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STM_8: Controlling Smart LED stripe
A Smart LED stripe is a chain of connected digital LEDs (also referenced as NEOPIXEL) which can be individually controlled. The stripe in our lab equipment consists of eight RGB LEDs. There exist also other configurations such as RGBWW (Red+Green+Blue+Warm White+Cold White) or WWA (Warm White+Cold White+Amber). They are controlled with just one pin/GPIO. GPIO sends the digital signal to the first LED in a chain and the LED passes data to the next one, and so on.
The most common type of LED stripes is WS2812B (RGB). Initially LED Stripes were powered with 5V, but that limits the length of the chain up to some 1-2m (because of the voltage drop), so nowadays LED stripes powered with 12V and even 24V are getting more and more popular.
In this scenario, you will learn how to control a small LED RGB Stripe, composed of 8 Smart (Digital) LEDs with STM32 SoC.
Prerequisites
Familiarise yourself with a hardware reference on the LED Stripe. It is controlled with a single GPIO (D8 in Arduino style naming, or PC_12 in Nucleo style naming), as presented in the “Table 1: STM32WB55 Node Hardware Details” on the hardware reference page. To control a WS2812B LED stipe, we will use a library:
adafruit/Adafruit NeoPixel@^1.12.0
Note, this library can also control other RGB LED stripes than WS2812B.
There are at least two ways (algorithms) to implement this task:
- using the blocking (
delay(…);) function calls in thevoid loop();or, - using a timer (see advanced scenario).
Suggested Readings and Knowledge Resources
Hands-on Lab Scenario
Task to be implemented
Implement a rainbow of colours flowing through the LED Stripe.
Note, do not change colours too fast, as you won't be able to observe changes via the video stream. An update once per second is usually suitable.
Start
When booking a device, ensure the LED stripe is visible in the camera.
Due to the low camera dynamics, do not use the full brightness of the LEDs: off is equivalent to 0, and the full brightness of the colour is 255 (8-bit resolution, per colour). We suggest to use up to 60 or max 100.
Because of the camera and human eye characteristics, the same numerical brightness set for one colour can bring a much different brightness experience on another, so setting up 60 to channel Red will have a different overall experienced brightness than setting 60 to channel Blue or Green.
Steps
Below, we provide a sample colour configuration that does not reflect the desired effect that should result from the exercise. It is just for instructional purposes. You need to invent how to implement a rainbow effect yourself.
Step 1
Include necessary library:
#include "Freenove_WS2812_Lib_for_ESP32.h"
Step 2
Declare configuration and a controller class:
#define WLEDS_COUNT 8 #define WLEDS_PIN 34 #define WLEDS_CHANNEL 0 static Freenove_ESP32_WS2812 stripe = Freenove_ESP32_WS2812(WLEDS_COUNT, WLEDS_PIN, WLEDS_CHANNEL, TYPE_GRB);
Step 3
To switch a particular LED, use the following function:
stripe.setLedColorData(1,60,0,0); //light Red of the 2nd LED stripe.show(); //Writes colours to the LED stripe
Parameters are: setLedColorData(int index, u8 r, u8 g, u8 b);.
Note that the index is 0-based, so in the case of our device, valid indexes are 0…7.
If you want to set all LEDs in the stripe to the same colour, there is a handy function: setAllLedsColorData(u8 r, u8 g, u8 b);.
Remember to use the show(); function afterwards.
Result validation
Observe the flow of the colours via the stripe.
FAQ
I cannot see the colour via the video camera - everything looks white…: Try to lower the LED's brightness.
