The other day I posted about progress on an aerial photography project.  At the end of the day, my auto-picture-snapping circuit didn’t work.  It’s my first project using a 555 timer (NE555P).  I finally measured the capacitance of the timing capacitor and found it was WAY smaller than I’d thought.  The circuit output seemed to be always high because the frequency was really high.  This also explains the low voltage (averaged over duty cycle)!  I swapped the capacitor with one closer to my design and it flashed LEDs just right!  When I connect the camera up to the MOSFET (2N7000) that is controlled by the output of the 555, I got pictures!  Woohoo!  You should have seen my excitement when it finally worked…actually you can!

it works!

Advertisements

Since our church is not too strong in the revenue department, we try to get creative with fund raisers in order to bring as many people as we can to camp.  This year, we collected stuff for a yard sale and did pretty well.  Our enchilada sale was a success, too.  But we’re still coming up pretty short.  I got the idea to sell personalized aerial photographs that we could take using a tethered balloon.  I’m still not finished with the setup and camp is this weekend, but I think it could be a pretty good little racket.

The plan is to get a cheapo camera that I can wreck without too much heartache (craigslist camera – CHECK!) and send it up with a helium balloon and a picture-taking circuit.  I estimated (assuming ideal gas law and spherical balloon) that a 36-inch balloon could lift about a pound.  I found a website with 36-inch balloons six for $10.  This seems so easy and simple!

I spent a few hours in the middle of last night working on the picture-taking circuit part.  I made progress, but in the end I was pretty disappointed.  I was able to crack open the camera after an hour of ridiculously excessive straining with the wrong-sized screwdriver.  I poked around with some wire to figure out which metal pieces need to connect to trigger the shutter.  Then I soldered wires onto each side of the connection that worked.  After running the wires out of the camera and closing the camera back up, I tested it out by touching the loose ends of wire together and BAM!  There you go – it worked!  This is great, because now it should be really easy to trigger photos with an easy-to-generate signal from a simple circuit or a microcontroller like the Arduino!

I recently bought a hundred 2N7000 MOSFETs from Jameco.  It seems to me that one of these is perfect as a switch to short my two shutter-control wires together.  I also bought a hundred 555 timer chips…because I’m crazy.  But one of these should come in handy to send a shutter-control signal to the MOSFET switch every few seconds when the camera is in the air.  I referenced a handy LM555 calculator website to build this circuit (powered by an ATX power supply for testing):

555 timer circuit for camera shutter control

I tried to size the resistors and capacitors for the 555 timer to generate a periodic square wave signal with about 0.15 seconds of “on” followed by 15 seconds of “off”.  It didn’t work!  When I tried it with 5V supply, my multimeter shows what seems to be a constant 1.9V output from the 555 (Vgs on the 2N7000), which results in a partially on MOSFET with channel resistance around a k-ohm instead of just a couple of ohms.  With 12V supply, I get Vgs of 6V but it seems to have 100% duty cycle (the “pulse” to signal the camera is always on).  I might as well not have a 555 chip in there – no good.  This is the point in the story when I realized the sun had come up and it was time to go to work.  Will need to face this later, as well as the issue of supplying power at 5V or higher when the camera has a 3V supply.