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Why doesn't my LED get any light by using MM5451 LED driver?

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I'm using an mbed micro controller to switch on all channels on the MM5451 LED driver. I have wired accordingly with 5v PSU, 1k resistor on pin 19 for brightness control (have varied this with no results), data/clock, LEDs with negative to the MM5451 (and positive to +5v inc resistors).

I've got a very basic loop that sends out a string of pulses (35 + start bit) which should switch on all channels, but I'm not getting any light.


#include "mbed.h"

DigitalOut dat(p22);
DigitalOut clk(p21);

int main() {
    while(1) {
        for(int i = 1;i < 37; i++){
            dat = 1;
            clk = 1;
            clk = 0;
            dat = 0;


mbed: NXP LPC1768

Here's an image of the output pulses:


Hopefully the chip isn't broken and I'm just making a really stupid error. Looking forward to your answers!

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