Fix SVM40-Uart driver

- Add convenience methods
- Add some more explanations how to setup the sensor with arduino in readme

Author: Rol-la

README.md

@@ -28,14 +28,15 @@ Note: Installation via the Arduino Library Manager is coming soon.
 # Quick Start
 
 1. Connect the SVM40 Sensor to one of your Arduino board's
-   UART buses. We recommend using `Serial1`. Check the pinout of your Arduino
-   board to find the correct pins. The pinout of the SVM40
+   UART buses. You will need an Arduino board that has more than one UART since one instance is used for programming and tracing. We recommend using `Serial1`. Check the pinout of your Arduino board to find the correct pins. The pinout of the SVM40
    Sensor board can be found in the data sheet.
 
-	* **VDD** of the SEK-SVM40 to the **3.3V** of your Arduino board (5V works as well)
-	* **GND** of the SEK-SVM40 to the **GND** of your Arduino board
-	* **RX** of the SEK-SVM40 to the **UART1-TX** of your Arduino board
-	* **TX** of the SEK-SVM40 to the **UART1-RX** of your Arduino board
+	* **VDD** (pin 1) of the SEK-SVM40 to the **3.3V** of your Arduino board (5V works as well) 
+	* **GND** (pin 2) of the SEK-SVM40 to the **GND** of your Arduino board 
+	* **RX** (pin 3, host TX) of the SEK-SVM40 to the **UART1-TX** of your Arduino board 
+	* **TX** (pin 4, host RX) of the SEK-SVM40 to the **UART1-RX** of your Arduino board 
+
+	For use with UART **SEL** (pin 5 of SEK-SVM40 connector) must be floating!
 
 2. Open the `exampleUsage` sample project within the Arduino IDE
 

examples/exampleUsage/exampleUsage.ino

@@ -71,7 +71,7 @@ void setup() {
         errorToString(error, errorMessage, 256);
         Serial.println(errorMessage);
     } else {
-        Serial.print("SerialNumber:");
+        Serial.print("SerialNumber: ");
         Serial.println((char*)serialNumber);
     }
 
@@ -83,7 +83,7 @@ void setup() {
         errorToString(error, errorMessage, 256);
         Serial.println(errorMessage);
     } else {
-        Serial.print("ProductType:");
+        Serial.print("ProductType: ");
         Serial.println((char*)productType);
     }
 
@@ -95,7 +95,7 @@ void setup() {
         errorToString(error, errorMessage, 256);
         Serial.println(errorMessage);
     } else {
-        Serial.print("ProductName:");
+        Serial.print("ProductName: ");
         Serial.println((char*)productName);
     }
 
@@ -130,6 +130,26 @@ void setup() {
         Serial.println(protocolMinor);
     }
 
+    error = svm40.setTemperatureOffsetForRhtMeasurements(0);
+    if (error) {
+        Serial.print("Error trying to execute "
+                     "setTemperatureOffsetForRhtMeasurements(): ");
+        errorToString(error, errorMessage, 256);
+        Serial.println(errorMessage);
+    }
+
+    float tOffset;
+    error = svm40.getTemperatureOffsetForRhtMeasurements(tOffset);
+    if (error) {
+        Serial.print("Error trying to execute "
+                     "getTemperatureOffsetForRhtMeasurements(): ");
+        errorToString(error, errorMessage, 256);
+        Serial.println(errorMessage);
+    } else {
+        Serial.print("Temperature Offset: ");
+        Serial.println(tOffset);
+    }
+
     // Start Measurement
     error = svm40.startContinuousMeasurement();
     if (error) {
@@ -144,24 +164,22 @@ void loop() {
     char errorMessage[256];
     delay(1000);
 
