##Introduction##

To get the cameras to trigger simultaneously, we chose to trigger them via USB using a feature of the CHDK.

<a href="https://www.flickr.com/photos/jeffreywarren/6935669297/" title="Dual camera 555 trigger by jeferonix, on Flickr"><img src="https://farm8.staticflickr.com/7053/6935669297_7f27683c21.jpg" width="500" height="375" alt="Dual camera 555 trigger"></a>

##Assembling the 555 circuit##

* Pretty good instructions come in the 555 timer package
* Potentiometer confusion
* Stripping and attaching the USB cables

<a href="https://www.flickr.com/photos/jeffreywarren/6935669735/" title="Dual camera 555 trigger by jeferonix, on Flickr"><img src="https://farm8.staticflickr.com/7065/6935669735_fdd64f4002.jpg" width="500" height="375" alt="Dual camera 555 trigger"></a>

![Battery "hack"](https://publiclab.org/sites/default/files/imagecache/default/IMG_0033.JPG)

##Connecting the batteries##

<div class="caption right">

<a href="https://www.flickr.com/photos/jeffreywarren/6983498676/" title="5 coin cell batteries + 1 screw fit in the holder by jeferonix, on Flickr"><img src="https://farm8.staticflickr.com/7211/6983498676_eb3f02dec6_m.jpg" width="240" height="180" alt="5 coin cell batteries + 1 screw fit in the holder"></a>

<a href="https://www.flickr.com/photos/jeffreywarren/7129585053/" title="Place them inside one by one by jeferonix, on Flickr"><img src="https://farm8.staticflickr.com/7064/7129585053_ff0a8f520f_m.jpg" width="240" height="180" alt="Place them inside one by one"></a>

<a href="https://www.flickr.com/photos/jeffreywarren/6983501162/" title="Four should fit snugly and securely by jeferonix, on Flickr"><img src="https://farm9.staticflickr.com/8019/6983501162_ed148d2cfb_m.jpg" width="240" height="180" alt="Four should fit snugly and securely"></a>

</div>

* 2 different batteries needed: 12v and 5.5v or more
* Fitting cell batteries into N-type holder (hack)
* Attaching to the 555 timer (extra wire)

##Splicing USB cables##

Image dump:

<div class="caption right">

<a href="https://www.flickr.com/photos/jeffreywarren/6983507076/" title="Snip the USB cable to at least 8 inches long by jeferonix, on Flickr"><img src="https://farm8.staticflickr.com/7236/6983507076_de56036678_m.jpg" width="240" height="180" alt="Snip the USB cable to at least 8 inches long"></a>

<a href="https://www.flickr.com/photos/jeffreywarren/7129595197/" title="Separate out the wires from the wrapping by jeferonix, on Flickr"><img src="https://farm8.staticflickr.com/7071/7129595197_011c38669d.jpg" width="500" height="375" alt="Separate out the wires from the wrapping"></a>

</div>

<a href="https://www.flickr.com/photos/jeffreywarren/6983512146/" title="Snip off all but red and black; strip off their wrapping by jeferonix, on Flickr"><img src="https://farm8.staticflickr.com/7111/6983512146_c1444df2e9.jpg" width="500" height="375" alt="Snip off all but red and black; strip off their wrapping"></a>