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Cameras are really not the best form of consumer
electronics to take apart, they're often pretty delicate and the
flash circuitry is at high voltage. Disassemble and modify at your
own risk!
Materials needed:
Disposable camera, soldering iron and solder, large flathead screwdriver,
precision phillips screwdriver, needlenose pliers, angle cutters,
'helping hands' or mini vise, wire, tape.
Breadboard and/or prototyping board, CMOS 555 timer chip, 47uF capacitor,
470uF capacitor, 3x 680K resistors, 1K resistor, switching diode
(1N914 or 1N4148), red LED, small toggle or slide switch.
- Disassemble the camera:
Take the camera out of the packaging, take out the batteries,
remove the 3 screws that hold the body together. Take off the
back cover, being careful not to touch any of the electronics
on the inside (they may be at high voltage), and put the plastic
case aside.
- Discharge the flash capacitor:
Carefully hold the main PCB board as shown, preferrably using
a 'helping hands' tool or vise. make sure the jaws don't short
any exposed components.
Note the large capacitor, when the flash is charged, this capacitor
has 450V across the leads. Before any hacking can be done this
capacitor must be discharged safely. Holding the large flathead
screwdriver by the plastic handle, touch both capacitor leads,
there will be a large pop and flash as 3300uF discharges across
the screwdriver tip. Electrolytic capacitors can hold their charge
for a surprisingly long time, and they also exhibit "dielectric
soak" where they appear to 'recharge' themselves (see Sprague's
explanation.) For these reasons,
you must always discharge the flash capacitor
before you start working with the board, even if its been unused
for a long time, and every few minutes while the circuit is being
worked on.
- Attach the control and power wires:
Cut 3 wires (preferably 22ga or thinner, stranded core) in three
different colors, two of which are red and black. The red wire
will carry +3V, the black wire is the common ground, and the third
wire is the shutter signal wire. Strip the ends, and tin them.
Solder the wires to the pins where the main board connects to
the flash board. Staring from the shutter button, the black wire
connects to pin #4, the shutter wire to pin number #6, the red
wire to the last pin, #8.
Thread the wires through the small hole in the flash board. Put
the plastic case back on, so that the wires come out the side
of the case.
- Reassemble the camera:
The case won't close all the way, so don't try to or you might
break the case or cut through the wire insulation! Insert the
two screws near the bottom of the case, and use a piece of tape
to secure the top.
- Build the controller circuit:
You might want to start out by building it on a solderless breadboard,
and seeing if it works properly, before soldering it on a perf-board.
Be sure to use a CMOS 555 timer chip, such as the TLC555 or the
LMC555. Other chips, such as the NE555, LM555, etc. will not work
at 3V power! Also note that the LED, diode, and capacitors are
polarized, and wont work if they're plugged in backwards. Electrolytic
capacitors have a marking on one side (usually a negative sign
next to the negative lead). Diodes have a painted stripe on the
negative side, which is the end that the 'arrow' in the symbol
points to. LEDs differ, sometimes they have a flattened side,
or if you can see inside, there are two parts, one that looks
like a 'cup', this is the 'negative' side, or the side the arrow
points towards. Another good way to test is to connect the LED,
briefly, to the red and black wires coming out of the camera,
it will light up when the negative side is connected to the black
wire.
VCC in the schematic will connect to the red wire coming out of
the camera, GND is the black wire and the output goes to the shutter
trigger wire.
- Test the circuit:
Connect the red and black wire from the camera to VCC and GND
of the circuit. After 2 or so minutes, the red LED should light
up, after about a minute more, the red LED should go out. The
LED will then flash on and off, about once a minute for a full
cycle. (The first time the LED lights up will be longer than the
other times, so dont count that when timing the LED.) If the circuit
is working, first check that there is 3V between the red and black
wire. Then use a multimeter to check the voltage across the 470uF
capacitor, it should slowly rise from 0V to 1V or so, then jump
up to 3V. If it isnt slowly rising, make sure the diode isn't
backwards. Once that is working, check the voltage across the
47uF capacitor. Once the reset pin is above 1V, the capacitor
should slowly charge up to about 2V and then discharge to 1V,
then up to 2V, etc. If that's working correctly, check if the
LED is in backwards, or if it's not red, amber, or yellow. Try
removing it and checking the output pin voltage. It should flip
between about 2V and 0V, one cycle per minute.
- Adjust the circuit (if desired):
By swapping in larger resistors, you can extend the delay times.
To make the startup delay longer, swap out R3. To make the between-pictures
delay longer, swap out R1 and/or R2. Make sure that from when
the circuit is turned on, the LED lights up and goes out within
3 minutes, so that the camera doesn't automatically turn off before
you want to start taking pictures.
- Rebuild the circuit on solder prototyping board (perfboard)
so its more durable (optional):
Since you can't disconnect the power wires, be sure to solder
in a switch so you can turn it on and off. Test it again to make
sure the LED blinks at the desired rate.
- Test out the full system:
While the board is
off, discharge the two capacitors with the screwdriver to make
sure they start at 0V. Connect the trigger wire to the output
line of the 555. Turn on the circuit, then turn on the camera.
When the LED turns off for the first time, the camera should take
a picture. (If it doesnt take a picture, try connecting the trigger
wire to the black wire. If it still doesn't take a picture, then
you probably didnt solder the trigger wire to the right pin.)
- Take flight!
Mount the camera and control board
to your kite.
- Disconnect the control circuit and develop images:
Once you've
taken all the pictures you want, land the kite, and check the
"Pictures remaining" counter to verify the circuit worked.
After all the pictures are taken, disconnect the circuit by opening
the camera, discharging the flash capacitor, and desoldering the
wires. Reassemble the camera and have it developed where it was
purchased.
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