[islandlabs] keycam and the microcontroller part-2

Joe toolfox at gmail.com
Thu Mar 31 22:54:12 UTC 2011

On Thu, 31 Mar 2011 04:24:28 +0000
"Burns, William" <burns at cshl.edu> wrote:

> Partial success?
> The circuit is connected to the keycam.
> It can detect the power-on/off state, and can trigger the shutter via
> the same pin.
> But... when it tries to power-on the keycam by shorting the
> power-button to positive it gets no result. If I take the
> power-button lead, and plug it directly into the microcontrollers
> positive voltage... No result?!?

Sanity check No. 1:

Is the black wire from the camera (Ground) connected to the
microcontroller's ground?

> If I unplug the microcontroller's positive battery lead
> 1) the microcontroller continues to run...
> It's drawing power from the keycam.

This would suggest that the microcontroller's supply-voltage pin is
connected to the red wire on the camera (Battery).


Any voltage over about 4.2 volts will risk damaging permanently the
Lithium-Ion battery in the camera. Using three AA batteries will
measure between 4.5 and 4.8 volts depending on age (these numbers are
for fresh, brand-new units straight from the blister-pack).

The red wire from the camera should only be fed power from the external
battery and not let anything flow back. A 1N4001-series rectifier will
both take care of this and create a voltage drop making the external
4.5-volt power source palatable to the intern rechargeable battery.



> 2) plugging the power-button lead into the positive rail will now
> turn on the keycam...

Until you use a rectifier diode, don't use the red wire -- only the
black as a ground reference between the two systems.

> Thppt!
> The intervalometer works, but...
> I can't run the keycam on external power *and* have the power switch
> work.
> But...
> The other keycam works?
> Flawlessly!

Which is which? The camera I wired up previously and brought with me
yesterday has my 16 GB microSD card in it. Call that Camera 2.

The one that you had from last year -- and I rewired yesterday --
should have your 8 GB microSD card. Call that Camera 1.

We should label them to tell the difference at a glance.

> Hrmm...
> Not sure why that would be, but at least there's one keycam working
> with still-frames. Gonna let it run overnight, and see how that goes.

Hopefully we haven't destroyed the battery!

I did test both camera control wires against the battery wires before I
delivered the second camera to you. I also tested my handiwork before
packing up my soldering equipment...although I didn't fully check the
battery connector. Granted, I did use the battery connections to verify
that the control connections operate the buttons as needed.

Unless things cure themselves, this is starting to sound like an
emergency meeting to sort out what's happening.


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