Chiptec Loja Informática. Projects » Blog Archive » Build a Portable Screen. I do a lot of projection installations, in unique locations, usually with about zero setup time. When I looked into buying a professional 10’x7’ “fast-fold” screen, I was blown away by how much they cost. Instead, I decided to design my own, using easy to find materials. The Challenge: 1. Fast to set-up 2. Fits in a cab 3. Front or rear projection 4. Affordable Tools: Sewing machine Scissors Pipe cutter ($20 most hardware stores) Materials: Aluminum Electrical Conduit ($11 for 10’ pole) 4 Aluminum Elbow Joints (”Speed-Rail” brand, 1” dia. roughly $10 each) Front Projection Material (Dazian in NJ, $110 for 9’x7’)OR Rear Projection Material (Dazian again, $170 for 9’x7’) Lycra Fabric (strong, not thin stuff), stretches in both directions (most fabric stores, $16 for 3 yards) Instructions: 1. 2. 3. 4. 5.Wheel the sewing machine along this seam, with a very wide zig-zag stitch. 6.
That’s it! To make the screen cab-ready, the poles have to be cut down to 5’ lengths. MAKE: Blog: Synchronizing fireflies. Robot Room: Color Sensor from a Reversed LED and Op Amp. One of the first lessons that an electronics student learns is that an LED provides light from current flow. But, did you know that an LED put in backwards provides current flow from light?
Yes! It’s true. Don’t believe me? A multimeter in voltage measurement mode detects voltage in a discrete LED when held close to a light source. Hook up a high-quality ultra-bright red LED by itself (no battery or other circuitry) to a multimeter in voltage measurement mode. An LED (light emitting diode) is a photosensitive semiconductor with a lens. Photodiodes are used in robots and devices as light sensors. Unfortunately, even under the best conditions, photodiodes (and reversed LEDs) don’t provide a lot of current flow. You can connect a standalone photodiode to the input of a standalone transistor. Putting this all together - a color sensor can be made from a reversed LED and an op amp chip. Example schematic for amplifying a photodiode using an op amp.