There are two circuits in this project, the camera trigger and motor control.
I use a Sony DSLR which has a port to connect a remote trigger. This has three pins - ground, autofocus and trigger.
There are some good sites with details of various manufacturers camera ports, notably this one.
The first step was to work out which pin was which. Using an old computer connector from a cd drive plugged into the port I was able to determine the first two pins were ground and autofocus. My camera needs the autofocus connection on before it will allow the trigger input to fire the shutter (regardless of whether I’m using autofocus or not).
So, I wire pin 1 and 2 together, allowing the camera to trigger by connecting the third pin to the joined 1 and 2. Result!
To trigger this from the Raspberry Pi I use the GPIO pins to control an NPN transistor, acting as a switch.
I used some transistors I had lying around, but 2n2222a NPN transistors should be a good choice for this.
470r resistors should be fine for these circuits too.
The basic circuit looks like this:
The resistor is in place to limit the current between the Pi and the transistor.
Again, a switch is needed here, so the above circuit is repeated for the motor. However I’ve added a diode to protect the Pi from current generated by the motor when the power is cut but the motor still turns a little.