Edit (3/29/2014): When I first posted this instructible earlier this month I didn't describe what I was going to be using this rig for or where my requirements were derived from, but now that I have gotten some film back I thought I would share.
I needed a way to take low volume high resolution photos of liquid rocket launches and static fire (hold down) tests in the Mojave desert. Last weekend was my first opportunity to photograph such tests with this wireless shutter release on my Pentax film camera and I was very pleased with the results. I have added a results section at the end of this instructable that reflects some of my lessons learned from that weekend.
I needed to take high resolution photos remotely with my Pentax 645 medium format film camera. I could not find any off the shelf solution, let alone one that meet my requirements, so I decided to build my own.
Any small enclosure will work. I selected the small plastic model from Adafruit because I was already ordering parts from there and I liked the captive screws. I always recommend plastic enclosures for electronics projects because they are easier to machine, and there is less risk of shorting out components due to conductive FOD; the modem will also have trouble transmitting out of a completely metal enclosure.
Series 1 xBee Modem with Wire Antenna
Are xBee units overkill for this simple 1 channel DIO line passing project? Yes, they absolutely are, but the environment it needs to operate in will have many other RF sources on bands that I can not always know ahead of time. The xBee modems use packetized transmissions that are unicasted to specific modem, this makes it nearly impossible for to recieve a false positive signal and actuate the shutter. This also provided me my first opportunity to learn how to do DIO line passing with an xBee modem, a very handy feature which I explain in great detail in a few steps. If you are looking for a less robust and much cheaper RF transmitter option sparkfun has a few options here, here and here; I can't vouch for them, but if you use them successfully post a comment and let us know how they work.
If you want more range and power consumption is not a constraint to your design you could also get the Series 1 xBee Pro which has a Line Of Site (LOS) range of 1 Mile, compared the regular xBee (which I used) with a LOS range of 300ft. If I ever need more range I can easily swap out my current xBees for xBee Pro's because the adafruit adapter can accept both.
Wire (whip) antenna vs. Chip Antenna - Wire (also know as whip) antennas will get you better range, reference here figure 1 on page 3.
Unless you have a special application only get "Series 1" xBee modems, not Series 2 or ZB or any other types.
Any xBee adapter will work, I just prefer the one that Adafruit makes. Sparkfun also sells one here.
FTDI Interface to configure xBee
You need some way to connect the xBee unit to a USB port so you can configure it. There are many different flavors of these, but I prefer the one that Adafruit makes because it simply plugs into their xBee adapter. Sparkfun also makes one here.
The shutter release cable does not require a great deal of throw or force to actuate the shutter, so nearly any servo should do the job, I selected this primarily due to its small size.
The microcontroller doesn't need to do much, it only needs two DIO pins and a servo library. The Adafruit Trinket fit the bill perfectly and only cost $8.
7.4V Li-Polymer Battery
Any batteries will work as long as they fit your power budget and size constraints. I had one of these little Lithium batteries from Sparkfun lying around so I used it. I did buy a back-up AA holder just in case I ran into trouble here. I also used a 8.4V Ni-Mh battery for my remote (sensor) node.
Shutter Release Cable
No special requirements here, unless you want it to look extra cool, then get it in red.
I got one free with may Adafruit order. Now I see why she gives these way, they are pretty nice will need to order more. You will need two, one for the sensor (remote) node and one for the base (camera) node.
Wire to board connectors
Use whatever flavor you prefer, I had these big screw terminals lying around so I used them. If I was to do this again I would have used these.
Wire to wire connector
Once again whatever flavor you prefer, I had 0.062" Molex connectors on hand, so I used them.
Whenever I do board level work I try to use the nice stuff: Mil-Spec M22759/16.
Hot Shoe to 1/4-20 adapter
This is how we will mount the box to the top of nearly any film camera.
5V Linear Regulator
To regulate the battery voltage down to 5 volts.
You need one 10k resistor to pull up (or down) the DIO7 pin on the remote (sensor) node, because it does not have an internal pull-up.
1. Soldering Iron
3. Assorted drill bits, up to 1/2"
4. Dremel with cut-off disks
5. Wire stripper
6. Diagonal Cutters
9. Windows Computer
10. Small piece of plastic, wood, or rigid foam
11. Epoxy / Hot glue
12. Super Glue