##Introduction##
To get the cameras to trigger simultaneously, we chose to trigger them via USB using a feature of the CHDK.
##Assembling the 555 circuit##
* Pretty good instructions come in the 555 timer package
* Potentiometer confusion
* Stripping and attaching the USB cables
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##Connecting the batteries##
###Battery selection###
* Two different batteries are needed:
* a 12 volt battery to run the timer, and
* a 5.5 volt (or more) for actually triggering the camera.
To keep things simple, and because it's hard to find an efficient, cheap and lightweight way to hold 4 cell batteries, here we show how to fit 4 coin cell batteries into an N-type battery holder, which is provided in the dual infrared kit -- using a small wood screw.
This is a bit of a "hack" but has worked very well - 4 1.5 volt batteries is ~6v and very little current is needed to actually trigger the camera.
###Attaching to the 555 timer (extra wire)###
(coming soon)
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##Splicing USB cables##
Using a wire stripper, cut at least 8 inches of USB cable, preserving the smaller connector. Strip off the plastic wrapping to expose the smaller wires within and trim away the foil, fine metal strands, and the green and white wires. You'll want more extra wire than shown - maybe trimming to leave an inch of exposed red and black wires will give you some working room. Do this for 2 USB cables, identically.
Now, you can take both red wires and the red wire from one of your (N-type) battery holders, twirl them together, and solder them together firmly. Do the same with JUST the two black leads from the USB cables.
You should be left with two loose black leads: one a combined lead from the USB cables and one from the other end of your battery holder. Place them into the headers of the 555 timer as shown and screw them into place (the screws will hold the wires firmly in the headers.
Here are a couple images of the whole setup:
