add resetSensor() (#7)

* add resetSensor() * stabilize readStatus() * add examples * improve comments in code * update readme.md
RobTillaart · Sep 18, 2022 · 2fc2c11 · 2fc2c11
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diff --git a/DHT20.cpp b/DHT20.cpp
@@ -1,7 +1,7 @@
 //
 //    FILE: DHT20.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.3
+// VERSION: 0.1.4
 // PURPOSE: Arduino library for DHT20 I2C temperature and humidity sensor.
 //
 // HISTORY:
@@ -12,15 +12,21 @@
 //                      fix keywords
 //                      add readStatus()  fix _readStatus()
 //                      add setWireTimeout(250000, true);  // in comments
-//  0.1.3   2022-09-xx  add wrapper status functions
+//  0.1.3   2022-09-17  add wrapper status functions
 //                      improve performance read()
 //                      refactor, update readme.md
+//  0.1.4   2022-09-18  add resetSensor() code.
+//                      add comments in .h file
+//                      add examples
+//                      stabilize readStatus()
+//                      update readme.md
 
 
 #include "DHT20.h"
 
 
 //  set DHT20_WIRE_TIME_OUT to 0 to disable.
+//  note this timeout is commented in code below.
 #define DHT20_WIRE_TIME_OUT         250000    //  microseconds
 
 const uint8_t DHT20_ADDRESS = 0x38;
@@ -71,6 +77,23 @@ bool DHT20::isConnected()
 }
 
 
+//  See datasheet 7.4 Sensor Reading Process, point 1
+//  use with care.
+uint8_t DHT20::resetSensor()
+{
+  uint8_t count = 255;
+  if ((readStatus() & 0x18) != 0x18)
+  {
+    count++;
+    if (_resetRegister(0x1B)) count++;
+    if (_resetRegister(0x1C)) count++;
+    if (_resetRegister(0x1E)) count++;
+    delay(10);
+  }
+  return count;
+}
+
+
 ////////////////////////////////////////////////
 //
 //  READ THE SENSOR
@@ -89,7 +112,6 @@ int DHT20::read()
   while (isMeasuring())
   {
     yield();
-    delay(1);
   }
   //  read the measurement
   status = readData();
@@ -218,7 +240,9 @@ uint8_t DHT20::readStatus()
   _wire->beginTransmission(DHT20_ADDRESS);
   _wire->write(0x71);
   _wire->endTransmission();
+  delay(1);  //  needed to stabilize timing
   _wire->requestFrom(DHT20_ADDRESS, (uint8_t)1);
+  delay(1);  //  needed to stabilize timing
   return (uint8_t) _wire->read();
 }
 
@@ -249,7 +273,7 @@ int DHT20::internalStatus()
 
 ////////////////////////////////////////////////
 //
-//  OTHER
+//  TIMING
 //
 uint32_t DHT20::lastRead()
 {
@@ -290,5 +314,40 @@ uint8_t DHT20::_crc8(uint8_t *ptr, uint8_t len)
 }
 
 
+//  Code based on demo code sent by www.aosong.com
+//  no further documentation.
+//  0x1B returned 18, 0, 4
+//  0x1C returned 18, 65, 0
+//  0x1E returned 18, 8, 0
+//    18 seems to be status register
+//    other values unknown.
+bool DHT20::_resetRegister(uint8_t reg)
+{
+  uint8_t value[3];
+  _wire->beginTransmission(DHT20_ADDRESS);
+  _wire->write(reg);
+  _wire->write(0x00);
+  _wire->write(0x00);
+  if (_wire->endTransmission() != 0) return false;
+  delay(5);
+
+  int bytes = _wire->requestFrom(DHT20_ADDRESS, 3); 
+  for (int i = 0; i < bytes; i++)
+  {
+    value[i] = _wire->read();
+    //  Serial.println(value[i], HEX);
+  }
+  delay(10);
+
+  _wire->beginTransmission(DHT20_ADDRESS);
+  _wire->write(0xB0 | reg);
+  _wire->write(value[1]);
+  _wire->write(value[2]);
+  if (_wire->endTransmission() != 0) return false;
+  delay(5);
+  return true;
+}
+
+
 // -- END OF FILE --
 
diff --git a/DHT20.h b/DHT20.h
@@ -3,7 +3,7 @@
 //    FILE: DHT20.h
 //  AUTHOR: Rob Tillaart
 // PURPOSE: Arduino library for DHT20 I2C temperature and humidity sensor.
-// VERSION: 0.1.3
+// VERSION: 0.1.4
 // HISTORY: See DHT20.cpp
 //     URL: https://github.com/RobTillaart/DHT20
 //
@@ -21,7 +21,7 @@
 #include "Arduino.h"
 #include "Wire.h"
 
