output circuit. I suspect there is an official or a defacto standard for the shutter button halfway press and full press. The voltage detection circuit can consist of two comparators that reliably sense the two shutter conditions. The output circuit is then designed to output whatever voltage you want into the desired impedance.

Here is a link to the Wikipedia article on hot shoe voltages: http://en.wikipedia.org/wiki/Hot_shoe

If you are designing for a specific camera manufacturer the hot shoe voltages can be obtained using a digital oscilloscope. Designing a universal device - one that works with all camera types - is more difficult. Two ways I can think of off hand to handle this are with a manual selector switch or a device that had a "learning mode." The first way can be done with analog circuitry while the second way is best done with some digital circuitry.