[Ben] told us about his POV globe yesterday. We took a look and saw just one photo and the code with no real explanation of his project. He certainly set to work over night and now we see all the goodies we look for in a great build log. He even threw the Hackaday logo up for our enjoyment. His build is well executed and he found some creative ways around the common problems in these projects. We take a closer look after the break.
[Ben's] design looks much like an actual globe, with a base, a frame, and a rotating ring mounted with its axis tilted (just like the earth). 72 surface mount LEDs are used for the display, a PC fan with the blades removed provides the rotation, and a reed switch in conjunction with a magnet is used to sync the rotation with the display parsing.
Surface mount components are meant to be placed and reflowed on a circuit board. They are usually considered too small for free-form circuits. [Ben] made this process work for him by lining up all 72 LEDs face down on the sticky side of some masking tape. This made it much easier for him to solder together the multiplex needed to interface them with the microcontroller. You can see he is using varnished wire that can be soldered directly without the need for stripping. [Ben's] using a slice of a clear DVD-R container cover as the rotating ring for the display. On the right side of the picture above you can see the completed LED multiplex installed in this transparent ring.
Getting power to the rotating part of a POV display is always an issue to consider. [Ben] tried feeding the connection through a brush motor but had problems with power loss. His next attempt involves using a headphone jack and connector as the pivot point. Regulated power and ground are passed through two of the connections and he’s had great success with this system. Above, you can see the connector before it is fully inserted in the jack on the protoboard.
A reed switch is glued to the transparent ring and is actuated when it passes a bar magnet on the frame. This allows the microcontroller to measure the rotation of the ring, and sync the display output.
[Ben's] done a great job here. He salvaged a lot of the parts, including the LEDs. He’s chosen an Atmel AVR ATmega8 for the microcontroller. This is an inexpensive and readily available chip that is pin compatible with the more powerful ATmega168 so there is a possibility of future upgrade if animations or other functionality are desired, requiring more programming space. We would suggest a decoupling capacitor on the power pins of the uC in order to help filter out any noise on the lines, especially considering the rotating connection used to provide the regulated power.
WE WANT ONE!