##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##

* 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)