Intervalometer is an automatic finger for the camera trigger that never gets numb or falls a sleep. (Understatment?)
Even though they are commercially available two issues rise for me;
1) They are ridiculously expensive!
2) They are designed mostly for SLR's. (Also compact cameras are not designed for them)
Particularly the second one bothers me more because i want a lightweight KAP rig and honestly, i can not risk my SLR to fly on few millimeters of dacron/nylon/kevlar. So, after deciding to use my existing Canon C360 compact camera next step was to find a way to trigger the shutter remotely or automatically. This led two more issues.
1) The camera does not incorporate a remote trigger system (Cable or IR)
2) More sophisticated: The camera simply does not have fixed focus! So everytime it takes a photo in whichever mode, it needs a "half-press" and wait until the green box appears (e.g. focused) and then release the shutter, a "full-press".
1)Modifying a compact camera for remote shutter release
WARNING: DISASSEMBLING A COMPACT CAMERA EVEN WITHOUT THE BATTERIES IS DANGEROUS!
FLASH CAPACITOR IS VERY LIKELY TO BE TOPPED UP TO FEW HUNDRED VOLTS!
DISCLAIMER: Don't blame me if you mess up your camera...
1st issue was not much of an issue indeed. I'm on/off electronics enthusiast and i LOVE disassembling and re-assembling things, particularly discovering how much "extra" components and screws the producer put into. A tiny philips screwdriver was enough to undress the camera body. Then i soldered really thin (36 awg?) insulated wires to shutter/focus switch of the camera. It was pretty easy to figure out:Grounding the focus lead takes the camera to focus mode and while it is still grounded, shutter lead is grounded and voila! Lightly twisted the cables and routed near the SD/USB bay, fixing here and there with drops of cyanoacrylate. It's important to pay extra attention to routing procedure since most compact cameras are meant to be compact and it can be tricky to put things back together. But i'm pretty sure that even the smallest camera will have place to route hair-thin wires.
Next step was to make/find a connector. A glimpse at my slr revealed that the connector is identical to "jumper" type pins sticking out. So salvaged few pins from my ancient ISA graphics card (remember them?) and soldered to a tiny veroboard. Filed/sanded to the smallest footprint possible. Glued to its place with a dab of 5 minute epoxy. (Not CA, i needed serious gap filling glue). The only pitfall was the removal of the SD/USB bay door because the pins protrude outside the case. I don't thing it's a major problem. I expect to find some more dust next time i disassemble the camera, nothing more.
2) Focus/Shutter Timing for Intervalometer
The separate focus/shutter switching is more or less particular to my camera. Kodak C360 required 2 seconds (roughly) in the worst case to set the focus and shutter speed. Mostly the autofocus works less than 500ms but to be on the safe side i went for 3 second focus trigger. For the shutter release, the length of the pulse is not so important. Not tested but likely 100ms or even less will release the shutter. Also I don't know the specifications of other cameras but maybe as a coincidence my slr seems to work with very similar timings. Newer cameras have way faster A/F measurements but i assume they are not bothered by longer "half-press" durations.
Existing intervalometer designs use wide range of approaches. From 555 to microcontroller based opto-coupled devices. But apparently no one seemed to be dealing with the problem i had to (i think there are some expensive intervalometers with a lot of options but they are well beyond the reach of hobbyists.) And my design criteria was as follows;
My final version is slightly outside these design objectives but works. It would be better to design it with a NAND gate but i already had 4081 CMOS quad AND gate ic. So i went with it. Before the schematic, a brief explanation. The circuit can be divided to three sections. A timer (astable multivibrator) that creates a 3 second pulse per each interval. A second stage to buffer the signal,create delay for the shutter signal and synchronize "removal of finger" to prevent false triggering the shutter twice. Last stage is basically a transistor switcher, one for focus and one for shutter. It's build on a piece of veroboard and capable of being powered from the camera itself of a junk Li-Po battery salvaged from a dead R/C Helicopter.
I'm pretty sure this circuit lacks proper techniques. I've only basic electronics knowledge, it's just a hobby for me and of course this circuit can be improved or designed in a better way by professionals. For me, i needed something that'll work, and it is.
I don't have a schematic drawing software and was lazy to install one only for a single schematic but i have the photo of the hand drawings. (TODO)