Sharing the display of your smartphone can be tricky. Wireless HDMI and mirroring are good options, but what if there is no TV screen to receive the signal?
Well, you could turn your phone into a projector.
Yes, you read that right. And all you’ll need is a lens and an old shoebox. For less than $10 you can make a smartphone projector using items you might already have around the house.
Intrigued? Let’s begin!
How a Projector Works
Building a DIY smartphone projector is not an original idea. Luckies’ Smartphone Projector, a cardboard flatpack system that you can build yourself, has been around a few years. This is basically a DIY version of that.
Essentially, the device is a camera obscura—a black box with a hole in it and illuminated image within.
The camera obscura is one of the keystones of photography. An image can be projected through a small hole in a box or even room, and displayed on the opposite side, rotated 180 degrees. Without the discovery of this optical phenomenon, it is unlikely that photography and the photographic camera would have been developed.
Projectors use this principle, using a lens to rotate the image, hence righting the image so it can be viewed. The same is true for a cinematic projector, a home theater LCD projector, and any smartphone projector that you buy.
But as these devices are basically a box with a lens, they’re easy enough to build at home. Let’s find out how to build a shoebox projector to use with an iPhone or Android smartphone.
Step 0: Things You Will Need for Your Phone Projector
To make an iPhone (or any smartphone) projector you will need:
Two boxes, one slightly smaller than the other. A lens. This might be a magnifying glass or other biconvex lens—perhaps from another projector. A method of positioning and securing your phone. Black (or dark) duct tape or matte black paint and brush Pencil. Craft knife or similar cutting tool. Suitable cutting surface.
Your boxes might be shoeboxes or perhaps tissue boxes. They should be similarly sized, with one small enough so that it can fit inside.
The sort of lens you will need for this project is a biconvex lens. These can be purchased from photography shops or online from specialist retailers, or even Amazon. They’re often bought as toy magnifying glasses.
Step 1: Get an Idea of the Focal Length of Your Shoebox Projector
To project your smartphone display through the hole in your box, you need to consider the focal length. This is essentially the distance from the phone’s display to the lens.
Find a darkened room and switch your phone’s display to the maximum brightness. Place it on a table, around six inches behind your lens, pointing at a blank wall or pinned-up sheet of paper.
This should give you enough information to judge the size of boxes you will need. The rationale behind using two boxes is simple: you can adjust the focus by moving the lens.
There is another advantage to this. The further the projector is from a surface, the wider the spread of light becomes. This means that big projections will be very dark in anything other than pitch darkness.
Step 2: Install the Lens in Your Shoebox Projector
To add the lens, first place it on the end of the box where you want to mount it and draw around it. Cut the hole with the craft knife, then repeat on the second box, ensuring the openings line up.
Finally, use the duct tape to secure the lens.
Other options are possible. Hot glue, for example, will hold a lens in place, as might adhesive putty.
Step 3: Mount Your Phone in the Projector
With the lights low, it’s time to place your phone in the projector.
You might have chosen a box paring slightly narrower than the phone. In this case, cut a slot through both sides of the box where you plan to place the phone. It should slide into position and remain secure as long as is required.
For wider boxes, find a way to attach your phone’s case to the back wall. This might require hot glue, or tape. You should then be able to simply snap your phone into the projector when you want to use it.
Step 4: Make the Projector Brighter With a Dark Interior
Most boxes are light colored on the inside. This will likely interfere with the quality of the picture, however.
To test this, place your phone in the box with the lock screen disabled and the brightness turned to full. With the lid replaced, turn the lights down and check the quality of the projected image.
You’ll find the image washed out, caused by the light bouncing around the inside of the box. To guide the light through the lens, make the box interiors dark. You might use a black matte paint, or black duct tape.
Neither is a quick solution, but duct tape doesn’t need to dry, so use this to save time. Whatever material you use, completely blacken the interior of your box. You can probably skip the area behind your phone.
Note that the duct tape will add to the interior width of the outer box slightly. While paint is a smarter option here, the tape can add some useful friction to the focusing mechanism.
Step 5: Set up Your Smartphone for Projection
You’re ready to test your build. Switch on your phone, slide it into position, and lower the lights.
Focus the picture and consider the results. You’ll almost certainly notice that the projected image is upside down—like the camera obscura.
How do you deal with this?
Invert Your iPhone’s Display
On iPhone, open:
Settings > General > Accessibility
Tap Touch > AssistiveTouch and set it to On
Now you’ll get a little white dot you can move around the screen. Tap it, choose Device then Rotate Screen and rotate the screen so that it is upside down when you place it in your projector. Finally head over to Settings > Brightness & Wallpaper and turn off Auto-Brightness. With this done, increase the brightness of your screen up to the maximum setting.
Use an App to Invert the Android Display
To rotate your Android’s display, use a third-party app. Several options are available in the Play Store, but they tend to be specific to a specific model of phone.
To find the best option, search Play for your phone plus screen rotate, e.g.: “galaxy s8 screen rotate.”
When you have your screen rotated by 180 degrees, you’ll need to ramp up the brightness. In Android, open Settings > Display > Adaptive brightness and tap the switch to disable. Next, drag the notification area down with two fingers and set the brightness control to full.
Step 6: Put Your Homemade Smartphone Projector Together
With the orientation issue fixed, you’re done. You’re the owner of a smartphone projector, built from boxes, for pennies.
For the best results, project onto a white screen in a completely darkened room. This might be to view Netflix; it could be YouTube. Whatever it is, be aware that the quality will be just good enough, rather than perfect.
You Built a Homemade Projector for iPhone or Android
If you want a cheap projector you can only use at night, then this is the perfect project for you. The images are grainy, and slightly out of focus; it was never going to be perfect. However, there’s a certain amount of charm to it, and this smartphone projector makes an ideal science project.
Note that you don’t have to use two boxes, either. A single box will work, although you will need to spend more time positioning the phone. A lens from an old projector may work better here, secured with adhesive putty in the hole, ready to adjust the focus.
Like being able to project from your phone using a shoebox? Maybe it’s time to use a real projector. These budget projectors are ideal for smartphones .
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