-#define DHT20_LIB_VERSION                    (F("0.1.3"))
+#define DHT20_LIB_VERSION                    (F("0.1.4"))
 
 #define DHT20_OK                             0
 #define DHT20_ERROR_CHECKSUM                -10
@@ -32,48 +32,71 @@
 #define DHT20_ERROR_LASTREAD                -15
 
 
-#define DHT20_ACQUISITION_TIME               85
-
-
 class DHT20
 {
 public:
-  DHT20(TwoWire *wire = &Wire);        // to be tested explicitly
+  //  CONSTRUCTOR
+  //  fixed address 0x38
+  DHT20(TwoWire *wire = &Wire);
 
+  //  start the I2C
 #if defined(ESP8266) || defined(ESP32)
   bool     begin(const uint8_t dataPin, const uint8_t clockPin);
 #endif
   bool     begin();
   bool     isConnected();
 
+
   //  ASYNCHRONUOUS CALL
+  //  trigger acquisition.
   int      requestData();
+  //  read the raw data.
   int      readData();
+  //  converts raw databits to temperature and humidity.
   int      convert();
 
+
   //  SYNCHRONUOUS CALL
+  //  blocking read call to read + convert data
   int      read();
+  //  access the converted temperature & humidity
   float    getHumidity();
   float    getTemperature();
 
-  //  CALIBRATION  1st order
+
+  //  OFFSET  1st order adjustments
   void     setHumOffset(float offset);
   void     setTempOffset(float offset);
   float    getHumOffset();
   float    getTempOffset();
 
+
   //  READ STATUS
   uint8_t  readStatus();
+  //  3 wrapper functions around readStatus()
   bool     isCalibrated();
   bool     isMeasuring();
   bool     isIdle();
+  //  status from last read()
   int      internalStatus();
 
-  //  OTHER
+
+  //  TIMING
   uint32_t lastRead();
   uint32_t lastRequest();
 
 
+  //  RESET  (new since 0.1.4)
+  //  use with care 
+  //  returns number of registers reset => must be 3
+  //  3     = OK
+  //  0,1,2 = error.
+  //  255   = no reset needed.
+  //  See datasheet 7.4 Sensor Reading Process, point 1
+  //  use with care 
+  uint8_t  resetSensor();
+
+
 private:
   float    _humidity;
   float    _temperature;
@@ -87,6 +110,9 @@ class DHT20
 
   uint8_t  _crc8(uint8_t *ptr, uint8_t len);
 
+  //  use with care
+  bool     _resetRegister(uint8_t reg);
+
   TwoWire* _wire;
 };
 

diff --git a/README.md b/README.md
@@ -23,10 +23,11 @@ Calling these latter again will return the same values until a new **read()** is
 The **read()** call of this sensor is blocking for 80+ milliseconds (datasheet 7.4)
 so the library also has a asynchronous interface. See below.
 
-Verified to work with Arduino UNO and ESP32.
+Since 0.1.3 and 0.1.4 the performance of **read()** has been optimized, 
+still blocking but less long for about 45 milliseconds.
 
