Android & Arduino Controlled Projector Screen
This is my first time using Arduino, or any microcontroller. I’m glad it worked out so well but my wife may not be, due to the stacks of microcontrollers that will being showing up on our doorstep soon for future projects. Any feedback or questions are welcome, as are votes in the Arduino Contest.
I love watching sports, my family loves watching sports, and we all love cheering on our local college team (Go Dawgs). This leads to lots of watch parties on game day. Since there are usually upwards of 15 people we use a projector so everyone has a good view. The downside is the screen. In the past this was just a white sheet tacked to the wall. This was decent but left a lot to be desired.
A motorized, Android and Arduino controlled, Bluetooth enabled, screen. The screen itself is made of white blackout material, giving a smooth bright projection surface. The whole unit is stored above a drop ceiling which the screen is deployed through, into the room (if you don’t have a drop ceiling where you use your projector don’t worry, you can just mount to the ceiling or wall).
New Screen Pros
- Storage – With a push of a phone button the screen is stored out of sight, in the ceiling.
- Setup – With a push of a different button the screen is deployed and ready for use. No more thumbtack holes in the wall or ironing a sheet that was folded up and creased.
- Picture Quality – The blackout material screen does not allow projected images to show through to the back or let ambient light from behind seep through. Also no more having to iron your sheet/screen before use or waves and wrinkles in the screen.
- Wow Factor – Because it’s awesome, enough said.
- Cost – A similarly sized, motorized screen will run you $300, or up to $1500 for a in-ceiling model!
New Screen Cons
- Cost – A white sheet from Wal-Mart is probably a few bucks, where as an Arduino UNO alone is close to $30.
Now that we know why we’re here, lets get cracking!
Step 1: Materials and Tools
- Arduino UNO- $27, Amazon – I used an UNO because this is my first Arduino project and figured it would be best to start with the base model. You probably can use other microcontrollers, feel free to use your favorite.
- Arduino Motor Control Shield – $10, eBay – I went for simplicity over cost and just bought a pre-built, albeit off-brand, motor controller. Mine is based around the L293D chip.
- High Torque Gearbox DC Motor – $10, eBay – You can calculate an approximate torque requirement, formulas and calculation walkthroughs on the next page. Make sure voltage and current requirements don’t exceed what your motor controller can provide.
- 10kOhm, 10 Turn Potentiometer – $10, eBay – Used as a limiting sensor. The pot needs to have more turns than it takes to wrap the screen around the rod. If you are going with a huge screen, or a long drop, you can use a gearbox to reduce the turns on the pot.
- Bluetooth Serial Adapter – $9, eBay – You can use a Sparkfun BlueSMiRF which is easier to use but much more expensive. The off brand ones are also very small which is great for space requirements but can be harder to solder depending on which unit you get. If you can find one with pins and a cable I would recommend it.
- 10 kOhm Resistor – Not needed if you use a BlueSMiRF or other 5 V Bluetooth module.
- 20 kOhm Resistor – Not needed if you use a BlueSMiRF or other 5 V Bluetooth module.
- 2x 9 V Battery – Powers the Arduino and motor. You may need more or less voltage for you motor, scale appropriately or use AC adapters if you have a socket available.
- 2x 9 V Battery Clip/Holder – See above.
- 53″ x 2 Yards White Blackout Material – $7/yrd, Jo-Ann Fabric – This is enough canvas to make an 80″ screen (70″ x 40″, 16:9) with room for the drop down out of the ceiling. If you want a different size screen check out this site.
- 1-3/8″ DIA x 6′ Closet Rod – $10, Lowes – Adjust the length of this piece based on the screen size, width specifically, you select. If you have a different size screen, calculations for determining minimum diameter are on the next page.
- Flange Nut/Panel Nut – Match the the threads to those on your pot. This nut should have ridges in the face to keep it from backing off when tightened (Flange nut only, add a star washer with panel nut.)
- Motor Mount Screws – My motor had two threaded holes in it’s face for mounting. Yours may have more or less and are probably a different size.
