[islandlabs] Balloon Cameras Info

Joe toolfox at gmail.com
Tue Mar 8 03:38:48 UTC 2011


On Mon, 7 Mar 2011 16:27:18 +0000
"Burns, William" <burns at cshl.edu> wrote:

> Joe:
> 
> I don't remember everything now, but my recollection was that I was
> able to use 2 IO pins to detect on/off, turn the camera on, and take
> a picture. 

That makes sense if one of the wires is used as a ground reference so
the two voltage systems are tied to a common reference. The green wire
is probably the best candidate because you need to short the white to
it to take a still picture and you need it as a reference to detect the
presence of positive voltage on the white wire (relative to the green
wire) to verify that the camera is on.

Turning the camera on might be doable if the red wire is ignored and a
positive voltage is imposed on the black wire. If we use the green wire
as a floating ground reference, that is probably how we did it before.

> I *think* it was that power could be sensed at the shutter
> button when the camera was turned on.

That's correct.

> AFAIK, we didn't monitor the
> LEDs. (or need to)

For a simple one-camera, still-photo system, we don't need to.

> Video mode may be different. not sure.

As I pointed out in my earlier message, video mode is quite a bit
different. Based on the signals we can monitor, video recording looks
no different than standby mode in terms of voltage combinations.
Observing the camera physically, the only difference in video mode
while recording is that the LED goes out; during standby, the LED
lights.

How do we know when video stops recording for whatever reason? Based on
our current wiring, I can't find a combination that indicates that.
After I send this, I'll go back to my setup and check it again.

The other big concern I have is running two cameras with a single
microcontroller as we currently wire it. Specifically, I'm worried
about tying together the two virtual reference grounds. Remember, we
also need to supply additional external battery power to run the
cameras for a full 2- to 3-hour flight. Each camera will have a diode
to drop the voltage level to one safe for the Lithium-Ion battery in
the camera. However, the two battery grounds will be tied directly
together.

It looks like I need to wire up the second camera for remote control
and rig both cameras for external supplemental power. I'll do my best
to have this ready by Wednesday for experimentation.

What do we have around in terms of small connectors that can be
soldered to a prototype board and take 30-gauge wires? I'm envisioning
this system with a connector for each camera plugging individually to a
small prototype board. The board holds the microcontroller plus an
additional connection to a battery pack that can run everything
(controller plus external supply to the cameras.

At what supply level does the ATTiny brownout? The cameras are a bit of
a load. I did test the original single-camera system from the lost
flights last year in my freezer with lithium batteries and it held up
fine for three hours at 0 degrees F.

These are some of the ground tests we need to start performing before
we can declare the system flight-ready.





Joe


P.S. -- Our fuzzy collective recollections bring to mind something one
of my bosses likes to say:

"The pen is mightier than the neuron."

Moral: We should keep more and better written notes on our
experiments...especially when we set them aside for a half-year plus...



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