Nucleo F303K8 AnalogIn does not work

Mbed OS
1

I just picked up the Nucleo F303K8 dev board to test out the on board ADC found in the STM32 line and could use some help troubleshooting why I cannot get any valid reading from the pin.

The signal I am attempting to read is the output from a potentiometer connected to GND and VDD.

#include <mbed.h>

Serial pc(USBTX, USBRX);
DigitalOut led(LED1);
AnalogIn a1(A2);

int main() {

  while(1) {
    float val = a1.read();
    pc.printf("val: %d \r\n", a1.read());    // this spits out random Unsigned decimal integer
    if (val > 1) {
      led.write(1);
    } else {
      led.write(0);
    }
  }
}

Now what I expect this program to do when run is output the a1.read() value to the console, as well as turn on/off the onboard led, but what actually happens is the led does NOT get lit up, and the serial output is just a bunch of random “Unsigned decimal integers” like so:

val: 0 
val: 0 
val: 0 
val: 0 
val: -1073741824 
val: 536870912 
val: 536870912 
val: 0 
val: 0 
val: 0 
val: -536870912 
val: 0 
val: -2147483648 
val: 0 
val: 0 
val: 536870912 
val: 0 
val: 536870912 
val: -1610612736
2

Hi Scott,
I checked your program with my F303K Mbed board and confirmed the output data.
I could reproduce problem.
Please modify your source code as follows.

pc.printf("val: %f\r\n", a1.read());

%d ->%f

Maybe you can read correct value from 0.0 to 1.0.

Kenji Arai

3

Hey Kenji, thanks for checking for me. It still doesn’t seem to work. Strange how yours is working and mine isn’t though…

4

ya so I think I misinterpretted what read() returns. Its actually a float between 0.0 and 1.0, so after updating my LED if statements I was able to toggle the LED on/off based on voltage being read, however I am still unable to see the float value in the console. I want to say it has something to do with this

5

Hi Scott,
please make a copy&paste followings.

#include <mbed.h>

DigitalOut led(LED1);
AnalogIn a2(A2);

int main() {
  while(1) {
    float val = a2.read();
    printf("val: %4.3f\r\n", val);
    if (val > 0.5f) {
      led = 1;
    } else {
      led = 0;
    }
    wait(0.2f);
  }
}

I slightly modified your code for better understanding.
Please make sure your mbed revision.
I’m using 20 Feb 2019, release version 165.

revision
revision870×32 11.9 KB

Just in case, I created bin file and save it into below.
It works on my F303K8 Mbed.
https://onedrive.live.com/?id=E726C1E354E854B2%211099537&cid=E726C1E354E854B2

Kenji Arai

6

Ahoj,

just for info, code like this already exist in examples and it is working (tested) -Nucleo_read_analog_value
In comments of that code you can found also a description.

BR, Jan