Microbit

Microbit V1 display driver

FrankLeave a comment

The image above shows a Microbit V1 connected to an ST7789 1.14′ display via a Kitronik breakout board. The SPI interface on the Microbit (NRF51822) is a little slow at 4MHz but it is ok for simple outputs as shown above. Code was developed using VSCode, PlatformIO the mbed framework. The full list of connections can be found in the file display.cpp which is available on the github repo over here

Using the HD107S RGB Led with a BBC Microbit

Frank2 Comments

The HD107S is a low cost RGB LED unit which features an SPI interface. I paid just over €9 for 50 of them. They are quite easy to program using a microcontroller platform such as the BBC Microbit. The short program below was written on MBed and downloaded to the Microbit. It causes the LED to cycle through a range of colours.

#include "mbed.h"

SPI spi(P0_21, P0_22, P0_23); // mosi, miso, sclk
void getRainbow(unsigned &Red, unsigned &Green, unsigned &Blue);

int main() {

    unsigned Red,Green,Blue;
    Red = Green = Blue = 0;    
    char tx_buffer[16];
    char rx_buffer[16];
    spi.format(8, 3);
    spi.frequency(1000000);
    tx_buffer[0]=0; // header
    tx_buffer[1]=0; // header
    tx_buffer[2]=0; // header
    tx_buffer[3]=0; // header
    tx_buffer[4]=0xe0 + 0x1f; // max brightness (1f = brightness figure - lower to suit)
    while(1) {
        getRainbow(Red,Green,Blue);
        tx_buffer[5]=Blue; // blue
        tx_buffer[6]=Green; // green
        tx_buffer[7]=Red; // red        
        spi.write(tx_buffer, 8, rx_buffer, 0);              
        wait(0.01);
        
        
    }
}
void getRainbow(unsigned &Red, unsigned &Green, unsigned &Blue)
{   // Cycle through the colours of the rainbow (non-uniform brightness however)
    // Inspired by : http://academe.co.uk/2012/04/arduino-cycling-through-colours-of-the-rainbow/    
    static int State = 0;
    switch (State)
    {
        case 0:{
            Green++;
            if (Green == 255)
                State = 1;
            break;
        }
        case 1:{
            Red++;
            if (Red == 255)
                State = 2;
            break;
        }
        case 2:{
            Blue++;
            if (Blue == 255)
                State = 3;          
            break;
        }
        case 3:{
            Green--;
            if (Green == 0)
                State = 4;
            break;
        }
        case 4:{
            Red--;
            if (Red == 0)
                State = 5;
            break;
        }
        case 5:{
            Blue --;
            if (Blue == 0)
                State = 0;
            break;
        }       
    }    
}