The first ever item that we tore down in HackSpace magazine was a dancing Christmas tree and, as we write this latest edition, our minds wander to the festive season, which is only weeks away. In recent years, homes around the world have prepared for Christmas in even more outlandish ways – and surely the most brash and unashamed manner is to project Christmas all over your home using an outdoor projector. But, how do they work, and what can we do with one? Well, there is only one way to find out: we need to take one apart!
Pull it to pieces
The projector is made of a workable plastic, and comes in a series of sections. For example, the lens section is held on with four large cross-head screws. When removing the lens section, we discovered that the lens is real glass, and that the lens is secured over the projection plate with a water-resistant cover, helping to restrict water ingress. Where the power lead comes into the projector, we see a gland that covers the hole for the wire, and protects the unit from water. There’s no rubber seal however, so be careful!
The unit is held together using a mixture of hex screws and cross-head screws. The hex screws are used to cover an access slot where we can insert ‘cartridges’ containing the images to project. Inside the projector, there are multiple cross-head screws, of different sizes. The smallest hold a blanking plate over the LED lenses, to prevent light leakage. The thickest are those that hold the motor and LED PCB to the projector chassis. Just be careful with these screws, as they are really close to the power wires for the motor!
The images projected are made possible using a selection of cartridge slides that contain four images based on seasons/events or celebrations. These cartridges measure 65 mm by 45 mm, by 3 mm thick, and are made of the same plastic as the projector. They can be carefully taken apart to find inside two small lengths of plastic film, with the images printed upon them. Why is this important? Well, using a good-quality printer and some OHP (overhead projector, remember those from school?) transparency sheets, we can print our own images! Trial and error will be required, but the cost of the sheets is negligible.
In the box we find a 12 V 300 mA mains power supply, which provides 3.6 W of power, slightly less than the rated 4 W, but enough. The power supply connects to the projector via a 4.8 metre power cable, and it uses a screw thread and polarised connector to ensure correct polarity and for a secure connection. This also provides some water resistance as it is rated IP44 (typical for bathroom electronics that might get sprayed), but do not rely on this rating for outdoor use. Ensure that the plug is connected to the mains via a fully rated and waterproof outdoor connection.
Sadly, we can’t run the projector from a USB 5 V supply, as there’s not enough power. But if we use a 5 V to 12 V step-up voltage transformer, typically USB to DC barrel jack, then we can power the unit from a USB battery for ultimate portability! The USB output will need to be over 2 A, with 2.4 A being the sweet spot. Typically, these step-up transformers can supply up to 12 V 800 mA, over double the requirements of our projector! If you ‘roll your own’ power supply, do ensure that it is safe and it exceeds the current demands of the projector.
Shine the light
Projectors are extremely simple devices; light is shone through the object that you wish to see, in this case the images from the cartridges. This is then shone through the lens, magnified, and finally projected onto the wall. This means that they have very few electronics inside of them. There are many more projector technologies, and some of the latest use lasers! Yup, we can now fire lasers at our home. These projectors are not like the one which we tore down; rather, the lasers project the shapes using wireframe.
You can also find cheap HDMI projectors – typically restricted to around 800×480 resolution, but they will scale down a 1080p signal – for around $70 on Amazon. These projectors also use LEDs to project the video/image. Because of their low power they need almost total darkness to work, but they’re cheap, and easy to modify, so we’re sure that someone out there can hack them into a useful project!
At the lens end of the projector we have a small fan that is there to keep the unit cool, but is nowhere near the LEDs that project the light. As for the LEDs, we have four 1 W LEDs, commonly used in torches (aka flashlights for our American readers). These LEDs are focused through a thick lens, and this gives us the best beam of light possible for the projector. To rotate the inner lens used to magnify the projected images, we see a low-speed, high-torque DC motor. The motor and LEDs are directly connected to the power, and there are no other electronics in place to control the projector. But, for those of us with the equipment, we could easily sneak in a Raspberry Pi, Arduino, or ESP32, and the appropriate buck converter (LM2596 to drop 12 V to 5 V for the boards) and motor controller (L298N would be ideal), so that we can control the projector using a web interface or sensor to trigger the projector to life!
This is a simple, fun projector. It has very few electronics, but plenty of space for us to add to it. The unit is water-resistant, but not for use in downpours, as the seal will ultimately fail. The cartridges are easy to open, and grant us the ability to make our own images, meaning we can truly make this our own! For £20, the ‘4 W’ projector is a bargain, while for £30, the 6 W version will produce a brighter and clearer image while retaining the ‘hackability’ of the unit we tore down