Adds a calibration sample

code/calibration/.gitignore

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+build
+build_*

code/calibration/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(calibration)
+
+target_sources(app PRIVATE src/main.c)

code/calibration/README.md

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+# Calibration
+A sample for calibrating b-parasites soil moisture analog-to-digital conversion.

code/calibration/boards

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+../nrf-connect/boards

code/calibration/dts

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+../nrf-connect/dts

code/calibration/prj.conf

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+CONFIG_PINCTRL=y
+CONFIG_LOG=y
+CONFIG_PWM=y
+CONFIG_PWM_LOG_LEVEL_DBG=y
+CONFIG_CBPRINTF_FP_SUPPORT=y
+CONFIG_ADC=y
+CONFIG_GPIO=y
+CONFIG_PM=y
+CONFIG_PM_DEVICE=y
+CONFIG_USE_SEGGER_RTT=y

code/calibration/src/main.c

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+#include <drivers/adc.h>
+#include <drivers/gpio.h>
+#include <drivers/pwm.h>
+#include <logging/log.h>
+#include <zephyr/zephyr.h>
+
+LOG_MODULE_REGISTER(main, LOG_LEVEL_DBG);
+
+#define PRST_STRINGIFY(x) #x
+#define PRST_TO_STRING(x) PRST_STRINGIFY(x)
+#define PRST_LOCATION __FILE__ ":" PRST_TO_STRING(__LINE__)
+
+#define RET_IF_ERR_MSG(expr, msg)                  \
+  {                                                \
+    int err = (expr);                              \
+    if (err) {                                     \
+      LOG_ERR("Error: " msg " in " PRST_LOCATION); \
+      return err;                                  \
+    }                                              \
+  }
+
+#define RET_IF_ERR(expr) RET_IF_ERR_MSG(expr, "")
+
+static const struct pwm_dt_spec soil_pwm_dt =
+    PWM_DT_SPEC_GET(DT_NODELABEL(soil_pwm));
+static const uint32_t pulse = DT_PROP(DT_NODELABEL(soil_pwm), pulse);
+
+struct gpio_dt_spec fast_disch_dt =
+    GPIO_DT_SPEC_GET(DT_NODELABEL(fast_disch), gpios);
+
+static const struct adc_dt_spec adc_soil_spec =
+    ADC_DT_SPEC_GET_BY_IDX(DT_PATH(zephyr_user), 0);
+
+static const struct adc_dt_spec adc_batt_spec =
+    ADC_DT_SPEC_GET_BY_IDX(DT_PATH(zephyr_user), 2);
+
+static int16_t soil_buf;
+static struct adc_sequence soil_sequence = {
+    .buffer = &soil_buf,
+    .buffer_size = sizeof(soil_buf),
+};
+
+static int16_t batt_buf;
+static struct adc_sequence batt_sequence = {
+    .buffer = &batt_buf,
+    .buffer_size = sizeof(batt_buf),
+};
+
+int main(void) {
+  RET_IF_ERR(!device_is_ready(fast_disch_dt.port));
+  RET_IF_ERR(!device_is_ready(soil_pwm_dt.dev));
+
+  // Configure analog-to-digital channels.
+  RET_IF_ERR(adc_channel_setup_dt(&adc_soil_spec));
+  RET_IF_ERR(adc_channel_setup_dt(&adc_batt_spec));
+
+  // Configure fast discharge enable pin.
+  RET_IF_ERR(gpio_pin_configure_dt(&fast_disch_dt, GPIO_OUTPUT));
+
+  // Enable fast discharge circuit.
+  RET_IF_ERR(gpio_pin_set_dt(&fast_disch_dt, 1));
+
+  // Start PWM.
+  RET_IF_ERR(pwm_set_dt(&soil_pwm_dt, soil_pwm_dt.period, pulse));
+
+  RET_IF_ERR(adc_sequence_init_dt(&adc_soil_spec, &soil_sequence));
+  RET_IF_ERR(adc_sequence_init_dt(&adc_batt_spec, &batt_sequence));
+
+  LOG_INF("input_voltage;soil_adc_output");
+  while (true) {
+    k_msleep(500);
+
+    RET_IF_ERR(adc_read(adc_batt_spec.dev, &batt_sequence));
+    int32_t batt_val_mv = batt_buf;
+    RET_IF_ERR(adc_raw_to_millivolts_dt(&adc_batt_spec, &batt_val_mv));
+
+    RET_IF_ERR(adc_read(adc_soil_spec.dev, &soil_sequence));
+    int32_t soil_val_mv = soil_buf;
+    RET_IF_ERR(adc_raw_to_millivolts_dt(&adc_soil_spec, &soil_val_mv));
+
+    LOG_INF("%.2f;%u", batt_val_mv / 1000.0f, soil_buf);
+  }
+}