POVLED
A globe-shaped LED display that uses an LED strip spinning fast enough to cause Persistence-of-Vision!
Recycled Design
The main frame was found on the shelf of my dorm hall at MIT - Putz. The original design was definitely for a Persistence-of-Vision globe, which made the construction a lot easier, since I didn’t have to design a frame from the ground up.
It featured Addressable DotStar LED Strips, which use two pins (Clock and Data) to allow for much higher PWM rates when displaying colors, which makes it appear smoother than the normal Neopixel (WS2812B) LED strips when doing persistence-of-vision. It also had a 24V Brushed motor with a belt drive to actually rotate the ring, along with an infrared sensor to detect when the ring is in starting position.
Upgraded Design
In order to mitigate slippage caused by the belt jumping during acceleration and allow for feedback control of the speed/position of the ring, I opted to do direct drive instead of belt drive. I used my 190 kV Longboard motor (certified overkill) with a 12V battery to spin the ring, which meant I had to replace the 80/20 structure holding the ring to make room for the motor mount.
I added new Dotstar LEDs on both sides controlled with an ESP-32 Microcontroller with a digital hall-effect sensor to detect when the ring is at the start of a rotation using a magnet. I also made a custom 16.8V (4S) battery that is built into the frame to power the LEDs using two buck converters to drop it down to 5V.
Custom Battery Pack
I designed and soldered a custom 4S Lithium Ion Battery pack to power the LEDs. I had to make it in two sections that are strapped to the opposite side of the frame to make sure that the whole structure is balanced. On the topic of balance, I also added balance leads to the charger so I could recharge it easily using my lithium ion battery charger.
Big Spin!
Note that it is very difficult to capture the persistence-of-vision effect on camera due to aliasing that occurs at the camera’s 60 FPS refresh rate. Point is, it looks even better in person.
