We started looking into how to implement the SPI communication between the main board and the processor PCBs with Sibille, Xavier and me.
Et each turn of the motor, we need to light up all the 78 RGB LEDs during around 100us at the same time. The motor can spin from 11 RPS to 30 RPS. We have 3 SPI buses leaving the main board, and each SPI bus gets split into at most 5 processor PCB (the top PCB can be counted as processor PCB), and each processor PCB has at most 24 colored LEDs.
Every SPI frame has 16 bits, and we decided to use the first 3 bits as PCB processor addresses, the following 5 bits as colored LED addresses, and the last 8 bits to encode a color.… Read more
Since we started doing research on which LEDs to choose for our project, there three different LEDs / type of LEDs we considered:
- The LE RTDUW S2WP , requiring 1.4 A
- The ASMG-PT00-00001, requiring 200mA
- Four similar SMD PLCC 2 (the package compatible with the flexible waveguides we were considering) LEDs: ASMB-MTB1-0A3A2, HSMA-A431-Z50M1, CLM2D-GCC-CC0F0783 and ASMB-BTE1-0B332, all requiring around 20mA
The LEDs for the PCB petals (see our latest architecture post) were to be either the LE RTDUW or the ASMG-PT00, and the LEDs for the top PCB were to be the ASMG-PT00 or one of the four SMD PLCC2 LEDs.… Read more
Yesterday I set out to test the LEDs we received : ASMG-PT00-00001 and LE RTDUW S2WP. The first is a powerful RGB LED, while the second is an even more powerful RGBW LED. They need to be quite powerful because in order to avoid a blurry image due to the motor rotation the duration of the flashes must very brief, and since the LEDs are flashed only once every 137.5 degrees of rotation that means they are off most of the time.
The goal here is to test under conditions similar to those the LEDs will actually be used in : once every 1/30 seconds, they will be turned on for 100µs using high frequency PWM modulation for the colors, and then switched off again.… Read more
We decided to use the TLC5957 LED driver of Texas Instruments with Broadcom RGB LEDs: ASMB-KTF0-0A306.
First, we have to determine the maximum current which will be used. The 3 colours of the RGB LEDs can get a 20 mA input current max and the driver can handle 20mA sink current max. So we choose a maximum current of 20mA.
We decided to configure the driver with the maximum value for the Brightness Control (BC) (and by consequence, the maximum gain) to provide the intensity to go over 20mA. So we have to choose a value of BC equals to 7.… Read more
Although our initial plan to light the petals was to put waveguides between the petals and LEDs placed on a flat rigid PCB (see “About LEDs“), Alexis recently told us using flexible PCBs might be possible.
Flexible PCBs could be placed directly on the inside of the demi-sphere of the sculpture, thus avoiding the use of waveguides and ensuring a good luminosity. Their drawbacks however includes a high cost and the fact that Alexis hasn’t yet used them for previous projects.
Using flexible PCBs, our idea would be to take advantage of the symmetry of the sculpture and place identical PCBs along each of the 13 spirals.… Read more
Our original idea was to place LEDs on the inner sphere of the sculpture, either with flex PCB, or by drilling the sphere, placing the LED in the holes and connecting them with wires to a rotating PCB contained into the sphere. To facilitate the positioning of the LEDs, we could have modified the design so that we can pin the petals one by one on the inner sphere rather than print everything in one block.
But these designs are not easily achievable. First, Alexis does not know how to design flex PCBs. Second, to have a satisfactory visual impression, we would like to have at least 100 petals.… Read more