Final LED tests

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.

Transistor issue

As discussed in our previous LED testing post , we tested the ASMG-PT00 and the results were fine. A few days later, we tested the LE RTDUW with the same transistors and were surprised to see very little difference in intensity. It turned out the transistor we were using (ULN 2803A) was not suited for lighting the LEDs for such a small amount of time (100µs).
Luckily, Alexis ordered better transistors, NPN this time, and so we set out to test all the LEDs again, including the SMD PLLC2 ones.
The transitors we used for the tests were the FZT600, the PBSS4480X, and the ZXTN25012EFL. They all gave good results, so we decided to keep the smallest of the three (the ZXTN25012EFL) for our PCBs.

The circuit we used for the tests.
R2 = 65 Ohms, R1 = (VCC – LED_VOLTAGE) / LED_CURRENT

The SMD PLLC2 LEDs

Out of the four SMD PLLC2 LEDs we considered, the ASMB-BTE1-0B332 had the brightest intensity so we discarded the other three.
The luminosity we got by overdring the LED at 100mA was fine for small petals, but the lumonisty drop was too high when using waveguides so we definitely dropped our old idea using waveguides , and our idea to use waveguides for the top PCB.
Since space is not so critical on the top PCB, we decided at that point it would be fine to use the bigger ASMG-PT00 on the top PCB. We also considered adding additional small ASMB-BTE1 LEDs on the top PCB to light even more petals at the center, but it added too much complexity to drive them, and didn’t seem worth it.

ASMG-PT00 vs LE RTDUW

By using the NPN transistors Alexis gave us, we were able to exploit the full capacity of the big LE RTDUW LEDs and noticed it indeed gave a much brighter intensity.
They did however require 1.4 A, which meant we would have to supply a ridiculously high 260A peak current (albeit only for 200µs)… They were also quite big, and we were not sure it was possible to fit them on the PCB petals.
For a while, we discarded the LE RTDUW for these reasons, but then Alexis told us he managed to fit them on the PCB petals, and he suggested we try underdriving them at 200mA.
After testing it turned out the LE RTDUW still gives better intensity than the ASMG-PT00 when being driven at 200mA, which meant at this point we had all the reasons to use the LE RTDUW.

Conclusion

We will use:

  • 62 LE RTDUW LEDs for the PCB petals : they can work fine at 200mA, and we will have the possibility of making them even brighter if our final architecture enables us to supply more current
  • 16 ASMG-PT00 LEDs for the top PCB
  • 1 LE RTDUW LED for the top PCB to light the top center of the sculpture

By using these two powerful LEDs, our phyllo should still give a nice result in a luminous room, and a great result in a dark room.

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