Ko de Beer
Member
Hey, I'm trying to use a dht11 temperature and humidity sensor with my Teensy 3.6.
But I when I try to get a reading on the serial monitor it says "Failed to read from DHT sensor!".
When I did all of this on Arduino it worked fine. Maybe it has something to do with the clock speed of the teensy?
Or am I maybe connecting it up in the wrong way?
I connect the sensor like this:
Dht 3 pin version:
I connect the sensor pin to digital pin2 of the Teensy.
The ground of the sensor to GND of the teensy.
The vcc of the dht11 to the Vin of the teensy.
The code I use:
The Adafruit DHT.cpp
Maybe I should change some delays in the adafruit DHT.cpp to match the clockspeed?
To what speed should I set it?
Thank you for reading and thanks for the help!
But I when I try to get a reading on the serial monitor it says "Failed to read from DHT sensor!".
When I did all of this on Arduino it worked fine. Maybe it has something to do with the clock speed of the teensy?
Or am I maybe connecting it up in the wrong way?
I connect the sensor like this:
Dht 3 pin version:
I connect the sensor pin to digital pin2 of the Teensy.
The ground of the sensor to GND of the teensy.
The vcc of the dht11 to the Vin of the teensy.
The code I use:
Code:
// Example testing sketch for various DHT humidity/temperature sensors
// Written by ladyada, public domain
// REQUIRES the following Arduino libraries:
// - DHT Sensor Library: [url]https://github.com/adafruit/DHT-sensor-library[/url]
// - Adafruit Unified Sensor Lib: [url]https://github.com/adafruit/Adafruit_Sensor[/url]
#include "DHT.h"
#define DHTPIN 1 // Digital pin connected to the DHT sensor
// Feather HUZZAH ESP8266 note: use pins 3, 4, 5, 12, 13 or 14 --
// Pin 15 can work but DHT must be disconnected during program upload.
// Uncomment whatever type you're using!
#define DHTTYPE DHT11 // DHT 11
//#define DHTTYPE DHT22 // DHT 22 (AM2302), AM2321
//#define DHTTYPE DHT21 // DHT 21 (AM2301)
// Connect pin 1 (on the left) of the sensor to +5V
// NOTE: If using a board with 3.3V logic like an Arduino Due connect pin 1
// to 3.3V instead of 5V!
// Connect pin 2 of the sensor to whatever your DHTPIN is
// Connect pin 4 (on the right) of the sensor to GROUND
// Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor
// Initialize DHT sensor.
// Note that older versions of this library took an optional third parameter to
// tweak the timings for faster processors. This parameter is no longer needed
// as the current DHT reading algorithm adjusts itself to work on faster procs.
DHT dht(DHTPIN, DHTTYPE);
void setup() {
Serial.begin(9600);
Serial.println(F("DHTxx test!"));
dht.begin();
}
void loop() {
// Wait a few seconds between measurements.
delay(2000);
// Reading temperature or humidity takes about 250 milliseconds!
// Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
float h = dht.readHumidity();
// Read temperature as Celsius (the default)
float t = dht.readTemperature();
// Read temperature as Fahrenheit (isFahrenheit = true)
float f = dht.readTemperature(true);
// Check if any reads failed and exit early (to try again).
if (isnan(h) || isnan(t) || isnan(f)) {
Serial.println(F("Failed to read from DHT sensor!"));
return;
}
// Compute heat index in Fahrenheit (the default)
float hif = dht.computeHeatIndex(f, h);
// Compute heat index in Celsius (isFahreheit = false)
float hic = dht.computeHeatIndex(t, h, false);
Serial.print(F("Humidity: "));
Serial.print(h);
Serial.print(F("% Temperature: "));
Serial.print(t);
Serial.print(F("°C "));
Serial.print(f);
Serial.print(F("°F Heat index: "));
Serial.print(hic);
Serial.print(F("°C "));
Serial.print(hif);
Serial.println(F("°F"));
}The Adafruit DHT.cpp
Maybe I should change some delays in the adafruit DHT.cpp to match the clockspeed?
To what speed should I set it?
Code:
/* DHT library
MIT license
written by Adafruit Industries
*/
#include "DHT.h"
#define MIN_INTERVAL 2000
#define TIMEOUT -1
DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
_pin = pin;
_type = type;
#ifdef __AVR
_bit = digitalPinToBitMask(pin);
_port = digitalPinToPort(pin);
#endif
_maxcycles = microsecondsToClockCycles(1000); // 1 millisecond timeout for
// reading pulses from DHT sensor.
