Peter Xian

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10 years, 8 months ago.

AnalogIn() for STM32F401RE is performing unexpectedly

I have the following program running to test the ADC on STM32F401RE. However, when I connect the A0 to 5V, it's showing 74% and if I leaving it off, it's showing 35%. When I connect it to GND, it's showing close to 0%. I'm not sure why 5V is mapped to only 74% of the analogy input. Does anyone know why?

#include "mbed.h"
 
// Initialize a pins to perform analog input and digital output fucntions
AnalogIn   ain(A0);
DigitalOut dout(LED1);
 
int main(void)
{
    while (1) {
        // test the voltage on the initialized analog pin
        //  and if greater than 0.3 * VCC set the digital pin
        //  to a logic 1 otherwise a logic 0
        if(ain > 0.3f) {
            dout = 1;
        } else {
            dout = 0;
        }
        
        // print the percentage and 16 bit normalized values
        printf("percentage: %3.3f%%\n\r", ain.read()*100.0f);
        printf("normalized: 0x%04X \n\r", ain.read_u16());
        wait(3);
    }
}

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Last updated: 10 Dec 2014
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