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234 lines
11 KiB
Markdown
234 lines
11 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/DHTNew/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/DHTNew/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/DHTNew/blob/master/LICENSE)
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[](https://github.com/RobTillaart/DHTNew/releases)
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# DHTNew
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Arduino library for DHT11 and DHT22 (and compatible) with automatic sensor type recognition.
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## Description
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DHTNEW is stable for both ARM and AVR. It is based upon the well tested DHTlib code.
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This is the main development library of all my DHT libraries.
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Supports DHT11, DHT22, DHT33, DHT44, AM2301, AM2302, AM2303 as these all have the same protocol.
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Note there are differences e.g. DHT11 has no negative temperature, no decimals, and a longer wakeup time.
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## DHT PIN layout from left to right
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| Front | | Description |
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|:------|:----:|:--------------|
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| pin 1 | | VCC |
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| pin 2 | | DATA |
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| pin 3 | | Not Connected |
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| pin 4 | | GND |
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## Specification DHT22
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| Model | DHT22 | Notes |
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|:--------------------------|:-----------------------|:------|
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| Power supply | 3.3 - 6 V DC |
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| Output signal | digital signal via single-bus |
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| Sensing element | Polymer capacitor |
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| Operating range | humidity 0-100% RH | temperature -40° - 80° Celsius
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| Accuracy humidity | ±2% RH(Max ±5% RH) | temperature < ±0.5° Celsius
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| Resolution or sensitivity | humidity 0.1% RH | temperature 0.1° Celsius
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| Repeatability humidity | ±1% RH | temperature ±0.2° Celsius
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| Humidity hysteresis | ±0.3% RH |
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| Long-term Stability | ±0.5% RH/year |
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| Sensing period | Average: 2s |
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| Interchangeability | fully interchangeable |
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| Dimensions | small 14 x 18 x 5.5 mm | big 22 x 28 x 5 mm |
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## Interface
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### Constructor
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- **DHTNEW(uint8_t pin)** defines the dataPin of the sensor.
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- **void reset()** might help to reset a sensor behaving badly. It does reset the library settings to default,
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however it does not reset the sensor in a hardware way.
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- **uint8_t getType()** 0 = unknown, 11 or 22.
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In case of 0, **getType()** will try to determine type.
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- **void setType(uint8_t type = 0)** allows to force the type of the sensor.
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### Base interface
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- **int read()** reads a new temperature and humidity from the sensor
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- **uint32_t lastRead()** returns milliseconds since last **read()**
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- **float getHumidity()** returns last read value (float) or -999 in case of error.
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Note this error value can be suppressed by **setSuppressError(bool)**.
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- **float getTemperature()** returns last read value (float) or -999 in case of error. Note this error value can be suppressed by **setSuppressError(bool)**.
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### Offset
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Adding offsets works well in normal range however they might introduce under- or overflow at the ends of the sensor range.
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humidity is constrained to 0..100% in the code. For temperature such constrain would be type dependant, so not done.
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- **void setHumOffset(float offset)** typical < ±5% RH.
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- **void setTempOffset(float offset)** typical < ±2°C.
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- **float getHumOffset()** idem.
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- **float getTempOffset()** idem.
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### Control
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Functions to adjust the communication with the sensor.
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- **void setDisableIRQ(bool b )** allows or suppresses interrupts during core read function to keep timing as correct as possible. **Note AVR + MKR1010**
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- **bool getDisableIRQ()** returns the above setting. Default **true**.
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- **void setWaitForReading(bool b )** flag to enforce a blocking wait.
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- **bool getWaitForReading()** returns the above setting.
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- **void setReadDelay(uint16_t rd = 0)** To tune the time it waits before actual read. This reduces the blocking time.
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Default depends on type. 1000 ms (dht11) or 2000 ms (dht22).
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set readDelay to 0 will reset to datasheet values AFTER a call to **read()**.
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- **uint16_t getReadDelay()** returns the above setting.
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- **void powerDown()** pulls dataPin down to reduce power consumption
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- **void powerUp()** restarts the sensor, note one must wait up to two seconds.
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- **void setSuppressError(bool b)** suppress error values of -999 => you need to check the return value of read() instead.
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This is used to keep spikes out of your graphs / logs.
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- **bool getSuppressError()** returns the above setting.
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## Operation
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See examples
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#### TIME_OUT
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If consistent TIMOUT_C or TIMEOUT_D occur during reading a sensor,
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one could try if allowing interrupts solves the issue **DHT.setDisableIRQ(false)**.
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This solved this problem at least on
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- AVR boards - is build into the constructor
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- MKR1010 Wifi - see https://github.com/RobTillaart/DHTNew/issues/67
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(added as comment in the examples)
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In version 0.4.10 the TIMEOUT_C is extended from 70-90 us to even suppress the TIMEOUT_C
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even more. See discussion and tests in https://github.com/RobTillaart/DHTNew/issues/67.
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#### Serial
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The MKR1010Wifi board need to wait for Serial at startup if you want to monitor it
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from the IDE. Adding the line ```while(!Serial):``` fixes this. (added to the examples).
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There might be more boards that need this line to work properly.
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#### ESP8266 & DHT22
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- The DHT22 sensor has some problems in combination with specific pins of the ESP8266. See more details
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- https://github.com/RobTillaart/DHTNew/issues/31 (message Jan 3, 2021)
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- https://github.com/arendst/Tasmota/issues/3522
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## History
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DHTNEW has some new features compared to the DHTlib code.
