[Stratos Burst] Camera and software

In order to continuously capture images during the ascent and the free-fall afterwards, the camera on board will need to use an intervalometer that is programmed to trigger shots automatically. Instead of adding additional equipment that will increase the payload weight, we have elected to use an inexpensive point-and-shoot camera that can be hacked with an open-source script add an intervalometer to the camera features.

The Hack
CHDK is an open source program that can be added to your Canon camera, and introduces a range of features. What we're interested in here is the ability to add custom scripts to the lineup. (CHDK Wiki)


The wiki also provides a list of Canon model numbers that have proven compatible with the update as written. We're using this to narrow the search for an affordable camera.


The Ultra Intervalometer script allows you set the interval to your first shot, the span in between each following shot, and the number of total shots, or just make it endless. This means that so long as the camera has power and memory, it will take shots as often as you tell it to. There will be some calculations done later regarding the expected flight time, memory, approximate size of each image, and interval so we can plan on getting as many shots as possible throughout the flight without running out of memory.

Cost: Free

The Camera

The camera will likely be the largest purchase we could make for this project. The first one that we considered for this was a Canon Ixus 70. We already have one that we have used for several years. The wife has been hinting at wanting a new digital camera anyway, so if something fatal happend to it during the flight (or more likely -- the landing) we wouldn't feel put out by the loss. Unfortunately it uses a NB-4L Lithium-ion rechargeable battery. In this situation that is a deal breaker. We really want to use standard Lithium batteries in all electronics where possible. It gets really cold up at the altitudes we expect to reach, and those temperatures can cause NiCad and Li-ion batteries to shut down. It's unfortunate, but Li-ion batteries are just too weak. We do plan to include a couple of pocket hand warmers in the payload to keep the internal temperature of the insulated container up, but as a redundancy Lithium batteries can tolerate lower operating temperatures.


Next we found a used Canon Powershot A470 on Craigslist for $90. This was local and was on the list of cameras compatible with the necessary firmware hack. Unfortunately it is not listed on the list of tested models that work with the intervalometer script. Now that is not to say that it won't work, but if it did not, I'd be out that cash for this project.


Instead, I have opted for a Powershot A480 which is on both the firmware hack and the script list of verified models. I found a used one on Amazon for approximately the same cost, and it sports 10 megapixel resolution instead of the A470's 7.1 megapixels. This should hopefully lead to sharper images throughout the flight. It is also powered by two AA batteries, which allows the use of off-the-shelf lithium batteries.

Cost: $55.00


Batteries
I picked up a 4-pack of AA lithium batteries. Two will go into the camera on flight day. I expect that the other two will be used as a backup power-source for the prepaid phone that will be used to help us retrieve the payload when it returns to terra firma.


Cost: $11.99 + tax


Edit: Ok, bugger this. The vendor I bought the camera from cannot find it now, so I'll have to look someplace else. Hello, ebay.

Edit: Ok, after a series of lost auctions on ebay, we've managed to secure a "like new" model A480. Now, onward!


Edit: 17 May 2011. For once the USPS managed not to lose something bigger than a letter, and the A480 showed up today. I'll be posting on my progress of hacking it and loading the intervalometer script soon.