tests: Add test for AD7746 driver

tests/driver_ad7746/Makefile

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+include ../Makefile.tests_common
+
+USEMODULE += ad7746
+USEMODULE += xtimer
+
+include $(RIOTBASE)/Makefile.include

tests/driver_ad7746/README.md

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+# About
+This is a test application for the AD7746 capacitance-to-digital converter with
+temperature and voltage sensors.
+
+# Usage
+This test application will initialize the sensor for measuring capacitance from
+the CIN1 input (it can be changed in runtime). It will also initialize the
+voltage / temperature channel and show that the mode can be changed in runtime.
+
+After that it will print measurements of capacitance and internal temperature
+on STDOUT.

tests/driver_ad7746/main.c

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+/*
+ * Copyright (C) 2019 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup tests
+ * @{
+ *
+ * @file
+ * @brief       Test application for the AD7746 capacitance-to-digital
+ *              converter with temperature sensor.
+ *
+ * @author      Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
+ * @}
+ */
+
+#include <stdio.h>
+
+#include "xtimer.h"
+#include "timex.h"
+#include "ad7746.h"
+#include "ad7746_params.h"
+
+#define SLEEP       (1000 * US_PER_MS)
+
+static ad7746_t dev;
+
+int main(void)
+{
+    int data;
+
+    puts("AD746 capacitance to digital driver test application\n");
+    printf("Initializing AD7746 at I2C_DEV(%i)... ",
+           ad7746_params->i2c);
+
+    if (ad7746_init(&dev, ad7746_params) == AD7746_OK) {
+        puts("[OK]\n");
+    }
+    else {
+        puts("[Failed]");
+        return -1;
+    }
+
+    /* show that if changed mode data may not be available right away */
+    if (ad7746_read_voltage_vdd(&dev, &data) == AD7746_OK) {
+        printf("VDD : %d mV\n", data);
+    }
+    else {
+        printf("No data available for VDD yet\n");
+    }
+
+    if (ad7746_read_temperature_int(&dev, &data) == AD7746_OK) {
+        printf("Internal temperature: %d C\n", data);
+    }
+    else {
+        printf("No data available for internal temperature yet\n");
+    }
+
+    while (1) {
+        int res;
+        puts("=========================");
+        puts("        Measuring");
+        puts("=========================");
+        res = ad7746_read_capacitance_1(&dev, &data);
+        if ( res == AD7746_OK) {
+            printf("Capacitance %d fF\n", data);
+        }
+        else {
+            printf("Error reading data. err: %d\n", res);
+        }
+
+        do {
+            res = ad7746_read_temperature_int(&dev, &data);
+        } while (res == AD7746_NODATA);
+
+        if (res == AD7746_OK) {
+            printf("Internal temperature: %d C\n", data);
+        }
+        else {
+            printf("Error reading internal temperature\n");
+        }
+        puts("");
+        xtimer_usleep(SLEEP);
+    }
+
+    return 0;
+}