Can the nRF52840 MCU power LED direct?

[ctchong]

I'm planning to connect The nRF52840 MCU GPIO in series to a 1.8V 20mA LED and a Resistor then to ground. 

Would the current from the MCU be sufficient to power the LED ? 

Thank you 

[ctchong]

Hi, 

How do you configure a GPIO to current sink? 

I tried the following but it doesn't seem to work. 

nrf_gpio_cfg(LED_1,NRF_GPIO_PIN_DIR_OUTPUT,
NRF_GPIO_PIN_INPUT_DISCONNECT,
NRF_GPIO_PIN_NOPULL,
NRF_GPIO_PIN_H0H1,
NRF_GPIO_PIN_NOSENSE);

nrf_gpio_pin_write(LED_1,0);

Thank you 

Best regards,

Chong 

[awneil]

ctchong said:

How do you configure a GPIO to current sink? 

It's not about the GPIO configuration - it's how you connect the LED.

How to properly post source code:

[ctchong]

nrf_gpio_cfg_output(led_pin);
nrf_gpio_cfg(LED_1,NRF_GPIO_PIN_DIR_OUTPUT,
                NRF_GPIO_PIN_INPUT_DISCONNECT,
                NRF_GPIO_PIN_NOPULL,
                NRF_GPIO_PIN_H0D1,      
                NRF_GPIO_PIN_NOSENSE);
                
nrf_gpio_pin_write(led_pin, 0);
nrf_gpio_pin_write(LED_1,0);

I am connecting the LED like Figure 1: +V is 3.3V and PORT Pin is configured as LED_1 and led_pin. I have 2 LEDs configured as the same connection.

Both GPIO codes don't work.

Thank you 

Best regards,

Chong 

[hmolesworth]

Which pins are you using for led_pin and LED_1? P1.x pins do not have high drive capability (NRF_GPIO_PIN_H0D1), nor do some P0.x pins; this is sometimes overlooked .. Also be aware that if 3.3V is very much higher than your nRF52840 i/o voltage there may be issues with back-drive (phantom power) into the port pin.

[ctchong]

Hi 

I'm using P0.11 P0.12 P1.06 P1.07 

All P1.x have no high drive capability? 

Thank you 

[awneil]

hmolesworth said:

P1.x pins do not have high drive capability (NRF_GPIO_PIN_H0D1), nor do some P0.x pins

It was just a quick look, but I couldn't see that mentioned in the Product Specification ?

[awneil]

ctchong said:

Both GPIO codes don't work

As with debugging any problem, you need to take this one step at a time.

For a start, have you tried using an unmodified SDK example on a DevKit? That is always the best place to start - giving you a known-good basis to work from.

In your circuit:

1. If you disconnect the LED cathode from the port pin, and ground it - does the LED light.
2. With the LED disconnected, can you see the pin level changing; eg, on a scope or meter?
3. Run you code in the debugger - is it actually reaching the point(s) that configure the pins, & change the output?

How To Debug