DIY Hot-shoe Triggered Off Camera Flash, Out of a Disposable Film Camera

Off camera flashes give you a lot more control over the direction of lighting as compared to a standard on camera flash. With off camera flashes, you may completely do away with natural or ambient lighting and still get descent shadows and depth in your image (in contrast with the harsh shadows and flat looking photos when using the on camera flash). Interesting results can be achieved using a flash off the camera, even with the cheapest cameras.

The cheapest flashes start from about about 40USD which is quite affordable to most, but a DIY flash in comparison, costs almost nothing, provided you have an old disposable film camera lying around which you no longer use. So, if you need a dirt cheap off camera flash, either as your first off camera flash or to add to your existing array of flashes in your DIY home studio, it is a great idea to try out this project. This project is very simple, even if your electronics knowledge is somewhat sketchy, you will be able to do it.

What you will need:

A disposable film camera. If you do not have one, ask your friends or neighbors, someone might have it and you will likely get it for free, no one uses it anyway.
Breadboard. (1.5USD)
MOC 3021. (0.3USD)
Two 100 ohm resistors 1/4 Watt. (about 0.03USD each)
Some connecting wires.
A 1.5v AA or AAA cell for the trigger circuit.
Batteries for the disposable camera.
And of course, your digital camera, which should have a hot-shoe mount. If your digital camera does not have a hot-shoe, stay tuned, a DIY project that will trigger this DIY flash with on-camera flash (optical slave function) is coming soon.

Some Tools:

Voltmeter. No one uses a dedicated voltmeter these days, you can use a digital multi-meter which has a voltmeter as one of its many features. If you have a multi-meter, well and good. Else, you can borrow it from any of your friends, or check if a local hobby shop rents out a multi-meter. If you are not sure how to use a multi-meter, please watch some YouTube videos or read some guides before using one.
Soldering Iron and some solder wire.
Adhesive tape.
Screw driver to open the disposable camera.

Step 1: Modifying the Disposable Camera.

Insert a set of charged batteries into the disposable camera and test the flash. After you test the flash a couple of times, let the flash charge and take out the batteries once the flash ready light is on. Note that you do not turn off the flash while removing the batteries. Then trigger the camera without the batteries and let the flash fire. This is to discharge the flash capacitor. Turn off the flash.

Now, take off the front cover of the camera by removing the screws holding it in place. Once you take out the front cover, all the internal mechanisms will be exposed. You have to look for two contacts that trigger the flash. This is entirely dependent on your camera model, but in most cameras, it is placed close to the shutter mechanism, where the shutter when fully open, hits the contacts and forces one contact to touch the other, triggering the flash. Once you find these contacts, confirm it by reinserting the batteries and firing the flash using a screw driver(with a well insulated grip) to short the contacts. Warning: Do not touch these contacts or any other part of the camera circuitry with bare hands. When the flash capacitor is charged, the voltage across these contacts can be as high as 400 V DC. On the camera I used, it was 260 V DC at maximum. After you are done testing, discharge the capacitor once again by following the discharging procedure mentioned above.

Once you have found and verified the contacts that trigger the flash, take a pair of wires and solder each wire to each of the contacts. You may as well stick some insulation tape to ensure that the contacts do not touch and trigger the flash accidentally. You will now have to rout these wires out of the camera body. This can be done as per your preference. I have removed the lens and the shutter mechanism and routed the wires through to the back of the camera and out through a slit cut in the film door. Then, the front cover of the camera can be put back on.

That is it. The modification of the disposable camera is done, now lets test it. Insert the batteries, switch on the flash, let it charge for a couple of seconds, and once the flash ready light comes on, touch the two free ends of the wire to trigger the flash. Remember, the free ends of these trigger wires coming out of the camera are at a high voltage, same as the trigger contacts (I have already mentioned this), do not touch them with bare hands when the flash is ready to fire.

