Working with LEDs and RGB LED strips

An LED is a special type of diode. While most diodes have a low forward voltage of around 0.6 volts, LEDs have a high forward voltage depending on the color of the light:

• Red: 1.6 to 2.0 volts.
• Green: 1.9 to 4.0 volts.
• Blue: 2.5 to 3.7 volts.

An RGB LED is the physical combination of three LEDs: red, green and blue. As a result, a forward voltage of around 3.5 volts is required to light them.

The ESP32 hardware operates at 3.3 volts, which is not enough to light some of these LEDs. For this reason, you may need a different power source, which is labelled VLed in this project. There are a number of options available:

• 3.3V power sources

  Some LEDs will work with a 3.3 volt power supply. Attach VLed to 3V3.

• 5 volts power sources (and higher)

  Wheel bases and USB cables already operate at 5 volts, which is enough to power any LED. Attach VLed to 5V if available.

  Higher voltages will work as long as you use a proper current limiting resistor for each LED. When working with LED strips, make sure your power source is within its specifications.

• External powerboost module/shield

  As described in the power subsystem, some external power boost modules provide both 5.0 and 3.3 volt outputs. Attach VLed to the 5V output.

• Builtin powerboost module/shield

  If your DevKit board has built-in battery support, there is no 5V output. Connect VLed directly to the positive pole of the battery. This is not optimal as some LEDs will go off before the battery is discharged.

RGB LED strips

LED strips are controlled by a single output-capable pin labelled Dout in this project. Some LED strips can work with 3.3V logic, others cannot. If your LED strip does not work with 3.3V logic, you will need a small "level shifter" circuit, which is described below.

• No level shifter (3.3V logic)

  Wire Dout to Din in the first pixel via a 300 to 1000 ohm resistor. The resistor should be at the end of the wire closest to the LED strip, not the DevKit board. This resistor can be omitted only if your LED strip already has a resistor in Din. Otherwise your LED strip could burn out.

  

  Show at falstad.com

  Needed parts:

  • 300 to 500 ohm resistor (x1)

• Level shifter (5V logic)

  Din requires a minimum voltage of 3.5 volts. The ESP32 operates at 3.3 volts, which is insufficient. To overcome this limitation, a "level shifter" circuit is required. We are using the most simple level shifter available: a pull resistor attached to a GPIO pin in open drain mode (Dout).

  

  Test this circuit at falstad.com

  Needed parts:

  • 1K-ohms resistor (x1)

Each individual RGB pixel is controlled by a (very small) chip, called pixel driver. This project supports the following:

• WS2811 drivers. Note: not tested.
• The WS2812 family, including: WS2812 and WS2812B
• The WS2815 family. Note: not tested.
• SK6812 drivers. Note: not tested.
• UCS1903 drivers. Note: not tested.
• APA106 drivers.