Those looking for a simple means to click the shutter of an SDM- or CHDK-controlled camera might want to take a look at these
. Although it talks about interfacing to a basic stamp, all you need at the camera end is a 5v supply and the receiver, I haven't measured the range yet, but it will certainly operate cameras atop my carp pole.
The receiver board has 7 pins:
1. 5v power
2. output voltage (connected to one of the output pins via radio)
3. common ground
4-7. 4 output channels
The 4 buttons on the transmitter connect (on a push) or disconnect (on the next push) pin 2 to one of the 4 output pins. While this does nothing that you can't do hacking a wireless doorbell, the amount of work needed to produce a working control is minimal - it took me just a few minutes of soldering to wire the receiver board to a USB connector (to plug into the camera) and a servo connector (to plug into a 4-cell AAA power supply). The board weighs just 5 grams - less than the two connectors!
Here's the circuit I built: