DIY Projector With Smartphone 📽️

It is a simple, low-resource DIY projector 📽️ that can project the content of a smartphone. You can easily project media such as photos or videos onto a larger surface, which can be useful for collaboration or simply for entertainment. The application is very simple, requiring only a smartphone that can be placed on the surface to display the content. Then all that's missing is the popcorn and so the film night can be started. Have fun with it! 🍿

Some important aspects to consider while working on this project are highlighted using symbols with different meanings, as described below:

ℹ️ = Information / Hint

🔄 = Alternative way

⚠️ = Warning / Pay attention

Materials:

1. Box (Any box is fine, you can reuse your shoebox, old box, etc.)
2. ℹ️ Our size is 220x160x250mm (x,y,z)
3. ℹ️ We generated parts of the box with templates and using a laser cutter
4. Mirror (Example)
5. ℹ️ Should fit inside the box
6. ℹ️ Preferably use a front-surface mirror (reflective surface not behind glass
7. Loupe (Example)
8. Paper (Rather dark paper or (gift) wrapping paper)
9. Can use lighter colored paper and cover it in a black coating.
10. ⚠️ The size needs to be at least 2 times the length + 2 times the width of the box. For the height, it is recommended to at least have 40 cm of bellows. This can either be achieved with a big piece of paper or multiple smaller pieces as described in Step 6.
11. 4 straws
12. Used as a guide, keeping the sticks in place
13. Can use any other mechanism to secure the stick's positions and allow them to move in only one direction
14. 4 sticks (Any stable sticks are fine, i.e. Amazon Edelstrahl Rundstab)
15. The length of the sticks should be around 40 cm. Longer is recommended.
16. ⚠️ The diameter of the sticks has to be smaller than the one of the straws
17. Extra cardboard
18. Used to make some connections of stabilizing parts of the projector.

Tools:

• Pencil
• Ruler & triangle ruler
• Scissors / Cutter
• Glue
• Hot glue gun
• Tape
• Smartphone
• ℹ️ We used iPhone 13 Pro, but any smartphone is good
• ℹ️ The higher the smartphone's display brightness, the better (maybe check out its display specification and look for "nits")

Material-Cost:

~ 5€ - 20€ (Depends on your availability of the materials on hand)

Before you start, be sure that you have everything that is stated in the supplies list. In many cases, there are alternatives you can use or optimize based on your budget and the supplies available. Most of them are highlighted during the process using the icons explained above (🔄).

⚠️ It is recommended to use something to cover your canvas to prevent any damage that could be dealt with while cutting, gluing, and drawing lines during the process of making.

The purpose of the loupe here is to spread the image of the smartphone and project it on a larger canvas. ⚠️ For this reason, it is recommended to use a loupe with a large lens. Since, the bigger the lens, the more light can be bundled and projected onto the canvas. ⚠️ However, keep in mind that the magnification factor also plays an important role. A rule of thumb says that the focal length of the lens should at least be as big as the smartphone screen diagonal.

• ℹ️ A bigger focal length is recommended.
• ℹ️ Usually, the focal length is hard to find for loupes. For this reason, this short formula can help you to determine it.

M ... Magnification factor

f ... focal length [mm]

M = 250 [mm] / f

Using this formula, you can calculate your loupe's focal length. In our case, this would look something like this:

M = 1,75 times

→ f = 250 / 1,75 = 143 mm

Our screen diagonal is a bit bigger than that (155mm). However, since the screen has a notch and crops video content, it is not much of a problem.

You can also find a simple calculator for this purpose here.

ℹ️ Your box's size doesn't have to correspond to our box's size (220x160x250mm). However, need to make sure that the mirror you use fits inside your box.