Use multi-meter to check the voltage across the trigger wires when the flash is charged. Do not forget to select the correct range on the multi-meter, the voltage being measured will be around 200-400V DC. Mark the positive and negative terminals, we need this in the next step. Twist both the free ends of wires onto two pins, the pins will help to easily insert the wires into the breadboard. I have not soldered the wires to the pins, you may choose to solder them. Tape the upper part of the pins to prevent accidental shorting.

Step 2: Constructing the Trigger Circuit.

All the electronics components used in this project are easily available at most electronics repair or hobby stores. MOC3021 is a triac opto-isolator used to isolate and protect the hot-shoe of your digital camera, which can safely take a voltage of only up to 6V DC (on most cameras) from the high voltage of the flash, which can be as high as 400V DC. BT136 is a triac which is triggered by the MOC3021 opto-isolator. I have used BT136 triac as it is easily available as compared to SCR which is usually recommended to control a DC source. A triac is meant for AC and can conduct in both directions, however, the resistance to current in the reverse direction is slightly higher, hence the connection showed in the diagram is the forward direction (I am not sure if it makes any significant difference though).

I believe the connections diagram is self explanatory and easy to understand. If you know how to use a breadboard, you are good to go. The orientation of the MOC3021 and BT136 should be as shown in the diagram. If you are not sure of the orientation of MOC3021 IC, the notched side should be to your left hand side and the letters/numbers on the IC should be upright.

Now that you have made all the connections, test the flash by touching the two wires that go to the camera hot-shoe. Do this couple of times to ensure that it fires consistently. If not, check the connections. Electronic components are delicate and may fail if you mess up with the connections. Check the voltage across the wires to be connected to the hot-shoe, it must be close to or less than 1.5 V DC.

Step 3: Make a Hot-shoe Adapter.

Cut out a 18mmX18mm square piece of a 2mm thick non-conductive material. Use any material of your choice, as long as it does not conduct electricity. Mark the center point of the square face, and pierce a metal pin through this point. I have used a high density foam sheet, as it is soft so that a pin can be easily pierced through, yet hard enough to prevent the pin from loosening with repeated use.

Twist the wire coming off the positive terminal (colored red in the circuit diagram) of the 1.5V AA cell onto the pin. Cover the joint with adhesive tape, and cut off the excess pointed side of the pin. Put some more adhesive tape over the cut pin. Now, take the other wire coming off the breadboard (colored blue in the circuit diagram) and stick it right next to the positive wire as shown in the illustration images. Then curl the strands so that the strands reach the underside of the rectangular piece, and make contact with the hot-shoe's base plate(ground).

Check that the center pin has positive and the other wire has negative polarity using multi-meter (this is very important, reverse polarity might damage the hot-shoe). Now insert the DIY hot-shoe connector into your camera's hot-shoe, the head of the pin should touch the central contact of the hot shoe, and the other wire should touch the base plate. Enable external flash on the camera if necessary, and take a photograph to test the flash. The flash should fire when you press the shutter button.

Step 4: Packing, Tips for Use.

A breadboard is meant for prototyping and testing circuits, and it is not a great idea to hook it permanently to your DIY project. If you have access to circuit board printing, you should probably go ahead and print one or use a prototyping board if you want your DIY project to last long and be compact for better portability. But if you do not care about portability and reliability, like me, then just put some adhesive tape on all the connections on the breadboard to prevent the wires from coming loose, and enclose the trigger circuit in a small box. When you enclose the breadboard in a box, better to stick it to the side of the box so that it does not flop around, loosening the connections.

Tips:

Although this DIY flash is a great tool for what it costs, it is by no means a replacement for the flashes sold by photography equipment manufacturers, as it lacks power and duration control, and is not as powerful.
Power and illumination can be controlled by varying the distance of the subject from the flash and the angle of incidence(which might also affect the shadows). For beginners, this will help to understand lighting better.
Use front curtain sync and avoid using shutter speed above 1/250. I could go up to 1/320 on my camera without the shadow of the second curtain appearing in the image.
Your camera's auto exposure will not give you the correct exposure when using this DIY flash. To get a correct exposure, you have to take some test shots and set the exposure manually.