- Rubber Grommet – The inner diameter matches, or is slightly smaller than, the diameter of the potentiometer’s shaft.
- 2x Wall Box – One houses the potentiometer, the other holds the motor and Arduino. You are looking for boxes with a flat surface big enough that the rod won’t hit anything with enough space inside for the components.
- Set Screw – Diameter: Should be as large as possible while still fully engaging the motor’s shaft, mine was #10. Length: Longer is better but it must be longer than half the difference between the O.D. of the motor grommet and the motor output shaft O.D.
- Hanger Tape – $2.50, Lowe’s -Used to reinforce my drop ceiling since some of the structure had to be cut.
- Glue/Epoxy/Bonding Agent – Must be able to work on multiple materials.
- Jumper Wires – I got a bunch of Arduino specific jumper wires off of eBay. They are nice because you get the easy soldering and header compatibility of a solid core wire with the flexibility of a multi-strand.
- Scrap Wood – Used to build a structure for holding the whole unit above my drop ceiling.
- Wood Screws, Washers, Misc Hardware
- Arduino Paraphernalia – USB cord, Arduino software
- Android Development Paraphernalia – USB cord for your phone, Android Development Software (for if you know Java), or the MIT/Google App Inventor (What I used, is powerful enough for our use).
- Soldering Equipment – Iron, solder, de-soldering wick/bulb, helping hand.
- Drill & Drill Bits
- Center Punch
- Tape Measure
- Other Basic Tools
Step 2: Calculations
Screen Size Calculations
Use the THIS great website to decide on a screen size. Here are some things to consider when picking a screen size.
- Room size – Check out the viewing distance calculator on the page above.
- Available material size
- Projector abilities
Motor & Rod Calculations
Once you’ve decided on a overall size based on room size, available space, optimal viewing distances, etc. you should run some quick calculations to determine how much minimum torque you will probably need from your motor. The numbers in these calculations are examples, you will need to input your own values.
- Minimum torque required to lift the screen from fully down. Variable = Tm
- Maximum rod diameter. This controls the number of times the screen will warp around the rod. Variable = d
- Material weight. Usually in oz/yrd2 . Variable = w, for this example w=10oz/yrd2
- Gravity, 9.81 m/s2. Variable = g.
- Screen size. Variables = height = H, width = W. For this example H = 53 in, W = 84 in.
- Maximum turns. variable = t. For this example t = 9, which leaves 1/2 turn of the pot on the top and bottom (5% of the total turns top and bottom).
- Find the area, A, of the screen in square yards.
(53 in) / (36 in/yrd) = 1.472 yrd. (84 in ) / (36 in/yrd) = 2.333 yrd. A = 1.472 yrd * 2.333 yrd = 3.434 yrd2
- Find the mass, m, of the material in kg.
(10 oz/yrd2) * (.028 kg/oz) = .28 kg/yrd2. m = (.28 kg/yrd2) * 3.434 yrd2 = .962 kg
- Find the force, Fg, due to gravity and mass, of the screen in newtons.
F=ma=mg. Fg=.962 kg * (9.81 m/s2) = 9.433 N
- Find the diameter, d, necessary for the rod, in cm. C = circumference.
C = H / t = 53 in / 9 turns = 5.889 in * (2.54 cm/in) = 14.958 cm. d >= C/pi = 14.958/3.14 >= 4.761 cm (1.87 in)
- Find the minimum torque, Tm, required to be provided by the motor, in N*cm, assuming the motor acts on the very center of the rod, the weight of the rod has a minimal moment of inertia and mass, and that the screen is hanging from the “9 o’clock”, 90º, position.
Tm = F*(d/2) = 9.433 N * (4.761 cm / 2) = 22.456 N*cm
Now you know exactly what you need in a motor and rod. When trying to find a motor for the most part lower RPMs means higher torque. I found a few motors that were rated 12V, 60 RPM that had a stated torque of 30 N*cm as a point of reference.
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