APA102s are really bright! Even on the lowest setting (brightness 1 out of 255).

Justin_Shaw · April 30, 2017, 8:07pm

APA102s are really bright! Even on the lowest setting (brightness 1 out of 255). Anyway to make them dim even further? I need a dim setting for an alarm clock.
Thanks!

marmil · April 30, 2017, 8:25pm

Are you currently displaying white? Maybe try just red or a reddish color?

Are you going to diffuse the pixels at all? If so that will cut the amount of light down further, perhaps a lot depending on what you choose.

Justin_Shaw · April 30, 2017, 8:27pm

Thanks @marmil . I will be putting some darker acrylic over the top and can use other colors. Just wondering if I could digitally dim them.

marmil · April 30, 2017, 9:02pm

I don’t think there is a way to go below brightness value of 1. My suggestion would be to darken things with diffusion.

Justin_Shaw · April 30, 2017, 9:09pm

Gotcha. Thanks again.

Louis_Beaudoin · April 30, 2017, 10:22pm

Apa102 LEDs have a global brightness control setting you can use to reduce brightness by another 5 bits. I talk about it a bit in this long thread and have some code. Also look for the cpldcpu link for more in depth details.

I’m a backer of your matrix panels by the way, cool design! http://community.particle.io - SmartMatrix APA102 Library / Open Hardware Photon APA102 Shield - Libraries - Particle

marmil · April 30, 2017, 10:54pm

I’ll throw one other thought out here. I’ve found that some patterns/animations tend to start pulsing/stuttering/having very apparent brightness stepping at very low brightness values. For this reason I prefer to use higher brightness values and darken if needed with diffusion, so when I do darken things down I still get smooth animations.

Justin_Shaw · April 30, 2017, 11:53pm

@Louis_Beaudoin , Hey!! Thanks for your support! I’ll definitely check out your brightness control. Do you think it could be used in conjunction with FastLED?

Louis_Beaudoin · May 1, 2017, 12:22am

You can’t use GBC without modifying the FastLED library code. I’m not exactly sure where in the FastLED code to change it, but you need to change the first 0xFF byte shifted out per LED to be (0xE0 | your_gbc_value). It’s a bit of a hack for now.

It’s likely this line of code or somewhere slighly below:

github.com

FastLED/FastLED/blob/03d12093a92ee2b64fabb03412aa0c3e4f6384dd/chipsets.h#L166


/// @tparam SPI_SPEED the clock divider used for these leds.  Set using the DATA_RATE_MHZ/DATA_RATE_KHZ macros.  Defaults to DATA_RATE_MHZ(12)
template <uint8_t DATA_PIN, uint8_t CLOCK_PIN, EOrder RGB_ORDER = RGB, uint8_t SPI_SPEED = DATA_RATE_MHZ(12)>
class APA102Controller : public CPixelLEDController<RGB_ORDER> {
	typedef SPIOutput<DATA_PIN, CLOCK_PIN, SPI_SPEED> SPI;
	SPI mSPI;

	void startBoundary() { mSPI.writeWord(0); mSPI.writeWord(0); }
	void endBoundary(int nLeds) { int nDWords = (nLeds/32); do { mSPI.writeByte(0xFF); mSPI.writeByte(0x00); mSPI.writeByte(0x00); mSPI.writeByte(0x00); } while(nDWords--); }

	inline void writeLed(uint8_t b0, uint8_t b1, uint8_t b2) __attribute__((always_inline)) {
		mSPI.writeByte(0xFF); mSPI.writeByte(b0); mSPI.writeByte(b1); mSPI.writeByte(b2);
	}

public:
	APA102Controller() {}

	virtual void init() {
		mSPI.init();
	}

protected:

More details here: control global brightness on APA102 (and other chip supporting it) · Issue #91 · FastLED/FastLED · GitHub

Leon_Yuhanov · May 1, 2017, 12:41am

@Justin_Shaw If you want to overload FastLEDs colour system have a look at my color rendering system https://github.com/leonyuhanov/rpi_apa102driver/blob/master/spi.cpp Look specifically at the getColour() Function. It allows you to set a maximum byte value and returns a color based on a scale form 0 to 6XmaxVlaue as represented by a rainbow

Justin_Shaw · May 1, 2017, 9:58am

Thanks @Leon_Yuhanov and @Louis_Beaudoin . I’ll let you know any progress I make on this.

Adam_Haile · May 3, 2017, 9:18pm

@Justin_Shaw - I’m super familiar with the APA102 FastLED code. @Louis_Beaudoin 's hack should be easy enough and I’ll help you.
Also… what voltage are you running the LEDs at? You can always just run at 3.5v or something.

Justin_Shaw · May 3, 2017, 9:44pm

Sweet. This is for a sunrise clock, so need full brightness too.