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Configurable pullup delay time, default 55 usec

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This commit is contained in:
Phillip Burgess 2019-02-14 09:24:17 -08:00
parent 1e752b12ee
commit 7cec0cb06d
3 changed files with 10 additions and 4 deletions
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9
DHT.cpp
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@ -22,7 +22,9 @@ DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
// based on the speed of the processor. // based on the speed of the processor.
} }
void DHT::begin(void) { // Optionally pass pull-up time (in microseconds) before DHT reading starts.
// Default is 55 (see function declaration in DHT.h).
void DHT::begin(uint8_t usec) {
// set up the pins! // set up the pins!
pinMode(_pin, INPUT_PULLUP); pinMode(_pin, INPUT_PULLUP);
// Using this value makes sure that millis() - lastreadtime will be // Using this value makes sure that millis() - lastreadtime will be
@ -30,6 +32,7 @@ void DHT::begin(void) {
// but so will the subtraction. // but so will the subtraction.
_lastreadtime = millis() - MIN_INTERVAL; _lastreadtime = millis() - MIN_INTERVAL;
DEBUG_PRINT("DHT max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC); DEBUG_PRINT("DHT max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC);
pullTime = usec;
} }
//boolean S == Scale. True == Fahrenheit; False == Celcius //boolean S == Scale. True == Fahrenheit; False == Celcius
@ -179,8 +182,10 @@ bool DHT::read(bool force) {
// End the start signal by setting data line high for 40 microseconds. // End the start signal by setting data line high for 40 microseconds.
pinMode(_pin, INPUT_PULLUP); pinMode(_pin, INPUT_PULLUP);
// Delay a moment to let sensor pull data line low.
delayMicroseconds(pullTime);
// Now start reading the data line to get the value from the DHT sensor. // Now start reading the data line to get the value from the DHT sensor.
delayMicroseconds(40); // Delay a bit to let sensor pull data line low.
// Turn off interrupts temporarily because the next sections // Turn off interrupts temporarily because the next sections
// are timing critical and we don't want any interruptions. // are timing critical and we don't want any interruptions.

3
DHT.h
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@ -39,7 +39,7 @@ written by Adafruit Industries
class DHT { class DHT {
public: public:
DHT(uint8_t pin, uint8_t type, uint8_t count=6); DHT(uint8_t pin, uint8_t type, uint8_t count=6);
void begin(void); void begin(uint8_t usec=55);
float readTemperature(bool S=false, bool force=false); float readTemperature(bool S=false, bool force=false);
float convertCtoF(float); float convertCtoF(float);
float convertFtoC(float); float convertFtoC(float);
@ -58,6 +58,7 @@ class DHT {
#endif #endif
uint32_t _lastreadtime, _maxcycles; uint32_t _lastreadtime, _maxcycles;
bool _lastresult; bool _lastresult;
uint8_t pullTime; // Time (in usec) to pull up data line before reading
uint32_t expectPulse(bool level); uint32_t expectPulse(bool level);

2
library.properties
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@ -1,5 +1,5 @@
name=DHT sensor library name=DHT sensor library
version=1.3.2 version=1.3.3
author=Adafruit author=Adafruit
maintainer=Adafruit <info@adafruit.com> maintainer=Adafruit <info@adafruit.com>
sentence=Arduino library for DHT11, DHT22, etc Temp & Humidity Sensors sentence=Arduino library for DHT11, DHT22, etc Temp & Humidity Sensors