// Note that count is now ignored as the DHT reading algorithm adjusts itself
// based on the speed of the processor.
}
// 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!
pinMode(_pin, INPUT_PULLUP);
// Using this value makes sure that millis() - lastreadtime will be
// >= MIN_INTERVAL right away. Note that this assignment wraps around,
// but so will the subtraction.
_lastreadtime = millis() - MIN_INTERVAL;
DEBUG_PRINT("DHT max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC);
pullTime = usec;
}
//boolean S == Scale. True == Fahrenheit; False == Celcius
float DHT::readTemperature(bool S, bool force) {
float f = NAN;
if (read(force)) {
switch (_type) {
case DHT11:
f = data[2];
if (data[3] & 0x80) {
f = -1 - f ;
}
f += (data[3] & 0x0f) * 0.1;
if(S) {
f = convertCtoF(f);
}
break;
case DHT12:
f = data[2];
f += (data[3] & 0x0f) * 0.1;
if (data[2] & 0x80) {
f *= -1;
}
if(S) {
f = convertCtoF(f);
}
break;
case DHT22:
case DHT21:
f = ((word)(data[2] & 0x7F)) << 8 | data[3];
f *= 0.1;
if (data[2] & 0x80) {
f *= -1;
}
if(S) {
f = convertCtoF(f);
}
break;
}
}
return f;
}
float DHT::convertCtoF(float c) {
return c * 1.8 + 32;
}
float DHT::convertFtoC(float f) {
return (f - 32) * 0.55555;
}
float DHT::readHumidity(bool force) {
float f = NAN;
if (read(force)) {
switch (_type) {
case DHT11:
case DHT12:
f = data[0] + data[1] * 0.1;
break;
case DHT22:
case DHT21:
f = ((word)data[0]) << 8 | data[1];
f *= 0.1;
break;
}
}
return f;
}
//boolean isFahrenheit: True == Fahrenheit; False == Celcius
float DHT::computeHeatIndex(bool isFahrenheit) {
float hi = computeHeatIndex(readTemperature(isFahrenheit), readHumidity(),
isFahrenheit);
return isFahrenheit ? hi : convertFtoC(hi);
}
//boolean isFahrenheit: True == Fahrenheit; False == Celcius
float DHT::computeHeatIndex(float temperature, float percentHumidity,
bool isFahrenheit) {
// Using both Rothfusz and Steadman's equations
// http://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml
float hi;
if (!isFahrenheit)
temperature = convertCtoF(temperature);
hi = 0.5 * (temperature + 61.0 + ((temperature - 68.0) * 1.2) + (percentHumidity * 0.094));
if (hi > 79) {
hi = -42.379 +
2.04901523 * temperature +
10.14333127 * percentHumidity +
-0.22475541 * temperature*percentHumidity +
-0.00683783 * pow(temperature, 2) +
-0.05481717 * pow(percentHumidity, 2) +
0.00122874 * pow(temperature, 2) * percentHumidity +
0.00085282 * temperature*pow(percentHumidity, 2) +
-0.00000199 * pow(temperature, 2) * pow(percentHumidity, 2);
if((percentHumidity < 13) && (temperature >= 80.0) && (temperature <= 112.0))
hi -= ((13.0 - percentHumidity) * 0.25) * sqrt((17.0 - abs(temperature - 95.0)) * 0.05882);
else if((percentHumidity > 85.0) && (temperature >= 80.0) && (temperature <= 87.0))
hi += ((percentHumidity - 85.0) * 0.1) * ((87.0 - temperature) * 0.2);
}
return isFahrenheit ? hi : convertFtoC(hi);
}
bool DHT::read(bool force) {
// Check if sensor was read less than two seconds ago and return early
// to use last reading.
uint32_t currenttime = millis();
if (!force && ((currenttime - _lastreadtime) < MIN_INTERVAL)) {
return _lastresult; // return last correct measurement
}
_lastreadtime = currenttime;
// Reset 40 bits of received data to zero.
data[0] = data[1] = data[2] = data[3] = data[4] = 0;
#if defined(ESP8266)
yield(); // Handle WiFi / reset software watchdog
#endif
// Send start signal. See DHT datasheet for full signal diagram:
// http://www.adafruit.com/datasheets/Digital%20humidity%20and%20temperature%20sensor%20AM2302.pdf
// Go into high impedence state to let pull-up raise data line level and
// start the reading process.
pinMode(_pin, INPUT_PULLUP);
delay(1);
// First set data line low for a period according to sensor type
pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
switch(_type) {
case DHT22:
case DHT21:
delayMicroseconds(1100); // data sheet says "at least 1ms"
break;
case DHT11:
default:
delay(20); //data sheet says at least 18ms, 20ms just to be safe
break;
}
uint32_t cycles[80];
{
// End the start signal by setting data line high for 40 microseconds.
