Revision 1:c7a36fa2c772, committed 2017-09-29

Comitter:

kohacraft

Date:

Fri Sep 29 03:15:40 2017 +0000

Parent:

0:963c0badad70

Commit message:

bug fixed

Changed in this revision

--- a/main.cpp	Wed Sep 27 06:51:22 2017 +0000
+++ b/main.cpp	Fri Sep 29 03:15:40 2017 +0000
@@ -1,42 +1,79 @@
-#include "mbed.h"
-#include "SoftSerial.h"
+/* 
+ Read from MH-Z19 CO2 Sensor by serial
+ and show data to PC throw the softserial
+ for LPC1114FN28
+ 
+ MH-Z19B Datasheet http://www.winsen-sensor.com/d/files/infrared-gas-sensor/mh-z19b-co2-ver1_0.pdf
+ Also reference https://github.com/nara256/mhz19_uart
+ 
+ please see the blog in detail
+ http://kohacraft.com/archives/1068007971.html
+ 
+*/
 
-SoftSerial softSerial(dp18,dp17); //Tx,Rx
-Serial pc(USBTX, USBRX); //Tx,Rx
+#include "mbed.h"
+#include "SoftSerial.h" // by Erick Olieman https://os.mbed.com/users/Sissors/code/SoftSerial/
+
+SoftSerial pc(dp18,dp17); //Tx,Rx to USB serial (mbed cat)
+Serial co2sensor(USBTX, USBRX); //Tx,Rx to mh-z19 CO2 sensor
 
 int main() {
     
-    softSerial.baud(9600);  //to mbed cat
-    pc.baud(9600);  // to mh-z19 CO2 sensor
+    pc.baud(9600);
+    co2sensor.baud(9600); 
     
     char command[] = { 0xff , 0x01 , 0x86 , 0 , 0 , 0 , 0 , 0 , 0x79 }; //command of Read CO2 concentration
     char responds[9];
     
-    unsigned char c;
     
-    if( pc.readable() ) // throw received data away
-        responds[0] = pc.getc(  );
-    
+    while( co2sensor.readable() ) // throw received data away
+        responds[0] = co2sensor.getc();
+    while( pc.readable() ) // throw received data away
+        responds[0] = pc.getc();
+        
+    long time=0;
+   
     while(1) {
         
         //send command
         for( int i=0 ; i<9 ; i++ ) {
-            while( pc.writeable() == 0 );
-            pc.putc( command[i] );
+            while( co2sensor.writeable() == 0 );   //wait for writable a data
+            co2sensor.putc( command[i] );
         }
         
         //receve responds
-        c=0;    //calc check sum
-        softSerial.printf(" responds:");
-        for( int i=0 ; i<9 ; i++ ) {
-            responds[i] = pc.getc(  );
-            softSerial.printf("%x ",responds[i]);
-            c += responds[i];
+        unsigned char csm=0;    //clear check sum
+        for( int i=0 ; i<9 ; i++ )  //clear responds variable
+            responds[i] = 0;
+        pc.printf("responds:");
+        int i=0;
+        for( int timeout = 0 ; timeout < 10000 ; timeout++ ) {        
+
+            if( co2sensor.readable() ) {
+                responds[i] = co2sensor.getc(  );
+                pc.printf("%x ",responds[i]);
+            
+                if( responds[0] == 0xff ) {  // wether the first data is 0xff 
+                    // sdd check sum
+                    csm += responds[i];
+                    timeout = 0;
+                    i++;
+                    if( i>8 )
+                        break; // received all data
+                }
+            }
         }
-        c -= responds[8];
-        c = ( 0xff - c );
-        softSerial.printf(" csm:%x CO2:%dppm temp:%dC stat:%d\r" , c , responds[2]*256 + responds[3] , responds[4]-40 , responds[5]);
+        
+        //check the check sum and show to PC
+        csm -= responds[8];
+        csm = ( 0xff - csm );
+        if( responds[8] == csm ) {  // compare with check sum 
+            pc.printf("csm:%x CO2:%dppm temp:%dC stat:%d," , csm , responds[2]*256 + responds[3] , responds[4]-40 , responds[5]);
+            pc.printf("%d,%d,%d,%d\r" , time , responds[2]*256 + responds[3] , responds[4]-40 , responds[5]);
+        }
+        
         wait(1);
+        time++;
 
     }
 }