The Fujifilm Instax Mini 8 camera records images onto photosensitive paper that is ejected immediately after the photograph. This teardown looks at the circuit inside the camera.

The Fujifilm Instax Mini 8 camera allows users to create a photographic print, approximately the size of a business card, in about a minute.

A user begins by pressing a lens-extend and open button. Then a light sensor indicates to the user a particular aperture setting should be used through multiple LEDs that are projected through the viewfinder. The user rotates the aperture setting ring to the indicated position and uses the viewfinder to approximate the image that will be captured.

The shutter release button opens the shutter for a fraction of a second while the flash circuit fires. Photons travel from the flash to the scene and back to the lens of the camera. Those photons travel through the lens and are focused on the photographic film. There, different molecules that are deposited on various layers of transparent film react to photons that traveled through the lens.

Finally, a motor drives a gear system to eject the film to be viewed by the user.

### Taking the Camera Apart

There are multiple thermoplastic screws around the circumference of camera that hold the two sides together. Most come out with ease, but a few will spin without backing out. These can be removed by gently separating the sides of the case while twisting the screws. The shear tension on the bolts provided by the opposite sides of the case allows the threads to engage and the screws to be removed.

Once the case is removed, several more screws are visible that hold the circuit board and various mechanisms and switches in place. Remove them while unthreading the wires that connect to the off-board components.

See the video below to see the teardown of the camera.

### What's Inside?

R5F10377A
1625KN404
Microcontroller$1Datasheet 6704 P4009DC Buck Converter$1Datasheet
Pulse TransformerDatasheet

#### (1)  Xenon Flash (Yellow)

A xenon flash tube (example datasheet) provides light to illuminate the scene by converting electrical energy to light in a just a few microseconds.

Typically, a tungsten anode and cathode are held inside a partially evacuated glass tube filled with a small amount of xenon. When it is time for the flash to fire, a potential difference is quickly established between the anode and cathode at the same time that a pulse transformer connected to a metal plate around the flash tube creates an electric field along the length of the tube. The gas inside the tube ionizes and charges move rapidly through the circuit and across from the cathode to the anode. The electrical energy allows electrons to jump to high energy levels and, as they drop to lower energy levels, photons of light are emitted.

#### (2)  Insulated-Gate Bipolar Transistor (Orange)

##### Pinout diagram of IGBT microchip via ON Semiconductor

The lack of manufacturer logo on the topside markings did not allow me to positively identify the specific IGBT used. However, this datasheet from ON Semiconductor provides the basic information necessary to understand the flash firing circuit.

##### Example IGBT flash fire circuit from ON Semiconductor

Flash firing circuits such as these begin by storing energy in a high-voltage capacitor and then rapidly transferring that energy to a xenon flash tube. IGBTs allow for rapid transient potential differences, with the one shown in the application note capable of $$\frac{400\;V}{1 \mu s}$$. The rapid change in potential difference allows the pulse transformer to create a strong electric field and allows for rapid energy conversion and very bright flashes.

#### (3)  Light Emitter and Sensor (Magenta)

The chemicals in the printer paper must receive the proper amount of light to create an acceptable photograph. Too much light and the picture appears washed out; too little light and the picture is dark. Photographers can control the brightness of a photograph by adjusting three factors: the film sensitivity (referred to as ISO, ASA, or film speed), the exposure time or shutter speed, and the aperture (diameter of the lens).

In this camera, the film is of a single type and the shutter speed is constant and controlled by the mechanisms inside. The only variable is the aperture. Opening the aperture allows more light in and leads to blurrier images. Reducing the aperture diameter allows less light in and results in sharper images.

This emitter pictured above illuminates the area directly in front of the camera with infrared light and the amount of light received is detected and transmitted digitally to the microcontroller. The precise detector cannot be identified without manufacturer markings on the back side of the device, but Silicon Labs and Texas Advanced Optics / AMS make sensors that can do the job. It is impossible to know without identification or probing the circuit but, based on the pinout of the device, I believe this to be a light-to-frequency converter similar to the TSL237T (datasheet).

#### (4)  Microcontroller (Pink)

##### Block diagram of the RL78 MCU from Renesas

The microcontroller is based on the Renesas RL78 CPU core, which features a Complete Instruction Set (CISC), variable clock timing, and four bands of 8 x 8-bit registers as well as all of the typical accoutrements expected of today's microcontrollers: serial interfaces, AD converters, code memory, flash memory, on-chip oscillators, and several dozen I/O ports.

It is connected to the light sensor, the LED indicator lights, the various mechanical switches, and the motor driver.

#### (5)  Transformer (Orange)

The first transformer is used in the flash charger circuit. The direct current provided by the batteries is pulsed by transistors and the current is passed through a thick wire wound a few times around a much thinner wire wound many times around a permeable core.

A pulse of current moves through the thick wire on the outside of the transformer and creates a changing magnetic field. The changing magnetic field induces an electric field in the internal coil. The internal coil has many more windings than the outer coil and the smaller coil has a greater potential difference at a lower current. Over the course of several pulses, enough charges are stored in the capacitor to fire the flash

#### (6)  Transformer (Blue)

This pulse transformer creates a high potential difference on a metal strip that is near the flash tube. This allows the ionization of the xenon gas to occur at a lower potential difference across the anode and cathode of the tube.

### Conclusion

There is a surprising amount of circuitry inside this camera. When it was first recommended for a teardown, I expected to find a flash charging and firing circuit similar to the type found in a disposable camera. I was quite surprised to discover a microcontroller and complex circuitry apparently needed to give users an instant photograph.

Enjoy the fun and instant aspects of these cameras, but make sure you order film with the camera, as none is included in your purchase!

Featured image used courtesy of Fujifilm.

Next Teardown: Ikea Wireless Lamp