rfivet/stm32bringup
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Fix DHT11 temperature calculation for temperature below 0°C.

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This commit is contained in:
Renaud 2025-02-04 13:20:11 +08:00
parent efd5cd28c7
commit 6f4e46a36f
4 changed files with 17 additions and 20 deletions
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14
dht11.c
View File

@ -1,5 +1,5 @@
/* dht11.c -- DHT11 humidity and temperature sensor reading */ /* dht11.c -- DHT11 humidity and temperature sensor reading */
/* Copyright (c) 2020-2021 Renaud Fivet */ /* Copyright (c) 2020-2025 Renaud Fivet */
#include "dht11.h" /* implements DHT11 API */ #include "dht11.h" /* implements DHT11 API */
@ -25,7 +25,7 @@
unsigned char dht11_humid ; /* 5 .. 95 %RH */ unsigned char dht11_humid ; /* 5 .. 95 %RH */
signed char dht11_tempc ; /* -20 .. 60 C */ signed char dht11_tempc ; /* -20 .. 60 C */
unsigned char dht11_tempf ; /* .0 .. .9 C */ unsigned char dht11_tempf ; /* .0 .. .9 C */
int dht11_deciC ; /* -200 .. 600 */
void dht11_init( void) { void dht11_init( void) {
/* At startup A13 is ALT DIO with Pull Up enabled */ /* At startup A13 is ALT DIO with Pull Up enabled */
@ -79,14 +79,12 @@ dht11_retv_t dht11_read( void) {
dht11_tempc = values[ 2] ; dht11_tempc = values[ 2] ;
dht11_tempf = values[ 3] ; dht11_tempf = values[ 3] ;
if( dht11_tempf & 0x80) { if( dht11_tempf & 0x80) {
dht11_tempc *= -1 ; dht11_tempc = -( dht11_tempc + 1) ;
dht11_tempf = 10 - ( dht11_tempf & 0x7F) ; dht11_tempf ^= 0x80 ;
if( dht11_tempf == 10) {
dht11_tempc -= 1 ;
dht11_tempf = 0 ;
}
} }
dht11_deciC = dht11_tempc * 10 + dht11_tempf ;
return DHT11_SUCCESS ; return DHT11_SUCCESS ;
} }

5
dht11.h
View File

@ -1,5 +1,5 @@
/* dht11.h -- DHT11 API */ /* dht11.h -- DHT11 API */
/* Copyright (c) 2020 Renaud Fivet */ /* Copyright (c) 2020-2025 Renaud Fivet */
typedef enum { typedef enum {
DHT11_SUCCESS, DHT11_SUCCESS,
@ -12,6 +12,7 @@ typedef enum {
extern unsigned char dht11_humid ; /* 5 .. 95 %RH */ extern unsigned char dht11_humid ; /* 5 .. 95 %RH */
extern signed char dht11_tempc ; /* -20 .. 60 C */ extern signed char dht11_tempc ; /* -20 .. 60 C */
extern unsigned char dht11_tempf ; /* .0 .. .9 C */ extern unsigned char dht11_tempf ; /* .0 .. .9 C */
extern int dht11_deciC ; /* -200 .. 600 */
void dht11_init( void) ; void dht11_init( void) ;

6
dht11main.c
View File

@ -1,5 +1,5 @@
/* dht11main.c -- sample DHT11 sensor */ /* dht11main.c -- sample DHT11 sensor */
/* Copyright (c) 2020-2023 Renaud Fivet */ /* Copyright (c) 2020-2025 Renaud Fivet */
#include <stdio.h> #include <stdio.h>
#include "system.h" #include "system.h"
@ -17,8 +17,8 @@ int main( void) {
if( 2 == (last % 5)) /* every 5 seconds starting 2s after boot */ if( 2 == (last % 5)) /* every 5 seconds starting 2s after boot */
switch( dht11_read()) { switch( dht11_read()) {
case DHT11_SUCCESS: case DHT11_SUCCESS:
printf( "%u%%RH, %d.%uC\n", dht11_humid, dht11_tempc, printf( "%u%%RH, %d.%uC, %d\n", dht11_humid, dht11_tempc,
dht11_tempf) ; dht11_tempf, dht11_deciC) ;
break ; break ;
case DHT11_FAIL_TOUT: case DHT11_FAIL_TOUT:
puts( "Timeout") ; puts( "Timeout") ;

12
docs/32_errata.html
View File

@ -196,13 +196,11 @@ And retest after the following modification.
dht11_tempc = values[ 2] ; dht11_tempc = values[ 2] ;
dht11_tempf = values[ 3] ; dht11_tempf = values[ 3] ;
if( dht11_tempf & 0x80) { if( dht11_tempf & 0x80) {
dht11_tempc *= -1 ; dht11_tempc = -( dht11_tempc + 1) ;
dht11_tempf = 10 - ( dht11_tempf & 0x7F) ; dht11_tempf ^= 0x80 ;
if( dht11_tempf == 10) {
dht11_tempc -= 1 ;
dht11_tempf = 0 ;
}
} }
dht11_deciC = dht11_tempc * 10 + dht11_tempf ;
</pre> </pre>
<h2>Stability</h2> <h2>Stability</h2>
@ -239,6 +237,6 @@ or how bad the measurements are.
<a href="33_ds18b20.html">Next</a>, I will use another digital thermometer as a <a href="33_ds18b20.html">Next</a>, I will use another digital thermometer as a
reference. reference.
<hr>© 2020-2024 Renaud Fivet <hr>© 2020-2025 Renaud Fivet
</body> </body>
</html> </html>