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1. The constructor has a pin number, so the one sensor - one object paradigm is chosen.
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So you can now make a DHTNEW object bathroom(4), kitchen(3), etc.
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2. The **read()** function now reads both DHT11 and DHT22 sensors and selects the right
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math per sensor based upon the bit patterns.
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3. An **offset** can be set for both temperature and humidity to have a first-order linear
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calibration in the class itself. Of course, this introduces a possible risk of
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under- or overflow.
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For a more elaborated or non-linear offset, I refer to my multimap class.
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4. **lastRead()** keeps track of the last time the sensor is read. If this is not too long ago
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one can decide not to read the sensors but use the current values for temperature and humidity.
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This saves up to 20+ milliseconds for a DHT11 or 5+ milliseconds for a DHT22. Note that these sensors
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should have 1-2 seconds between reads according to specification.
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In the future, this functionality could be inside the library by setting a time threshold
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(e.g. 1 second by default) to give more stable results.
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5. Added **interrupt enable/disable flag** to prevent interrupts disturb timing of DHT protocol.
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Be aware that this may affect other parts of your application.
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6. (0.1.7) added an automatic check of lastRead in the read call. If request a read to fast it will just return OK.
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7. (0.1.7) added **waitForReading flag** (kudos to Mr-HaleYa) to let the sensor explicitly
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wait until a new value can be read.
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8. (0.2.0) Temperature and humidity are private now, use **getTemperature()** and **getHumidity()**
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9. (0.2.1) Adjusted the bit timing threshold to work around issue #11
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10. (0.2.2) added **ERROR_SENSOR_NOT_READY** and differentiated timeout errors.
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11. (0.3.0)
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removed interrupt flag, now the library always disables interrupts during
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the clocking of the bits.
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Added getReadDelay & setReadDelay to tune reading interval. Check the example code.
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Adjusted the timing in the wake-up part of the protocol.
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Added more comments to describe the protocol.
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12. (0.3.1)
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added **powerDown()** and **powerUp()** for low power applications. Note that after **powerUp()**
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the user must wait for two seconds before doing a read(). Just like after a (re)boot.
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Note: The lib does not (yet) control the power pin of the sensor.
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Discussion see https://github.com/RobTillaart/DHTNew/issues/13
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13. (0.3.2)
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Added **setSuppressError()** and **getSuppressError()** so the library will not output -999
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but the last known valid value for temperature and humidity.
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This flag is useful to suppress 'negative spikes' in graphs or logs.
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Default the error values are not suppressed to be backwards compatible.
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Added **#ifndef** around **DHTLIB_INVALID_VALUE** so the default -999 can be overruled
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compile time to set another error value e.g. -127 or -1 whatever suits the project.
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14. (0.3.3)
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Refactored the low level **readSensor()** as the **BIT SHIFT ERROR** issue #29 and issue #11 popped up again.
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It was reproduced "efficiently" with an ESP32 and by using long wires.
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Fixed with an explicit digitalWrite(dataPin, HIGH) + delayMicroseconds() to have enough time between
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pulling the line HIGH and polling for the line LOW.
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15. (0.3.4)
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Added **waitFor(state, timeout)** to more precisely follow the datasheet in terms of timing.
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Reintroduced the **interrupt enable/disable flag** as forced noInterrupts()
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could break the timing of the DHT protocol / micros() - seen on AVR.
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16. (0.4.0)
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Added **DHTLIB_WAITING_FOR_READ** as return value of read => minor break of interface
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17. (0.4.1)
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Added Arduino-CI support + **gettype()** now tries to determine type if not known.
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18. (0.4.2)
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Fix negative temperatures. Tested with DHTNew_debug.ino and hex dump in .cpp and a freezer.
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Note: testing in a freezer is not so good for humidity readings.
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19. (0.4.3)
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Added **reset()** to reset internal variables when a sensor blocks this might help.
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Added **lastRead()** to return time the sensor is last read. (in milliseconds).
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20. (0.4.4)
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DO NOT USE incorrect negative temp.
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21. (0.4.5)
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Prevent -0.0 when negative temp is 0;
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DO NOT USE as it maps every negative temp to zero.
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22. (0.4.6)
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Fixed negative temperature (again).
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23. (0.4.7)
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fix #60 negative temperatures below -25.5°C + readme.md.
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24. (0.4.8)
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fixes to improve Arduino-lint.
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25. (0.4.9)
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add optional flag DHTLIB_VALUE_OUT_OF_RANGE.
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26. (0.4.10)
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updated build-CI to do compile test - UNO, due, zero, Leonardo, m4, esp32, esp8266, mega2560.
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updated readme.md - added badges and remarks after testing with MKR1010 Wifi.
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updated TIMEOUT_C from 70 -> 90 us to minimize its occurrence - See https://github.com/RobTillaart/DHTNew/issues/67.
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added ```while(!Serial);``` in examples to they work for MKR1010 Wifi.
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27. (0.4.11)
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update library.json, license, minor edits (cleanup), unit tests
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## Future
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- test on more boards
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- investigate temperature constraining (type dependant.
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- update documentation
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- move history to separate release_notes.md file ?
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- improve unit test
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- fix DHTLIB_VALUE_OUT_OF_RANGE code
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- #if defined(MKR1010) // TODO find out real define
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-
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