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.
// Turn off interrupts temporarily because the next sections
// are timing critical and we don't want any interruptions.
InterruptLock lock;
// First expect a low signal for ~80 microseconds followed by a high signal
// for ~80 microseconds again.
if (expectPulse(LOW) == TIMEOUT) {
DEBUG_PRINTLN(F("DHT timeout waiting for start signal low pulse."));
_lastresult = false;
return _lastresult;
}
if (expectPulse(HIGH) == TIMEOUT) {
DEBUG_PRINTLN(F("DHT timeout waiting for start signal high pulse."));
_lastresult = false;
return _lastresult;
}
// Now read the 40 bits sent by the sensor. Each bit is sent as a 50
// microsecond low pulse followed by a variable length high pulse. If the
// high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds
// then it's a 1. We measure the cycle count of the initial 50us low pulse
// and use that to compare to the cycle count of the high pulse to determine
// if the bit is a 0 (high state cycle count < low state cycle count), or a
// 1 (high state cycle count > low state cycle count). Note that for speed all
// the pulses are read into a array and then examined in a later step.
for (int i=0; i<80; i+=2) {
cycles[i] = expectPulse(LOW);
cycles[i+1] = expectPulse(HIGH);
}
} // Timing critical code is now complete.
// Inspect pulses and determine which ones are 0 (high state cycle count < low
// state cycle count), or 1 (high state cycle count > low state cycle count).
for (int i=0; i<40; ++i) {
uint32_t lowCycles = cycles[2*i];
uint32_t highCycles = cycles[2*i+1];
if ((lowCycles == TIMEOUT) || (highCycles == TIMEOUT)) {
DEBUG_PRINTLN(F("DHT timeout waiting for pulse."));
_lastresult = false;
return _lastresult;
}
data[i/8] <<= 1;
// Now compare the low and high cycle times to see if the bit is a 0 or 1.
if (highCycles > lowCycles) {
// High cycles are greater than 50us low cycle count, must be a 1.
data[i/8] |= 1;
}
// Else high cycles are less than (or equal to, a weird case) the 50us low
// cycle count so this must be a zero. Nothing needs to be changed in the
// stored data.
}
DEBUG_PRINTLN(F("Received from DHT:"));
DEBUG_PRINT(data[0], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[1], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[2], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[3], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[4], HEX); DEBUG_PRINT(F(" =? "));
DEBUG_PRINTLN((data[0] + data[1] + data[2] + data[3]) & 0xFF, HEX);
// Check we read 40 bits and that the checksum matches.
if (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
_lastresult = true;
return _lastresult;
}
else {
DEBUG_PRINTLN(F("DHT checksum failure!"));
_lastresult = false;
return _lastresult;
}
}
// Expect the signal line to be at the specified level for a period of time and
// return a count of loop cycles spent at that level (this cycle count can be
// used to compare the relative time of two pulses). If more than a millisecond
// ellapses without the level changing then the call fails with a 0 response.
// This is adapted from Arduino's pulseInLong function (which is only available
// in the very latest IDE versions):
// https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/wiring_pulse.c
uint32_t DHT::expectPulse(bool level) {
#if (F_CPU > 16000000L)
uint32_t count = 0;
#else
uint16_t count = 0; // To work fast enough on slower AVR boards
#endif
// On AVR platforms use direct GPIO port access as it's much faster and better
// for catching pulses that are 10's of microseconds in length:
#ifdef __AVR
uint8_t portState = level ? _bit : 0;
while ((*portInputRegister(_port) & _bit) == portState) {
if (count++ >= _maxcycles) {
return TIMEOUT; // Exceeded timeout, fail.
}
}
// Otherwise fall back to using digitalRead (this seems to be necessary on ESP8266
// right now, perhaps bugs in direct port access functions?).
#else
while (digitalRead(_pin) == level) {
if (count++ >= _maxcycles) {
return TIMEOUT; // Exceeded timeout, fail.
}
}
#endif
return count;
}Thank you for reading and thanks for the help!
