I was wondering if anybody knows of any software for a computer that would use a webcam to monitor an area and tigger a DSLR to take a picture when motion is detected?
I'm using a Canon T2i and a windows 8 computer.
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While this solution does not use a webcam, it does what you want.
The Magic Lantern custom firmware can be downloaded for free and includes, among many other interesting features, motion detection functionality.
The firmware is not installed on the camera but on the memory card. If you don't like it, just format the memory card.
It supports a wide range of Canon cameras, including the Canon T2i/550D.
The CameraAxe will let you trigger your camera from nearly anything, sound, light, lightening, movement, etc. Its available as a kit or completed.
While not using a webcam per se, the CHDK = Canon Hack Development Kit could be used for your task with relative ease.
On cameras which it works with, CHDK allows flexible control of all camera features.
CHDK will not run on the t2i directly, but it can be used on many Canon 'point and shoots'. As you have control of USB functions and other features a means should be able to be found to use a cheap Canon point & shoot as a trigger source in the same way that you suggest with a webcam. Later camera models may not work but extensive details and compatibility lists are available. CHDK loads on an SD card which is read by the camera at powerup and used to temporarily load the program to camera memory. The load is transient, being limited to the current power-up session and causes no permanent camera changes.
CHDK can control just about any camera controllable feature and can output data on the USB port. This could be used with relatively simple hardware for camera control. CHDK allows eg defining a window within its view area and capturing images or performing other functions when motion is detected.
Using a CHDK equipped camera to trigger a DSLR flash:
There are many possible ways. Here are two -
(1) Use remote flash sensing trigger module on DSLR -
Trigger flash on CHDK camera to optically trigger DSLRs.
Can be arranged if desired so that CHDK camera flash does not illuminate main target.
(2) Obtain optocoupler requiring a few mA input current, bipolar or MOSFET transistor output. (1-5 mA best, 5-10 mA should be OK, much gigherworks but unneeded.
Place opto coupler input + resistor to suit desired current from USB+ to gnd on CHDK camera USB connection.
On motion detection, trigger initiate CHDK camera USB action - can be anything that toggles USB+. For opposite "sense" use USB- to ground.
Use opto output in any of the circuits available on web for camera triggering via external trigger socket. There are many and nominating any one is pointless. Opto ouput acts as a single pole single throw switch.