add Analog In/Out examples

APIs_Drivers/AnalogIn_ex_1/README.md

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+# AnalogIn example
+
+This example shows how to control an R/C servo with analog input.

APIs_Drivers/AnalogIn_ex_1/main.cpp

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+/*
+ * Copyright (c) 2017-2020 Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#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);
+    }
+}

APIs_Drivers/AnalogIn_ex_2/README.md

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+# AnalogIn example
+
+This example shows how to sample analog signal, reading 16-bit normalized samples with AnalogIn.

APIs_Drivers/AnalogIn_ex_2/main.cpp

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+/*
+ * Copyright (c) 2017-2020 Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "mbed.h"
+
+AnalogIn input(A0);
+
+#define NUM_SAMPLES 1024
+
+int main()
+{
+    uint16_t samples[NUM_SAMPLES];
+
+    for (int i = 0; i < NUM_SAMPLES; i++) {
+        samples[i] = input.read_u16();
+        ThisThread::sleep_for(1);
+    }
+
+    printf("Results:\n");
+    for (int i = 0; i < NUM_SAMPLES; i++) {
+        printf("%d, 0x%04X\n", i, samples[i]);
+    }
+}

APIs_Drivers/AnalogIn_ex_3/README.md

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+# AnalogIn example
+
+This example showcases AnalogIn. Applying a voltage across the analog input pin causes the LED to light up. You can test this with a small wire connected to VCC. 

APIs_Drivers/AnalogIn_ex_3/main.cpp

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+/*
+ * Copyright (c) 2017-2020 Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "mbed.h"
+
+// Initialize a pins to perform analog input and digital output functions
+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());
+        ThisThread::sleep_for(200);
+    }
+}

APIs_Drivers/AnalogOut_ex_1/README.md

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+# AnalogOut example
+
+This example shows how to generat a sine wave on analog output.
+
+**Note:** Adjust the analog output pin name to your board specification.

APIs_Drivers/AnalogOut_ex_1/main.cpp

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+/*
+ * Copyright (c) 2017-2020 Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "mbed.h"
+
+const double pi = 3.141592653589793238462;
+const double amplitude = 0.5f;
+const double offset = 65535 / 2;
+
+// The sinewave is created on this pin
+// Adjust analog output pin name to your board spec.
+AnalogOut aout(A5);
+
+int main()
+{
+    double rads = 0.0;
+    uint16_t sample = 0;
+
+    while (1) {
+        // sinewave output
+        for (int i = 0; i < 360; i++) {
+            rads = (pi * i) / 180.0f;
+            sample = (uint16_t)(amplitude * (offset * (cos(rads + pi))) + offset);
+            aout.write_u16(sample);
+        }
+    }
+}

APIs_Drivers/AnalogOut_ex_2/README.md

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+# AnalogOut example
+
+This example shows how to set a specified voltage level on analog output. In the example, voltage is repeatedly raised from 0V to VCC on the output pin in 0.1*VCC V increments. The voltage values are printed to console.
+
+**Note:** Adjust the analog output pin name to your board specification.

APIs_Drivers/AnalogOut_ex_2/main.cpp

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+/*
+ * Copyright (c) 2017-2020 Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "mbed.h"
+
+// Initialize a pins to perform analog and digital output functions
+// Adjust analog output pin name to your board spec.
+AnalogOut  aout(A5);
+DigitalOut dout(LED1);
+
+int main(void)
+{
+    while (1) {
+        // change the voltage on the digital output pin by 0.1 * VCC
+        //  and print what the measured voltage should be (assuming VCC = 3.3v)
+        for (float i = 0.0f; i < 1.0f; i += 0.1f) {
+            aout = i;
+            printf("aout = %1.2f volts\n", aout.read() * 3.3f);
+            // turn on the led if the voltage is greater than 0.5f * VCC
+            dout = (aout > 0.5f) ? 1 : 0;
+            ThisThread::sleep_for(1000);
+        }
+    }
+}