 
-## Connection
+### Connection
 
 Always check datasheet 
 
@@ -40,9 +41,10 @@ Front view
           +--------------+
 ```
 
-## Tested
+### Tested
 
-Examples verified to work with Arduino UNO and ESP32.
+Verified to work with Arduino UNO and ESP32.
+Please let me know if other platforms work (or not).
 
 
 ## Interface
@@ -74,17 +76,15 @@ It returns the status of the read which should be 0.
 
 ### Asynchronous interface
 
-Note the async interface is not 100% functional yet. 
-Expect functional complete in 0.2.0.
-
 There are two timings that need to be considdered, 
 - time between requests = 1000 ms
-- time between request and data ready.
+- time between request and data ready = 80 ms
 
-The async interface allows one to continue processing whatever after a **requestData()** has been made. Note that there should be at least **1000 milliseconds** between subsequent requests.
+The async interface allows one to continue processing after a **requestData()** has been made. 
+Note that there should be at least **1000 milliseconds** between subsequent requests.
 
-After **DHT20_ACQUISITION_TIME == 85 ms** enough time after the request has 
-passed to read the data of the measurement. So the sensor can be read with **readData()**.
+With **bool isMeasuring()** one can check if a new measurement is ready.
+If so the sensor can be read with **readData()**.
 
 To interpret the read bits to temperature, humidity and status one needs to call **convert()** as last step.
 
@@ -100,19 +100,31 @@ See the example **DHT20_async.ino**
 ### Status
 
 - **uint8_t readStatus()** forced read of the status only.
+This function blocks a few milliseconds to optimize communication.
 - **bool isCalibrated()** idem, wrapper around **readStatus()**
 - **bool isMeasuring()** idem, wrapper around **readStatus()**
 - **bool isIdle()** idem, wrapper around **readStatus()**
-- **int internalStatus()** returns the internal status of the sensor. (debug ).
+- **int internalStatus()** returns the internal status of the sensor. (for debug).
 
 |  status bit  |  meaning                   |
 |:------------:|:---------------------------|
-|    7         |  busy making measurement   |
+|    7         |  1 = measurement, 0 = idle |
 |  6 - 4       |  unknown                   |
-|    3         |  1 = calibrated, 0 is not  |
+|    3         |  1 = calibrated, 0 = not   |
 |  2 - 0       |  unknown                   |
 
 
+#### Experimental 0.1.4 resetSensor
+
+Use with care, as this is not tested.
+
+- **uint8_t resetSensor()** if at startup the sensor does not return a status of 0x18, 
+three registers 0x1B, 0x1C and 0x1E need to be reset. 
+See datasheet 7.4 Sensor Reading Process, point 1.
+There is no documentation about the meaning of these registers.
+The code is based upon example code for the AHT20 (from manufacturer).
+
+
 ### Timing
 
 - **uint32_t lastRead()** last time the sensor is read in milliseconds since start.
@@ -129,7 +141,7 @@ See the example **DHT20_async.ino**
 | DHT20_MISSING_BYTES         |   -12   |  check connection
 | DHT20_ERROR_BYTES_ALL_ZERO  |   -13   |  check connection
 | DHT20_ERROR_READ_TIMEOUT    |   -14   |
-| DHT20_ERROR_LASTREAD        |   -15   |
+| DHT20_ERROR_LASTREAD        |   -15   |  wait 1 second between reads
 
 
 ## Operation
@@ -141,26 +153,24 @@ See examples
 
 #### must
 
-- update documentation
-- comments in .h file
 
 #### should
 
-- add examples
-- check TODO's in code.
-
 
 #### could
 
 - improve unit tests.
 - investigate 
   - sensor calibration (website aosong?)
-
+- investigate optimizing timing in readStatus()
+  - delay(1) ==> microSeconds(???).
+- separate changelog.md
+- connected flag?
 
 #### won't
 
 - **void setIgnoreChecksum(bool = false)** ignore checksum flag speeds up communication a bit
-- **bool getIgnoreChecksum()** get status. for completeness.
+- **bool getIgnoreChecksum()** get checksum flag. for completeness.
 - 
 
 
diff --git a/examples/DHT20/DHT20.ino b/examples/DHT20/DHT20.ino
@@ -32,9 +32,7 @@ void setup()
   Serial.println(DHT20_LIB_VERSION);
   Serial.println();
 
-  delay(2000);
-
-
+  delay(1000);
 }
 
 

diff --git a/examples/DHT20/performance_0.1.2.txt b/examples/DHT20/performance_0.1.2.txt
@@ -1,6 +1,8 @@
 ...Arduino\libraries\DHT20\examples\DHT20\DHT20.ino
 DHT20 LIBRARY VERSION: 0.1.2
 
+IDE 1.8.19
+Arduino UNO
 
 Type	Humidity (%)	Temp (°C)	Time (µs)	Status
 DHT20 	70.8		21.4		86701		OK

diff --git a/examples/DHT20/performance_0.1.3.txt b/examples/DHT20/performance_0.1.3.txt
@@ -1,6 +1,8 @@
 ...Arduino\libraries\DHT20\examples\DHT20\DHT20.ino
 DHT20 LIBRARY VERSION: 0.1.3
 
+IDE 1.8.19
+Arduino UNO
 
 Type	Humidity (%)	Temp (°C)	Time (µs)	Status
 DHT20 	61.4		21.5		54684		OK