[islandlabs] Balloon Cameras Info
jonathan at jedahan.com
Mon Mar 7 05:00:16 UTC 2011
You can always pull an atmega168/328 off of an arduino deumilanove. Sure its
a bit more expensive than an attiny45, but if time is of the essence you get
28+pins right now. If no one has a spare I can find one lying around -
simplicity > optimization for stuff like this.
On Sun, Mar 6, 2011 at 6:13 PM, Joe <toolfox at gmail.com> wrote:
> Today I started digging into the keycams that Bill and I were tinkering
> with last fall. One camera was wired up with four external connections
> from the two switches, so I dismantled it and made notes on the
> The four wires are paired red/black for the power switch and
> white/green for the shutter/mode switch.
> With the unit off, there is (with a full charge) 3.26 v across the
> red/black pair (red positive) and 0 v across the white/green pair.
> Cross-checking the other combinations (red being the only apparent live
> wire), I got 3.00 v across red/white and 3.28 v across red/green.
> There is no direct continuity between any two pairs in any combination,
> indicating that there is no common ground amongst these wires.
> Shorting the red/black wires naturally turns the system on to standby
> mode. By extension, the shorted wires will obviously be 0 v across them.
> Once on, the red/black wires remain with the same 3.26 v potential
> across them. However, the white/green combo now has 3.27 v (white
> positive), indicating that the system is on.
> So, for a microcontroller-based control system, the white wires must be
> sensed for positive voltage or a logic "1" to indicate that the camera
> is up and running. This is true whether the camera is taking still
> photos or video. Of course, the white/green combination needs to be
> activated for each still picture and can't be sensed while "pressing"
> the button.
> For complete disclosure, the red/white combo yielded 0 v, and the
> red/green read 3.28 v (red positive) with the camera powered up.
> I have no connections for the camera's LED. If we bring this signal out
> as well, we might be better able to deduct the camera's state at any
> time. But let's see what we can with what we have.
> To power up initially, we need to short the red/black wires
> momentarily. No other useful information on camera state can be
> gleaned from these wires, so perhaps a simple
> transistor-based optoisolator will do. This will use one I/O pin and
> doesn't need to worry about electrical reference grounds between the two
> Similarly, the white/green wires can use a second optoisolator so
> starting the video camera or taking a photo with the still camera will
> consume a second I/O pin.
> To sense a failure mode of the camera shutting off, we need to see a
> difference signal. One choice is the white/green pair with either using
> green as a ground reference and sensing voltage on the white (positive
> voltage=camera on; no voltage=camera off) or connecting yet another
> optoisolator across the white/green wires in an inverse pattern.
> Using a third optoisolator avoids struggling with ground references (I
> keep mentioning this for a reason that I'll get to later), but might
> interfere with operation of the camera's switch input due to the
> increased current load across the wires from the optoisolator's inputs.
> This needs more experimentation.
> At this point, we've used three pins: Power switch output, shutter
> switch output, and shutter voltage input. Running two cameras off one
> controller will use 6 pins, which on an ATTiny can theoretically be
> If, on the other hand, we combine the two shutter switch optoisolators
> in some way that they don't feedback on each other, we can reduce the
> the I/O pin count to 4: 2 for each camera.
> I'm not coming up with any solutions on this approach. Personally, I'm
> leaning toward the 3-pin design.
> This method of sensing camera state should be fine for the still
> camera, but what about the video camera? If the video camera stops
> recording and goes back to standby mode, the signals we're monitoring
> will not show that anything went wrong!
> The only indicator of coming out of video mode is the camera's LED:
> It's out during recording and on during standby. Similarly, the
> still-photo mode turns the LED off during photo capture and turns back
> on after the image has been red from the CCD.
> We want this system to be as robust as possible: we can't allow for
> errors at 98,000 feet.
> I think we should look to monitoring the LED as well. This means one
> I/O for the power switch, one for the shutter/mode switch, one for
> verifying that the camera is turned on, and one for watching that the
> camera is properly collecting visual data.
> We've overrun our allotment of I/O pins.
> We're going to need two ATTiny controllers or a larger controller
> (An ATMega? One of the PICs we have floating around?).
> If we place an order with Jameco Electronics, it'll be a week for the
> package to arrive on the East Coast. We could also look into ordering
> with Mouser; shipping from Texas will be here in three business days.
> Bill, I know you were finding some of these error modes with the camera
> shutting off. What approach were you using when you were breadboarding
> this system?
> I'd like to get this system ready for stress-testing by next weekend if
> possible. That will bring us into the second week of March.
> Time's moving on...
> List mailing list
> List at freeculture.org
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