0.2.0 MHZCO2

Author: RobTillaart

libraries/MHZCO2/CHANGELOG.md

@@ -6,13 +6,20 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.2.0] - 2023-12-29
+- Fix #9 bug in **setPPM()**
+- fix race condition in **receive()**
+- update readme.md
+- minor edits
+
+----
+
 ## [0.1.4] - 2023-11-14
 - update readme.md
 - add plotter example (MEGA)
 - update keywords.
 - minor edits
 
-
 ## [0.1.3] - 2023-07-27
 - remove MTP40F as it is not compatible
 - update examples.

libraries/MHZCO2/MHZCO2.cpp

@@ -1,7 +1,7 @@
 //
 //    FILE: MHZCO2.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.4
+// VERSION: 0.2.0
 // PURPOSE: Arduino Library for MHZ series CO2 sensors
 //    DATE: 2020-05-05
 //     URL: https://github.com/RobTillaart/MHZCO2
@@ -38,7 +38,10 @@ void MHZCO2::setPPM(uint16_t PPM)
 {
   _PPM = PPM;
   uint8_t data[9] = {0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
-  data[8] = PPM >> 8;
+  //  as max value is lower than 65536 only two bytes need to be set.
+  //  data[4] = 0;
+  //  data[5[ = 0;
+  data[6] = PPM >> 8;
   data[7] = PPM & 0xFF;
   data[8] = checksum(data);
   send(data, 9);
@@ -137,23 +140,32 @@ void MHZCO2::calibrateAuto(bool mode)
 void MHZCO2::send(uint8_t * data, uint8_t len)
 {
   _str->write(data, len);
-  _str->flush();
+  _str->flush();  //  do not return until all data is sent.
 }
 
 
 int MHZCO2::receive(uint8_t * answer)
 {
   uint32_t start = millis();
-  while (_str->available() == 0)
-  {
-    if (millis() - start > 1000) return MHZCO2_TIMEOUT;
-  }
-  for (uint8_t i = 0; i < 9; i++)
+
+  //  need to read 9 bytes.
+  uint8_t i = 0;
+  while (i < 9)
   {
-    answer[i] = _str->read();
+    if (_str->available())
+    {
+      answer[i] = _str->read();
+      i++;
+    }
+    else
+    {
+      //  note: hardcoded timeout
+      if (millis() - start > 1000) return MHZCO2_TIMEOUT;
+    }
   }
   //  verify checksum
   if (answer[8] != checksum(answer)) return MHZCO2_ERROR_CRC;
+
   return MHZCO2_OK;
 }
 
@@ -170,15 +182,6 @@ uint8_t MHZCO2::checksum(uint8_t *arr)
 }
 
 
-/* slightly faster
-uint8_t MHZCO2::checksum(uint8_t *arr)
-{
-  uint8_t sum = 0xFF;
-  for (uint8_t i = 1; i < 8; i++) sum -= arr[i];
-  return sum + 1;
-}
-*/
-
 
 /////////////////////////////////////////////////////////
 //

libraries/MHZCO2/MHZCO2.h

@@ -2,15 +2,15 @@
 //
 //    FILE: MHZCO2.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.4
+// VERSION: 0.2.0
 // PURPOSE: Arduino Library for MHZ series CO2 sensors
 //    DATE: 2020-05-05
 //     URL: https://github.com/RobTillaart/MHZCO2
 //
 
 #include "Arduino.h"
 
-#define MHZCO2_LIB_VERSION        (F("0.1.4"))
+#define MHZCO2_LIB_VERSION        (F("0.2.0"))
 
 #define MHZCO2_OK                 0
 #define MHZCO2_TIMEOUT            -10
@@ -25,11 +25,13 @@ class MHZCO2
   void     begin(Stream * str);
   uint32_t uptime();
 
+
   //  PPM = 2000, 5000, 10000 (other values unknown)
   //  check datasheet
   void     setPPM(uint16_t PPM);
   uint16_t getPPM();
 
+
   //  MEASUREMENT
   int      measure();
   uint32_t lastMeasurement();
@@ -38,12 +40,14 @@ class MHZCO2
   int      getAccuracy();
   int      getMinCO2();
 
