Puts soil moisture reading into the BLE advertisement packet

code/b-parasite/config/prst_config.h

@@ -7,11 +7,12 @@
 #define PRST_LED_PIN NRF_GPIO_PIN_MAP(0, 28)
 
 // Deep sleep.
-#define PRST_DEEP_SLEEP_IN_SECONDS 2
+#define PRST_DEEP_SLEEP_IN_SECONDS 3
 
 // Analog to digital converter (ADC).
-// Prints out ADC debug info, such as the values read for battery and soil moisture.
-#define PRST_ADC_DEBUG 1
+// Prints out ADC debug info, such as the values read for battery and soil
+// moisture.
+#define PRST_ADC_DEBUG 0
 
 // BLE.
 #define PRST_BLE_ADV_NAME "prst"
@@ -22,4 +23,7 @@
 #define PRST_PWM_PIN NRF_GPIO_PIN_MAP(0, 5)
 #define PRST_FAST_DISCH_PIN NRF_GPIO_PIN_MAP(1, 10)
 
+// SHT3C temp/humidity sensor.
+#define PRST_SHT3C_DEBUG 1
+
 #endif  // _PRST_CONFIG_H_

code/b-parasite/config/sdk_config.h

@@ -11343,7 +11343,7 @@
 // <2=> BLOCK_IF_FIFO_FULL
 
 #ifndef SEGGER_RTT_CONFIG_DEFAULT_MODE
-#define SEGGER_RTT_CONFIG_DEFAULT_MODE 2
+#define SEGGER_RTT_CONFIG_DEFAULT_MODE 0
 #endif
 
 // </h>

code/b-parasite/src/main.c

@@ -58,31 +58,22 @@ static void power_manage(void) {
 // Here we need to be extra careful with what operations we do. This callback
 // has to return fast-ish, otherwise we hit some hard exceptions.
 static void rtc_callback() {
-  NRF_LOG_INFO("Batt raw ");
-  NRF_LOG_FLUSH();
   nrf_gpio_pin_set(PRST_LED_PIN);
   prst_shtc3_read_t temp_humi = prst_shtc3_read();
   nrf_gpio_pin_set(PRST_FAST_DISCH_PIN);
   prst_pwm_init();
   prst_pwm_start();
   prst_adc_batt_read_t batt_read = prst_adc_batt_read();
-  int16_t soil_read = prst_adc_soil_read();
+  prst_adc_soil_moisture_t soil_read = prst_adc_soil_read();
   prst_pwm_stop();
   nrf_gpio_pin_clear(PRST_FAST_DISCH_PIN);
-  NRF_LOG_INFO("Read soil: %d", soil_read);
-  prst_ble_update_adv_data(batt_read.millivolts, temp_humi.temp_millicelcius, temp_humi.humidity, 0);
+  prst_ble_update_adv_data(batt_read.millivolts, temp_humi.temp_millicelcius,
+                           temp_humi.humidity, soil_read.relative);
   NRF_LOG_FLUSH();
   prst_adv_start();
   nrf_delay_ms(200);
   prst_adv_stop();
   nrf_gpio_pin_clear(PRST_LED_PIN);
-  UNUSED_VARIABLE(batt_read);
-  // NRF_LOG_INFO("Read batt: " NRF_LOG_FLOAT_MARKER " V (%d), %u mV",
-  //              NRF_LOG_FLOAT(batt_read.voltage), batt_read.raw, batt_read.millivolts);
-  // NRF_LOG_INFO("Read temp: " NRF_LOG_FLOAT_MARKER " oC",
-  //              NRF_LOG_FLOAT((float) temp_humi.temp_millicelcius / 1000.0));
-  // NRF_LOG_INFO("Read humi: " NRF_LOG_FLOAT_MARKER " %%",
-  //              NRF_LOG_FLOAT(100.0 * temp_humi.humidity / (1 << 16)));
   NRF_LOG_FLUSH();
 }
 
@@ -94,11 +85,18 @@ int main(void) {
   prst_ble_init();
   prst_adc_init();
   prst_shtc3_init();
+
+  // Set up RTC. It will call our custom callback at a regular interval, defined
+  // by PRST_DEEP_SLEEP_IN_SECONDS.
   prst_rtc_set_callback(rtc_callback);
   prst_rtc_init();
 
-  nrf_delay_ms(100);
+  // In addition to scheduling it, let's immediatelly call it - it makes
+  // debugging less tedious.
+  rtc_callback();
 
