Mini Slave Flash

What Good Is It?

Photographers use things like this to provide additional light from different angles when their main strobe goes off.

The best way to do this is to scavenge the parts from the strobes of disposable cameras and use those as the heart of the project, by turning them into slaves.

NOTE: I haven't built one of these yet! The theory is sound, but has not yet been tested!

Salvaged disposable camera

Safety precautions

Flash circuits work by generating a high voltage, storing it for later in a capacitor, and discharging it all at once. The high voltage is potentially dangerous and the sudden burst of energy from the capacitor is potentially lethal.

The combination of high energy and sudden release thereof make flash circuits tricky to handle. Know and follow the precautions appropriate for high energy electronics.

Once the strobe circuit board is exposed, it is easy to stay away from the dangerous parts, because all the parts are dangerous!

While the disposable camera is being dissected, take care that you don't touch the circuitry by accident. It might be a good idea to wear rubber gloves during this process. Eye protection is a good idea, in case plastic parts or springs jump out.

Avoid touching the flash lamp's glass envelope with your hands. Skin oils will stay on the surface, trap energy, and cause hot spots that might cause the lamp to shatter.

Do not look directly into a flash lamp as it fires. The intense light, rich in UV, can damage your eyes.

Selecting a disposable camera

There are numerous manufacturers and models of disposable cameras. They are probably all convertible into strobes, differing only in the nature of the changes necessary to do the conversion.

In order to be able to provide exact directions, this page deals with just one particular model, the "Kodak FunSaver 35 with flash", circa 1997. The camera is 120 mm wide, 55 mm tall, and 30 mm deep. The plastic body of the camera is boxy, with square edges. The body is enclosed in a cardboard box. It has a switch that you slide and hold to charge the flash.

The page does not deal with the "Kodak FunSaver Pocket", which is slightly smaller, has rounded corners, and has the plastic box partially wrapped in a sticker instead of a cardboard box. The FunSaver Pocket uses an entirely different flash circuit. You press a button to start the charging process, and the camera recharges itself after every shot. The automatic recharge is fine, and the camera will probably work here, but I don't have explicit dissection instructions.

If your camera differs in any way from the one described in this page, you may have the wrong model, or Kodak might have changed their design. In such a case, you are on your own. Proceed with extreme caution.

Salvaging the flash electronics

• Remove the plastic camera body from the cardboard box. Discard the box.
• Check the battery compartment in the underside of the camera. If the battery is missing put one in; a 1.5V AA penlight cell, a picture engraved on the case shows which way it goes in.
• Find the "charge" switch on the front of the camera and slide it to the "on" position and hold it there.
• Watch the "ready" lamp until it goes on and stays on steadily.
• Release the "charge" switch.
• Now remove the battery and save it for later use in some other project.
• Point the camera away from you and release the shutter. The strobe should flash and the "ready" light go out.

This accomplishes two things: we now know that the unit contains usable parts; the energy storage capacitor in the strobe is now mostly discharged.

It is time to dismember the camera. This is a good time to put on rubber gloves. The energy storage capacitor in the strobe still contains about 40 volts, which is plenty to throw a nasty spark.

Hold the camera with the back facing you, as if about to snap a picture. The right side is a compartment that holds the take up spool. If the photofinisher hasn't already pried the door off the compartment and discarded it, do so. Then grasp the right side of the back and pry that off the rest of the body; it has two latches along the bottom and two along the top. Pull hard enough and the back will open like a door, hinged on the left. Pull the hinge tabs out of their slots and throw the back away. This exposes the feed reel in the left compartment. Throw that away. Pry off the clear plastic top and discard; there is one latch in the back and three in the front. Molded extensions of the clear plastic top also reach down and hook into gears and springs. You might need to pry with a screwdriver. Little gears may go flying into space; protect your eyes.

Turn the camera around so that it is facing you, as if to take your picture. You want to remove the plastic piece that covers the front. Examine the left edge and you will see a space between the front cover and the front of the chassis. Pry apart at that point and it will snap, lifting up a little. Keep tugging and it should snap again, the whole front coming off in your hand. Throw it away, along with any loose parts that fall or shoot out.

The right one third of the camera contains the flash circuitry on a board that is roughly rectangular, with an extra finger extending towards the left. Now we have to get it out without getting electrocuted.

The shutter assembly is halfway down the front of the body and about one third in from the left. It has two red trigger wires going from metal contact strips over to the flash circuit board. Using insulated diagonal cutters, cut the trigger wires from the shutter contacts, leaving the wires that attach to the circuit board.

Locate the latches that hold the flash circuit board to the body and cut them off; there is one on the left finger of board that extends towards the shutter and another on the top right corner. Then turn the camera over on a soft insulated surface, letting the board fall out. Dispose of the body and any leftover parts. The circuit board and attached electrical components are all that you want to keep.

This diagram shows what the board should look like.

Take a resistor, anywhere from 3K to 15K and 2W or better. Use two pairs of insulated clip leads to put the resistor in parallel across the large energy storage capacitor. This will dissipate the remaining charge in the capacitor. Measure the voltage across the capacitor. When it hits zero, which should only take a few seconds, you can take off the rubber gloves.