+
   //  CALIBRATION
   //  USE WITH CARE => READ DATASHEET!
   void     calibrateZero();
   void     calibrateSpan(uint16_t span);
   void     calibrateAuto(bool mode = true);
 
+
 protected:
   Stream * _str;
   uint32_t _startTime;
@@ -61,6 +65,7 @@ class MHZCO2
 };
 
 
+
 /////////////////////////////////////////////////////////
 //
 //  DERIVED CLASSES

libraries/MHZCO2/README.md

@@ -25,19 +25,34 @@ This might change in the future as compatibles might differ on detail.
 
 Reference: user manual MHZ129B 2019-04-25 version 1.4
 
+#### Version 0.2.0
+
+Version 0.2.0 fixes a bug in **setPPM()** which makes older versions obsolete.
+
+
 #### Compatibles
 
 This list is not verified although these devices should be compatible based upon datasheet.
 
+There exists different models of 400-2000 PPM and 400-5000 PPM and 400-10000 PPM. 
+As far as known these have the same interface as there is very little information to be found.
+
+
 |  type      | precision  |  notes  |
 |:-----------|:----------:|:--------|
 |  MHZ1311A  | 50ppm + 5% | energy saving version
 |  MHZ19     | 50ppm + 5% | 
 |  MHZ19B    | 50ppm + 3% | test device
-|  MHZ19C    | 50ppm + 5% | 
+|  MHZ19C    | 50ppm + 5% | (1)
 |  MHZ19D    | 50ppm + 5% | 
 |  MHZ19E    | 50ppm + 5% |
 
+Note (1):
+There exists different models of the MHZ19C and probably others. 
+The range can go from 400-2000 PPM, 400-5000 PPM and 400-10000 PPM. 
+As far as known these have the same interface as there is very little 
+information to be found. See #9.
+
 Note: The calibration of the MHZ1311A is different than MHZ19x series
 
 If there are compatible devices missing in this list, please let me know.
@@ -85,7 +100,8 @@ or a softwareSerial port.
 
 #### Measure
 
-- **int measure()** workhorse, send command to read the sensor.
+- **int measure()** workhorse, send command to read the sensor and 
+waits until an answer is received. Return values see below.
 - **uint32_t lastMeasurement()** timestamp in milliseconds of last measurement.
 - **int getCO2()** returns CO2 PPM last measurement.
 - **int getTemperature()** returns temperature last measurement.
@@ -94,6 +110,16 @@ or a softwareSerial port.
 
 The latter two might not be supported by all MH sensors.
 
+
+Return values of **measure()**
+
+|  value  |  Name              |  Description  |
+|:-------:|:------------------:|:--------------|
+|    0    |  MHZCO2_OK         | measurement succeeded.
+|   -10   |  MHZCO2_TIMEOUT    | to too long to receive an answer
+|   -11   |  MHZCO2_ERROR_CRC  | Checksum error, handle answer with care.
+
+
 #### Calibration
 
 **WARNING:** use with care, read the datasheet as these commands may disrupt your sensor.
@@ -118,7 +144,6 @@ See - https://keelingcurve.ucsd.edu/
 - improve documentation
 - buy hardware MHZ19B / MHZ19C
 - test with hardware
-- verify checksum
 - verify timeout
 
 
@@ -130,6 +155,8 @@ See - https://keelingcurve.ucsd.edu/
 
 #### Could
 
+- investigate configurable timeout. now hardcoded 1 second.
+  - 2 bytes + 2 functions.
 - extend unit tests
 - add type info for derived classes?
   - A .. E ?

libraries/MHZCO2/library.json

@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/MHZCO2.git"
   },
-  "version": "0.1.4",
+  "version": "0.2.0",
   "license": "MIT",
   "frameworks": "*",
   "platforms": "*",

libraries/MHZCO2/library.properties

@@ -1,5 +1,5 @@
 name=MHZCO2
-version=0.1.4
+version=0.2.0
 author=Rob Tillaart <[email protected]>
 maintainer=Rob Tillaart <[email protected]>
 sentence=Arduino Library for MHZ series CO2 sensors.