1. Make sure your box is rigid enough. A basic shoebox or cardboard box should do just fine. However, keep in mind that the box needs to hold the mirror in place. Any bending of the box might cause issues while keeping the mirror in place.
2. (Optional) You can wrap your box in some wrapping paper, or color it in a color of your choosing, so it looks better in the end. In our case, we simply wrapped the box with some tape, to give it a unique and cleaner look.
3. Find the diameter of your loupe. Often the size of the lens is noted somewhere on the loupe or can be found while checking its description. In case it is unknown, you are able to measure it simply using a ruler.
4. Mark the hole for the loupe on the box. Find the center of the sidewall where you want to place your loupe and mark it. Using the triangle ruler, add markings for the diameter of your loupe. Try placing the loupe on the markings and ensure you have done them correctly. If they fit and the loupe is placed in the center, hold it in place and trace its outline.
5. Cut out the loupe hole. ⚠️ Either you use a sharp cutting knife (be careful!) and cut out exactly the outline of the loupe, or you can also use a pair of scissors to do so. ℹ️ In the case you use scissors, it is recommended to poke a hole in the middle and start cutting towards the outline, starting in the center. Otherwise, one might easily get off the outline and cut away too much.
6. Place loupe inside the hole. For testing purposes, you can simply attach the loupe on the box using some tape. This is also helpful if you want to reuse the loupe again for other purposes.
7. 🔄 You can also remove the lens from the loupe's frame and permanently attach it to the box. ⚠️ While cutting off the frame, make sure you are not scratching the lens. Otherwise, the projection quality will suffer in the end.
8. Afterwards, you can attach the lens, using some hot glue, for example. ⚠️ However, make sure that the lens is not tilted in any direction. This also might otherwise cause some loss of projection quality.

🔄 If you do not have a cardboard box of a similar size at hand, though you have some larger pieces of cardboard lying around, you can also use the image attached to draw the outlines for a "stick together" box. This can also be used with a laser cutter to, for example, cut out a box from pieces of chipboard (wood). It is also possible to use your own dimensions and styles to do such a box. Therefore, boxes.py can be recommended.

To make sure, the height of the projector is variable (necessary to adapt focus). We use a construction with rods that are guided using straws. Therefore, we conduct the following steps:

1. Poke holes in each corner of the box's bottom. Here, it is important that the holes have a diameter equal to the rods.
2. Attach straws to each corner of the box. The straws need to match the poked holes. Then they can be secured using some glue. In our case, hot glue was used.
3. Make sure that the rods slide through the poked holes and straws.

The mirror's purpose is to reflect the image of the smartphone and mirror the orientation. Otherwise, it would result in text being projected backwards, making it hard to read. For this reason, the mirror is placed inside the box at a 45-degree angle to reflect the image of the smartphone and project it through the lens.

1. Make sure your mirror fits inside the box at a 45-degree angle. It is not so critical if the height of the box is too small to fit the whole mirror. What is important though is that the mirror has a 45-degree angle and can be placed facing the lens cut out.
2. Create stabilizing pieces to mount the mirror inside the box. Use the extra pieces of cardboard and create feet in the shape of a triangular ruler, that can be attached to the back of the mirror. Here again, it is important that those triangles have a 45-degree angle.
3. Attach cardboard feet to the mirror. Using simple glue, hot glue, or tape you need to attach the feet to one side of the mirror, so it can be placed at an angle inside the box, as tested before. We used simple tape to attach the feet to the mirror. This allows us to take apart the setup without any stains on the backside of the mirror.
4. Place the mirror inside the box. ⚠️ It is important that the mirror is placed in the center of the box. This is necessary, so the smartphone can also be aligned in the center on top of the system. Otherwise, one has to always figure out at which position the smartphone needs to be placed to get the perfect projection. Here again, you can use various techniques to attach the mirror to the box. In our case, we used hot glue on the feet to secure the mirror's position inside the box.

The bellows consist of 8 parts:

• 4 corner pieces
• 2 longer sides (front & back)
• 2 smaller sides (left & right)

You can either use a big piece of paper (e.g. wrapping paper) or multiple smaller ones. If smaller ones are used, you need to consider that they at least need to match the length & width of the box. Also, the folding pattern, provided below, needs to be split up into multiple pieces.

⚠️ When using paper with different colored sides, it is important to keep in mind that the inside of the bellows should be the dark side of the paper.

