This LED sculpture attempts to make use of one of San Francisco's unusual, tight street corners to give people something fun to see and play with. As they come around the corner of Market and O'Farrell and Grant Streets, they pass near this big cylinder. When they do, ultrasonic range finders detect them and project randomly-chosen images for them directly in front of them. As they move around the cylinder, the images follow them.
The deadline for exhibiting the piece was October 6, 2016. Unfortunately, the ultrasonic system was not working by then, so the piece operated in less-interactive way - displaying pretty animations of various sorts. Here are photos and videos of the result:
Step 1: The Cylinder
The structure of Follow is a cardboard tube, roughly 43" in diameter and 78" tall. It is a "Sonotube", a commercially-available building product. These are used as forms for pouring concrete pillars. I ordered mine from Level Construction Supply in Oakland.
Next, the cylinder is sawed open, with a single, very careful cut from top to bottom. This was necessary for Follow since it was to be placed around an existing clock tower. You may not need to do this but I found it makes dealing with the electronics a lot easier.
Next, I painted the cylinder black. Then I installed nice little stainless steel draw latches from McMaster.com to bind the cylinder back together.
Step 2: The LEDs
The LED strips are IP65-rated with self-adhesive backing. They have 72 APA102 chips per meter, resulting in a spacing of approximately 0.55". 245 chips fit nearly perfectly around the circumference.
There are 48 strips, resulting in 11,760 pixels/chips.
Step 3: The LED Electronics
There are 6 PixelPusher LED controllers installed just inside the cylinder. The wires for each LED strip reaches inside around the cut cardboard edge and plugs into a PixelPusher.
The PixelPushers are powered by 3 300W/5V Meanwell power supplies.
Each PixelPusher's cat5 jack is connected to a 100-baseT 8-port switch, which is connected to the LAN port on a Xiaomi Mini Wifi router.
Step 4: The Ultrasonic System
30 Maxbotics ultrasonic transponders are installed around the circumference of the cylinder, just below the LEDs. Their analog outputs are connected to the analog inputs of two Arduino Mega microcontrollers. Software on both of these convert the analog voltages to 8-bit digital values and puts them into a 30-byte buffer which is transmitted in a UDP packet 20 times per second. Each packet is encoded in the OSC data format.
Step 5: LED Lab
This iPad/iPhone app controls LED displays of any size and configuration. It drives all of my pieces that those of 1000s of LED artists worldwide. I wrote it.
It controls Follow too, but it also receives those UDP packets from the Ultrasonic System and uses the data to create, move, and delete pictures on the fly. The app has long supported creating the creation of pictures by touching the iPad screen. It wasn't much modification to have it do the same from the UDP data.
You can download this app here: http://appstore.com/ledlab
It's free to try, but if you use it regularly, you'll be prompted to make in-app purchases for the features you need.
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