+  // Here we go into a low energy mode. The datasheet calls this mode "System
+  // ON", and in my tests it consumes around 2.7uA.
   for (;;) {
     power_manage();
   }

code/b-parasite/src/prst/adc.c

@@ -27,6 +27,11 @@ static nrf_saadc_value_t sample_adc_channel(uint8_t channel) {
   return result;
 }
 
+// Caps the argument to the [0, 1] range.
+static inline double cap_value(double value) {
+  return value > 1.0 ? 1.0 : (value < 0.0 ? 0.0 : value);
+}
+
 // Unused, since we'll call the SAADC synchronously for now.
 void saadc_callback(nrf_drv_saadc_evt_t const* p_event) {
   if (p_event->type == NRF_DRV_SAADC_EVT_DONE) {
@@ -69,16 +74,23 @@ prst_adc_batt_read_t prst_adc_batt_read() {
   ret.voltage = (3.6 * result) / (1 << PRST_ADC_RESOLUTION);
   ret.millivolts = ret.voltage * 1000;
 #if PRST_ADC_DEBUG
-  NRF_LOG_INFO("[adc] Read battery voltage: %d (raw); %d mV; ", ret.raw, ret.millivolts,
-               ret.voltage);
+  NRF_LOG_INFO("[adc] Read battery voltage: %d (raw); %d mV; ", ret.raw,
+               ret.millivolts, ret.voltage);
 #endif
   return ret;
 }
 
-int16_t prst_adc_soil_read() {
+prst_adc_soil_moisture_t prst_adc_soil_read() {
   nrf_saadc_value_t result = sample_adc_channel(PRST_ADC_SOIL_CHANNEL);
+  double percentage = cap_value(((double)result - PRST_SOIL_DRY) /
+                                (PRST_SOIL_WET - PRST_SOIL_DRY));
+  prst_adc_soil_moisture_t ret;
+  ret.raw = result;
+  ret.relative = percentage * (1 << 16);
 #if PRST_ADC_DEBUG
-  NRF_LOG_INFO("[adc] Read soil moisture: %d", result);
+  NRF_LOG_INFO("[adc] Read soil moisture: %d (raw); " NRF_LOG_FLOAT_MARKER
+               " %% (percentage); %u (relative)",
+               ret.raw, NRF_LOG_FLOAT(percentage * 100), ret.relative);
 #endif
-  return result;
+  return ret;
 }

code/b-parasite/src/prst/adc.h

@@ -3,16 +3,29 @@
 
 #include <stdint.h>
 
+// ADC values. Assumes 10 bits resolution.
+// TODO(rbaron) this values drift a little bit as the battery discharges.
+// I previously did a hacky linear regression to estimate them, but I'm
+// not super sure how useful that is.
+#define PRST_SOIL_WET 200
+#define PRST_SOIL_DRY 500
+
 typedef struct prst_adc_batt_val {
   int16_t raw;
   uint16_t millivolts;
   double voltage;
 } prst_adc_batt_read_t;
 
+typedef struct prst_adc_soil_moisture {
+  int16_t raw;
+  // A value from 0 (cmopletely dry) to 2^10 (completely wet).
+  uint16_t relative;
+} prst_adc_soil_moisture_t;
+
 void prst_adc_init();
 
 prst_adc_batt_read_t prst_adc_batt_read();
 
-int16_t prst_adc_soil_read();
+prst_adc_soil_moisture_t prst_adc_soil_read();
 
 #endif  // _PRST_ADC_H_

code/b-parasite/src/prst/shtc3.c

@@ -47,12 +47,16 @@ prst_shtc3_read_t prst_shtc3_read() {
   // TODO(rbaron): verify the CRC of the measurements. The function is described
   // in the datasheet.
 
-  NRF_LOG_INFO("Computing...");
   double temp_c = -45 + 175 * ((double)((buff[0] << 8) | buff[1])) / (1 << 16);
-  // double humi = ((double)((buff[3] << 8) | buff[4])) / ((1 << 16) - 1);
   uint16_t humi = (buff[3] << 8) | buff[4];
 
   prst_shtc3_read_t ret = {.temp_millicelcius = temp_c * 1000,
                            .humidity = humi};
+#if PRST_SHT3C_DEBUG
+  NRF_LOG_INFO("[sht3c] Read temp: " NRF_LOG_FLOAT_MARKER " oC",
+               NRF_LOG_FLOAT((float)temp_humi.temp_millicelcius / 1000.0));
+  NRF_LOG_INFO("[sht3c] Read humi: " NRF_LOG_FLOAT_MARKER " %%",
+               NRF_LOG_FLOAT(100.0 * temp_humi.humidity / (1 << 16)));
+#endif
   return ret;
 }