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AnalogIn

Use the AnalogIn API to read an external voltage applied to an analog input pin. AnalogIn() reads the voltage as a fraction of the system voltage. The value is a floating point from 0.0(VSS) to 1.0(VCC). For example, if you have a 3.3V system and the applied voltage is 1.65V, then AnalogIn() reads 0.5 as the value.

Note: Only certain pins are capable of making these measurements, so check the pinmap of your board for compatible pins.

AnalogIn class reference

Public Member Functions
 AnalogIn (PinName pin)
float read ()
unsigned short read_u16 ()
 operator float ()
Protected Member Functions
virtual void lock ()
virtual void unlock ()
Protected Attributes
analogin_t _adc
Static Protected Attributes
static SingletonPtr< PlatformMutex_mutex

AnalogIn hello, world

/* mbed Example Program
 * Copyright (c) 2006-2014 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#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", ain.read()*100.0f);
        printf("normalized: 0x%04X \n", ain.read_u16());
        wait(0.2f);
    }
}

AnalogIn examples

Example one

Control an R/C servo with analog input.

#include "mbed.h"

AnalogIn position(A0);
PwmOut servo(D3);

int main() {
    // servo requires a 20ms period    
    servo.period(0.020f);
    while (1) {
        // servo position determined by a pulse width between 1-2ms
        servo.pulsewidth(0.001f + 0.001f * position);
    }
}

Example two

This example shows AnalogIn reading 16-bit normalized samples.

#include "mbed.h"

AnalogIn input(A0);

int main() {
    uint16_t samples[1024];

    for(int i=0; i<1024; i++) {
        samples[i] = input.read_u16();
        wait(0.001f);
    }

    printf("Results:\n");
    for(int i=0; i<1024; i++) {
        printf("%d, 0x%04X\n", i, samples[i]);
    }
}   

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