-    // Read Measurement
-    int16_t vocIndex;
-    int16_t humidity;
-    int16_t temperature;
-    error = svm40.readMeasuredValuesAsIntegers(vocIndex, humidity, temperature);
+    float vocIndex;
+    float humidity;
+    float temperature;
+    error = svm40.readMeasuredValues(vocIndex, humidity, temperature);
     if (error) {
-        Serial.print(
-            "Error trying to execute readMeasuredValuesAsIntegers(): ");
+        Serial.print("Error trying to execute readMeasuredValues: ");
         errorToString(error, errorMessage, 256);
         Serial.println(errorMessage);
     } else {
-        Serial.print("VocIndex:");
-        Serial.print(vocIndex / 10.0);
+        Serial.print("VocIndex: ");
+        Serial.print(vocIndex);
         Serial.print("\t");
-        Serial.print("Humidity:");
-        Serial.print(humidity / 100.0);
+        Serial.print("Humidity: ");
+        Serial.print(humidity);
         Serial.print("\t");
-        Serial.print("Temperature:");
-        Serial.println(temperature / 200.0);
+        Serial.print("Temperature: ");
+        Serial.println(temperature);
     }
 }

src/SensirionUartSvm40.cpp

@@ -35,10 +35,10 @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */
-
 #include "SensirionUartSvm40.h"
 #include "Arduino.h"
 #include "SensirionCore.h"
+#include <math.h>
 
 #define SVM40_UART_ADDRESS 0x00
 
@@ -142,12 +142,31 @@ uint16_t SensirionUartSvm40::readMeasuredValuesAsIntegersWithRawParameters(
     return error;
 }
 
-uint16_t SensirionUartSvm40::getTemperatureOffsetForRhtMeasurements(
-    uint8_t tOffset[], uint8_t tOffsetSize) {
+uint16_t SensirionUartSvm40::readMeasuredValues(float& vocIndex,
+                                                float& humidity,
+                                                float& temperature) {
     uint16_t error;
-    uint8_t buffer[522];
-    SensirionShdlcTxFrame txFrame(buffer, 522);
-    SensirionShdlcRxFrame rxFrame(buffer, 522);
+    int16_t humidityRaw;
+    int16_t temperatureRaw;
+    int16_t vocRaw;
+
+    error = readMeasuredValuesAsIntegers(vocRaw, humidityRaw, temperatureRaw);
+    if (error) {
+        return error;
+    }
+
+    humidity = static_cast<float>(humidityRaw) / 100.0f;
+    temperature = static_cast<float>(temperatureRaw) / 200.0f;
+    vocIndex = static_cast<float>(vocRaw) / 10.0f;
+    return NoError;
+}
+
+uint16_t SensirionUartSvm40::getTemperatureOffsetForRhtMeasurementsRaw(
+    int16_t& tOffset) {
+    uint16_t error;
+    uint8_t buffer[20];
+    SensirionShdlcTxFrame txFrame(buffer, sizeof buffer);
+    SensirionShdlcRxFrame rxFrame(buffer, sizeof buffer);
 
     error = txFrame.begin(0x60, SVM40_UART_ADDRESS, 1);
     error |= txFrame.addUInt8(0x01);
@@ -162,10 +181,27 @@ uint16_t SensirionUartSvm40::getTemperatureOffsetForRhtMeasurements(
         return error;
     }
 
-    error |= rxFrame.getBytes(tOffset, tOffsetSize);
+    error |= rxFrame.getInt16(tOffset);
     return error;
 }
 
+uint16_t
+SensirionUartSvm40::getTemperatureOffsetForRhtMeasurements(float& tOffset) {
+    uint16_t error;
+    int16_t tOffsetRaw;
+
+    tOffset = NAN;
+
+    error = getTemperatureOffsetForRhtMeasurementsRaw(tOffsetRaw);
+
+    if (error) {
+        return error;
+    }
+
+    tOffset = static_cast<float>(tOffsetRaw) / 200.0f;
+    return NoError;
+}
+
 uint16_t SensirionUartSvm40::getVocTuningParameters(
     int16_t& vocIndexOffset, int16_t& learningTimeHours,
     int16_t& gatingMaxDurationMinutes, int16_t& stdInitial) {
@@ -213,16 +249,16 @@ uint16_t SensirionUartSvm40::storeNvData() {
     return error;
 }
 
-uint16_t SensirionUartSvm40::setTemperatureOffsetForRhtMeasurements(
-    uint8_t tOffset[], uint8_t tOffsetSize) {
+uint16_t
+SensirionUartSvm40::setTemperatureOffsetForRhtMeasurementsRaw(int16_t tOffset) {
     uint16_t error;
-    uint8_t buffer[520];
-    SensirionShdlcTxFrame txFrame(buffer, 520);
-    SensirionShdlcRxFrame rxFrame(buffer, 520);
+    uint8_t buffer[16];
+    SensirionShdlcTxFrame txFrame(buffer, sizeof buffer);
+    SensirionShdlcRxFrame rxFrame(buffer, sizeof buffer);
 
