LED’s do some tests

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. Vlaya previously 3D-printed a few different-sized petals to test how well the LEDs manage to light them.

3D-printed petals in various sizes

So the first thing I had to do was find a way to generate the needed control signals. To that end, I adapted a previous ChibiOS project on an STM32-E407 Olimex Board to quickly generate the required PWM on GPIO pins.

Since the LEDs require too much power, they cannot be driven directly by the GPIO pins. So we’ll use transistors to drive the LEDs with an external power supply. For the test itself I used a ULN 2803A Darlington transistor array.

Circuit schematic for one LED (Red or Green or Blue)

But first, the LEDs had to be soldered onto mounts for ease of use :

LE RTDUW S2WP (on the left) and ASMG-PT00-00001 (on the right)

It turns out the transistors in the ULN can deliver at most 500 mA, while the LE RTDUW S2WP, which is among the most powerful SMD LEDs we found, requires 1.4 A. On top of that, we didn’t have adapted resistors on hand. So I ended up only testing ASMG-PT00-00001 yesterday. We’ll test the other LED on Monday, although this one already seems to be bright enough for our needs.

Here are some pictures, taken in the dark and under bright lights :

The white balance was a bit off …

Since we plan for the Phyllo to be used mostly in the dark, this seems like it will be bright enough 🙂 . But we’ll still try the other LED on Monday. We’ll keep you posted !

One Reply to “LED’s do some tests”

  1. Quoting the datasheet for ULN2803A: “Applications requiring sink currents beyond the capability of a single output may be accommodated by paralleling the outputs.”. If you need more than 500mA per LED, this is one of the options, and that’s what the typical application diagram shows.

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