Overview

The APA102 (sold by Adafruit under the brand name DotStar) is an individually addressable RGB LED light source with an integrated CMOS control IC in a 5050 SMD package.

Unlike the ubiquitous WS2812B (NeoPixel), which relies on a strict single-wire 800 kHz800\text{ kHz} timing protocol that requires microsecond-accurate bit-banging and disables interrupts on 8-bit MCUs, the APA102 uses a standard 2-wire SPI protocol (Clock and Data). This allows transmission rates up to 20 MHz, enables high-speed PWM dimming (19.2 kHz PWM rate vs WS2812B's 400 Hz), and eliminates timing sensitivity when driven from non-realtime operating systems like Raspberry Pi Linux.

Quick reference

Supply voltage (VCC)4.5 V to 5.5 V DC (5.0 V nominal)
Protocol2-Wire SPI (Serial Clock CKI, Serial Data SDI)
Max SPI clock rateUp to 20 MHz
Internal PWM frequency19.2 kHz (flicker-free high-speed persistence of vision)
Color depth24-bit RGB (8 bits per channel) + 5-bit global brightness (32 levels)
Max current draw~60 mA per LED at 100% full white (VCC=5.0VV_{CC} = 5.0\text{V})

Pinout & Connector

APA102 LEDs are integrated on strips or matrices exposing a 4-wire interface:

LeadCable ColorNameTypeDescription
1RedVCCPowerSupply voltage (+5.0 V DC)
2Green / YellowCKI / CIDigital InputSerial Clock Input
3Blue / WhiteSDI / DIDigital InputSerial Data Input
4BlackGNDPowerGround (0 V)

(Signal outputs on the far end of an LED strip are labeled CKO and SDO for cascading to the next strip segment).

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVCCV_{CC}4.55.05.5VDC
Logic Input VoltageVINV_{IN}-0.55.0VCC+0.5V_{CC}+0.5VCKI, SDI pins
Max Clock FrequencyfCLKf_{CLK}—15.020.0MHzSPI bus clock
Internal PWM RatefPWMf_{PWM}—19.2—kHzLED current modulation rate
Red LED Peak WavelengthλR\lambda_R620625630nmBrightness ~400 mcd
Green LED Peak WavelengthλG\lambda_G520522.5525nmBrightness ~1200 mcd
Blue LED Peak WavelengthλB\lambda_B465467.5470nmBrightness ~300 mcd

Data Framing & SPI Protocol

A complete data frame for an APA102 LED strip consists of 3 distinct sections:

  1. Start Frame: 32 zero bits (0x00 0x00 0x00 0x00).
  2. LED Data Frames (4 bytes per LED):
    • Byte 0: 111 + 5-bit Global Brightness (0xE0 | 0x00–0x1F).
    • Byte 1: Blue brightness (0x00–0xFF).
    • Byte 2: Green brightness (0x00–0xFF).
    • Byte 3: Red brightness (0x00–0xFF).
  3. End Frame: ⌈N2⌉\lceil \frac{N}{2} \rceil bits of High (0xFF) pulses (or NN clock pulses) to push remaining bits through internal shift registers to the last LED on long strips (N=number of LEDsN = \text{number of LEDs}).
text
[Start Frame 4B] -> [LED 1: 4B] -> [LED 2: 4B] ... -> [LED N: 4B] -> [End Frame]

Wiring

APA102 Lead→Arduino / MCURaspberry PiNotes
VCC5V Power Supply5V Power SupplyDo not power long strips from MCU 5V pin
GNDGNDGNDCommon ground mandatory
CKI (Clock)Digital D13 (SCK)GPIO 11 (SPI0_SCLK)Hardware or Software SPI Clock
SDI (Data)Digital D11 (MOSI)GPIO 10 (SPI0_MOSI)Hardware or Software SPI Data
Warning

High current supply hazard:

  • A strip of 60 APA102 LEDs draws up to 3.6 A at full white brightness (60 mA×60=3600 mA60\text{ mA} \times 60 = 3600\text{ mA}).
  • Always use an external 5V DC high-current power supply and inject power at both ends of strips longer than 2 meters to prevent copper voltage drop (which causes color shifting towards red at the tail end).

Example

cpp
#include <Adafruit_DotStar.h>
#include <SPI.h>

#define NUMPIXELS 30 // Number of LEDs in strip

// Hardware SPI setup (using SPI MOSI and SCK pins)
Adafruit_DotStar strip(NUMPIXELS, DOTSTAR_BRG);

void setup() {
  strip.begin(); // Initialize pins for output
  strip.setBrightness(80); // Set global brightness (0 to 255)
  strip.show(); // Turn all LEDs off
}

void loop() {
  // Chase a blue light down the strip
  for(int i=0; i<NUMPIXELS; i++) {
    strip.setPixelColor(i, 0x0000FF); // Blue color (0xRRGGBB)
    strip.show();
    delay(30);
    strip.setPixelColor(i, 0); // Turn off
  }
}

Common mistakes

  • Leaving ground un-connected to MCU: Connecting external 5V power without connecting external GND to MCU GND causes severe data corruption and flickering.
  • Conflating RGB and BGR byte order: APA102 LEDs from different manufacturers use different internal byte sequences (DOTSTAR_BGR, DOTSTAR_RGB, or DOTSTAR_BRG). If colors are swapped, adjust the color-order parameter in software.

Notes

  • APA102 vs WS2812B: APA102 uses 19.2 kHz19.2\text{ kHz} internal PWM (flicker-free for high-speed photography/video recording and persistence-of-vision wands) compared to WS2812B's 400 Hz400\text{ Hz} PWM.

Assets & downloads