Today, my partner and I worked on leds for migB. We had to find a way to connect properly about a hundred of leds. The precise number is not defined yet. As we say, sleep on it. I hope we’ll have clearer ideas about that tomorrow. Two challenges here : get the leds controlled by the micro-controller and find an intelligent way to allocate them on the sphere.
The first one was quite easy (Thank you Alexis ! ). We are very likely going to use RGB led strips. These devices are really amazing. You may cut them, extend them by soldering and you control them with at most 2 wires. It facilitates our implementation. There will be less wires inside the balls, less solder and less pins used on the micro-controller. No need to use a driver either. So, is everything perfect now ? Not perfect, but it could have been worse. Actually, we can’t use multiplexing with these strips. Except with the DotStar series from Adafruit, but we don’t have precise values yet. RGB led strips act like shift registers. You push the configuration of the farthest led, then the configuration of the previous one, of the previous one and so on. The longer your strip is, the lower the refresh rate is. This model permits to keep the configuration even if the bus is disconnected. Unfortunately, as there is no multiplexing, all leds are powered on all the time (with a PWM modulation, but you get the idea). Therefore the consumption can be quite high. 7A @ 5V with the 144 leds NeoPixel strip from Adafruit ! This consumption is obtained when all leds are white and the brightness is maximal. As we will probably never meet this configuration, the battery is going to last more than 1 hour. With less leds used simultaneously and a reduced brightness, we will limit the consumption.
The allocation of the leds on the sphere is not easy. We would like to have and homogeneous distribution and aligned leds. That’s impossible. We found a led ball made of PCBs (and a video). Here, the alignment is privileged. It is good to display images or symbols, but the poles are in darkness. Not funny. It is difficult to find a projection which keeps the aligment. We have to make more tests.
To be continued…