-    error = txFrame.begin(0x60, SVM40_UART_ADDRESS, 255);
+    error = txFrame.begin(0x60, SVM40_UART_ADDRESS, 3);
     error |= txFrame.addUInt8(0x81);
-    error |= txFrame.addBytes(tOffset, tOffsetSize);
+    error |= txFrame.addInt16(tOffset);
     error |= txFrame.finish();
     if (error) {
         return error;
@@ -234,6 +270,12 @@ uint16_t SensirionUartSvm40::setTemperatureOffsetForRhtMeasurements(
     return error;
 }
 
+uint16_t
+SensirionUartSvm40::setTemperatureOffsetForRhtMeasurements(float tOffset) {
+    int16_t tOffsetRaw = static_cast<int16_t>(tOffset * 200.0f);
+    return setTemperatureOffsetForRhtMeasurementsRaw(tOffsetRaw);
+}
+
 uint16_t SensirionUartSvm40::setVocTuningParameters(
     int16_t vocIndexOffset, int16_t learningTimeHours,
     int16_t gatingMaxDurationMinutes, int16_t stdInitial) {

src/SensirionUartSvm40.h

@@ -96,6 +96,26 @@ class SensirionUartSvm40 {
     uint16_t readMeasuredValuesAsIntegers(int16_t& vocIndex, int16_t& humidity,
                                           int16_t& temperature);
 
+    /**
+     * readMeasuredValues() - Returns the new measurement results.
+     *
+     * @note This command is only available in measurement mode. The firmware
+     * updates the measurement values every second. Polling data with a faster
+     * sampling rate will return the same values. The first measurement is
+     * available 1 second after the start measurement command is issued. Any
+     * readout prior to this will return zero initialized values.
+     *
+     * @param vocIndex VOC index.
+     *
+     * @param humidity Compensated ambient humidity in % RH.
+     *
+     * @param temperature Compensated ambient temperature in degrees celsius.
+     *
+     * @return 0 on success, an error code otherwise
+     */
+    uint16_t readMeasuredValues(float& vocIndex, float& humidity,
+                                float& temperature);
+
     /**
      * readMeasuredValuesAsIntegersWithRawParameters() - Returns the new
      * measurement results as integers with raw values added.
@@ -140,8 +160,20 @@ class SensirionUartSvm40 {
      *
      * @return 0 on success, an error code otherwise
      */
-    uint16_t getTemperatureOffsetForRhtMeasurements(uint8_t tOffset[],
-                                                    uint8_t tOffsetSize);
+    uint16_t getTemperatureOffsetForRhtMeasurementsRaw(int16_t& tOffset);
+
+    /**
+     * getTemperatureOffsetForRhtMeasurements() - Gets the T-Offset for the
+     * temperature compensation of the RHT algorithm.
+     *
+     * @param tOffset Temperature offset which is used for the RHT measurements
+     * in degrees celsius with no scaling.
+     *
+     * @note Only supported for firmware version >= 2.0.
+     *
+     * @return 0 on success, an error code otherwise
+     */
+    uint16_t getTemperatureOffsetForRhtMeasurements(float& tOffset);
 
     /**
      * getVocTuningParameters() - Gets the currently set parameters for
@@ -192,8 +224,21 @@ class SensirionUartSvm40 {
      *
      * @return 0 on success, an error code otherwise
      */
-    uint16_t setTemperatureOffsetForRhtMeasurements(uint8_t tOffset[],
-                                                    uint8_t tOffsetSize);
+    uint16_t setTemperatureOffsetForRhtMeasurementsRaw(int16_t tOffset);
+
+    /**
+     * setTemperatureOffsetForRhtMeasurements() - Sets the T-Offset for the
+     * temperature compensation of the RHT algorithm.
+     *
+     * @note Execute the store command after writing the parameter to store it
+     * in the non-volatile memory of the device otherwise the parameter will be
+     * reset upton a device reset.
+     *
+     * @param tOffset Temperature offset in degrees celsius.
+     *
+     * @return 0 on success, an error code otherwise
+     */
+    uint16_t setTemperatureOffsetForRhtMeasurements(float tOffset);
 
     /**
      * setVocTuningParameters() - Sets parameters to customize the VOC