main.cpp

00001 /* Test ability to read SHT75 sensor from F303K8 board.
00002 
00003   Note:  Can not be on same pins as I2C due to different pull up 
00004   requirements.
00005 
00006   By Joseph Ellsworth CTO of A2WH
00007   Take a look at A2WH.com Producing Water from Air using Solar Energy
00008   March-2016 License: https://developer.mbed.org/handbook/MIT-Licence
00009   Please contact us http://a2wh.com for help with custom design projects.
00010   
00011   Sample code to test SHT75 humidity sensor using STM F303K8 board.    
00012   Uses a 3.3V from board to power sensor.  10K resistor Pull-up on data.   
00013   Must not be on same pins as I2C.    Uses D0 for Clk and D1 for Data.
00014 
00015   I had to modify sample code supplied by https://developer.mbed.org/users/nimbusgb/code/SHT75/  
00016   because the sensor failed to read without the softReset() and readStatus() at beginning 
00017   of measurement loop.  I think this is caused by the 72Mhtz speed of the F303K8  but did 
00018   not attempt to fully diagnose.
00019 
00020   The readStatus() method from library seems to malfunction and always return a -1 
00021   which never changes even when sensor is unplugged. 
00022 
00023   
00024  */
00025 
00026 #include "mbed.h"
00027 #include <stdint.h>
00028 
00029 #define sht75_clk D0
00030 #define sht75_data D1
00031 #include "sht7X.h" 
00032 SHT75 sht(sht75_clk, sht75_data); 
00033  
00034 
00035 // Host PC Communication channels
00036 Serial pc(USBTX, USBRX); // tx, rx
00037 char buff[100];
00038 
00039 DigitalOut myled(LED1);
00040 
00041 int main()
00042 {
00043     pc.baud(38400);
00044     wait(1);
00045     while(1) {
00046         myled = !myled;
00047         float temperature;                    // temperature -40 to 120 deg C
00048         float humidity;                       // relative humidity 1% to 100%
00049         float humi_f,rh_lin,rh_true;          // working registers for Illustration purposes
00050         int t;                                // temporary store for the temp ticks
00051         int h;
00052         sht.softReset();        
00053         int stat = sht.readStatus();
00054         wait(3.0);
00055         sht.readTempTicks(&t);
00056         temperature = ((float)(t) * 0.01) - 39.61;
00057 
00058         sht.readHumidityTicks(&h);
00059         humi_f = (float)(h);
00060         rh_lin = C3 * humi_f * humi_f + C2 * humi_f + C1;
00061         rh_true=(((temperature/100)-25)*(T1+T2*humi_f)+rh_lin);
00062         if(rh_true>100)rh_true=100;                             //cut if the value is outside
00063         if(rh_true<1)rh_true=1;                                 //the physical possible range
00064         humidity = rh_true;
00065         pc.printf("stat=%d Temp: %2.2f RH %2.2f\n\r",stat, temperature, humidity);
00066         
00067         wait(3.0);
00068     }
00069 }