⚠️ Pay attention while folding to strictly match the lines! Otherwise, this will result in issues when connecting all the pieces together.

ℹ️ It is recommended to place the corners at the outside of the bellows, as it looks much smoother.

🔄 If you want to avoid the folding work, you can just wrap the box without the folding work. However, issues arise if you want to move the top plate.

1. Draw outlines on paper. Using the pattern provided below, you need to make outlines on your paper. ⚠️ It is important that the corner piece's zigzag lines are at a 45-degree angle. Otherwise, this would result in corners that can not be folded to a 90-degree angle, making it much harder to combine all the pieces and have a good folding mechanism.
2. Cut paper into pieces. Using a cutting knife or a pair of scissors again, you need to cut paper into the necessary pieces.
3. Fold bellows.
4. Folding sides. If you have all pieces, it might be easier to start by folding the sides. With a simple alternating fold, you prepare the side pieces for further usage.
5. Folding corners. The corners are a bit more tricky to fold. However, the system is similar. Again, use an alternating fold starting with the zigzag pattern. After the zigzag is prepared, fold the remaining lines similar to the side's pattern.
6. Combine pieces. This part can be a bit tricky!
7. Combine the pieces on part at a time.
8. Make sure that the folding patterns match.
9. Align the pieces and stretch them.
10. Apply glue on the edge of one piece and place the other piece onto it (e.g. corner + glue + side)
11. ⚠️ Make sure that the paper keeps stretched while the glue dries. Otherwise, the fold might stick together. ℹ️ You could use something to weigh down on the glued position to keep your hands free.
12. Repeat the process for all sides & corners until you have the rectangular bellow.
13. Refold bellows. After everything has dried successfully, you want to refold the patterns due to the stretching applied while gluing the parts together.

🔄 Here again, a piece of cardboard can be used. In our case, this piece was laser cut, but this is not necessary

🔄 Any stable rods are fine as they can be made from metal, wood, etc.

1. Find out the screen size of your smartphone display. Either measure it with a ruler or look for the specifications you can find online.
2. Mark holes for the smartphone and rods. The whole of the smartphone needs to be placed in the center. The cutout needs to be as big as the screen size. ⚠️ Keep in mind to keep a little space to place the smartphone on. Otherwise, it might fall inside the projector and potentially break something.
3. Cut out holes. With cardboard, use a cutter knife or a pair of scissors, as mentioned above. In the case, you want to use chipboard and laser cutting, to create a rectangle with a width and length similar to the box's measurements. For the smartphone cutout, use your own measures and create another rectangle in the center of the bigger one.
4. Combine pieces.
5. Place rods in guides. Put the rods inside their guides. Also, make sure they fit through the holes in the top plate.
6. Attach rods to the top plate. Using some hot glue, you now need to attach the rods to the top plate.

1. Add bellows. We put on the bellows and secure them using some glue or tape.
2. Secure rods. To prevent the rods from popping out of their guide, we add a little big of glue at the very end of the rods. ⚠️ Make sure you do not attach them to the box, as they are still needed to change the height of the bellows and box.

🔄 Feel free to upgrade your project by coloring it or decorating it with different materials.

The projector is now completed! Hurray!!

How to use it:

1. Find a flat projection canvas and position the projector facing towards it.
2. Make sure your smartphone is set to maximum brightness and presenting the content you want to consume on the large screen.
3. Place the phone on top of the projector and align it to be exactly at the center.
4. Now change the height of the projector to get a sharp image.
5. ⚠️ Keep in mind that, the closer you are to a canvas, the higher the distance needs to be from the smartphone to the lens (projector at max height). If you are getting further away, the smartphone needs to get closer.
6. ⚠️ The bigger the projection, the darker the image! This is due to the light being spread further apart, making it less bright compared to a more focused and bundled image.

ℹ️ To have a better projection experience, make sure you are in a pitch-black room. Every bit of light radiation from somewhere else could disturb the experience and make it less pleasant.