mirror of
https://github.com/RobTillaart/Arduino.git
synced 2024-10-03 18:09:02 -04:00
181 lines
8.4 KiB
Markdown
181 lines
8.4 KiB
Markdown
|
|
[](https://github.com/marketplace/actions/arduino_ci)
|
|
[](https://github.com/RobTillaart/DHTNew/blob/master/LICENSE)
|
|
[](https://github.com/RobTillaart/DHTNew/releases)
|
|
|
|
# DHTNew
|
|
|
|
Arduino library for DHT11 and DHT22 with automatic sensor type recognition.
|
|
|
|
|
|
## Description
|
|
|
|
DHTNEW is stable for both ARM and AVR.
|
|
It is based upon the well tested DHTlib code.
|
|
|
|
|
|
## History
|
|
|
|
DHTNEW has some new features compared to the DHTlib code.
|
|
|
|
1. The constructor has a pin number, so the one sensor - one object paradigm is chosen.
|
|
So you can now make a DHTNEW object bathroom(4), kitchen(3), etc.
|
|
2. The **read()** function now reads both DHT11 and DHT22 sensors and selects the right
|
|
math per sensor based upon the bit patterns.
|
|
3. An **offset** can be set for both temperature and humidity to have a first-order linear
|
|
calibration in the class itself. Of course, this introduces a possible risk of
|
|
under- or overflow.
|
|
For a more elaborated or non-linear offset, I refer to my multimap class.
|
|
4. **lastRead()** keeps track of the last time the sensor is read. If this is not too long ago
|
|
one can decide not to read the sensors but use the current values for temperature and humidity.
|
|
This saves up to 20+ milliseconds for a DHT11 or 5+ millis for a DHT22. Note that these sensors
|
|
should have 1-2 seconds between reads according to specification.
|
|
In the future, this functionality could be inside the library by setting a time threshold
|
|
(e.g. 1 second by default) to give more stable results.
|
|
5. Added **interrupt enable/disable flag** to prevent interrupts disturb timing of DHT protocol.
|
|
Be aware that this may affect other parts of your application.
|
|
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.
|
|
7. (0.1.7) added **waitForReading flag** (kudos to Mr-HaleYa) to let the sensor explicitly
|
|
wait until a new value can be read.
|
|
8. (0.2.0) Temperature and humidity are private now, use **getTemperature()** and **getHumidity()**
|
|
9. (0.2.1) Adjusted the bit timing threshold to work around issue #11
|
|
10. (0.2.2) added **ERROR_SENSOR_NOT_READY** and differentiated timeout errors.
|
|
11. (0.3.0)
|
|
removed interrupt flag, now the library always disables interrupts during
|
|
the clocking of the bits.
|
|
Added getReadDelay & setReadDelay to tune reading interval. Check the example code.
|
|
Adjusted the timing in the wake-up part of the protocol.
|
|
Added more comments to describe the protocol.
|
|
12. (0.3.1)
|
|
added **powerDown()** and **powerUp()** for low power applications. Note that after **powerUp()**
|
|
the user must wait for two seconds before doing a read(). Just like after a (re)boot.
|
|
Note: The lib does not (yet) control the power pin of the sensor.
|
|
Discussion see https://github.com/RobTillaart/DHTNew/issues/13
|
|
13. (0.3.2)
|
|
Added **setSuppressError()** and **getSuppressError()** so the library will not output -999
|
|
but the last known valid value for temperature and humidity.
|
|
This flag is useful to suppress 'negative spikes' in graphs or logs.
|
|
Default the error values are not suppressed to be backwards compatible.
|
|
Added **#ifndef** around **DHTLIB_INVALID_VALUE** so the default -999 can be overruled
|
|
compile time to set another error value e.g. -127 or -1 whatever suits the project.
|
|
14. (0.3.3)
|
|
Refactored the low level **readSensor()** as the **BIT SHIFT ERROR** issue #29 and issue #11 popped up again.
|
|
It was reproduced "efficiently" with an ESP32 and by using long wires.
|
|
Fixed with an explicit digitalWrite(datapin, HIGH) + delayMicroseconds() to have enough time between
|
|
pulling the line HIGH and polling for the line LOW.
|
|
15. (0.3.4)
|
|
Added **waitFor(state, timeout)** to more precisely follow the datasheet in terms of timing.
|
|
Reintroduced the **interrupt enable/disable flag** as forced noInterrupts()
|
|
could break the timing of the DHT protocol / micros() - seen on AVR.
|
|
16. (0.4.0)
|
|
Added **DHTLIB_WAITING_FOR_READ** as return value of read => minor break of interface
|
|
17. (0.4.1)
|
|
Added Arduino-CI support + **gettype()** now tries to determine type if not known.
|
|
18. (0.4.2)
|
|
Fix negative temperatures. Tested with DHTNew_debug.ino and hexdump in .cpp and a freezer.
|
|
Note: testing in a freezer is not so good for humidity readings.
|
|
19. (0.4.3)
|
|
Added **reset()** to reset internal variables when a sensor blocks this might help.
|
|
Added **lastRead()** to return time the sensor is last read. (in millis).
|
|
20. (0.4.4)
|
|
DO NOT USE incorrect negative temp.
|
|
21. (0.4.5)
|
|
Prevent -0.0 when negative temp is 0;
|
|
DO NOT USE as it maps every negative temp to zero.
|
|
22. (0.4.6)
|
|
Fixed negative temperature (again).
|
|
|
|
|
|
|
|
## DHT PIN layout from left to right
|
|
|
|
| FRONT | | DESCRIPTION |
|
|
|:----|:----:|:----|
|
|
| pin 1 | | VCC |
|
|
| pin 2 | | DATA |
|
|
| pin 3 | | Not Connected |
|
|
| pin 4 | | GND |
|
|
|
|
|
|
## Specification DHT22
|
|
|
|
| Model | DHT22 | Notes |
|
|
|:----|:----|:----|
|
|
| Power supply | 3.3 - 6 V DC |
|
|
| Output signal | digital signal via single-bus |
|
|
| Sensing element | Polymer capacitor |
|
|
| Operating range | humidity 0-100% RH | temperature -40° - 80° Celsius |
|
|
| Accuracy humidity | ±2% RH(Max ±5% RH) | temperature < ±0.5° Celsius |
|
|
| Resolution or sensitivity | humidity 0.1% RH | temperature 0.1° Celsius |
|
|
| Repeatability humidity | ±1% RH | temperature ±0.2° Celsius |
|
|
| Humidity hysteresis | ±0.3% RH |
|
|
| Long-term Stability | ±0.5% RH/year |
|
|
| Sensing period | Average: 2s |
|
|
| Interchangeability | fully interchangeable |
|
|
| Dimensions | small 14 x 18 x 5.5 mm | big 22 x 28 x 5 mm |
|
|
|
|
|
|
## Interface
|
|
|
|
|
|
### Constructor
|
|
|
|
- **DHTNEW(uint8_t pin)** defines the datapin of the sensor.
|
|
- **reset()** might help to reset a sensor behaving badly. It does reset the library settings to default,
|
|
however it does not reset the sensor in a hardware way.
|
|
- **getType()** 0 = unknown, 11 or 22.
|
|
In case of 0, **getType()** will try to determine type.
|
|
- **setType(uint8_t type = 0)** allows to force the type of the sensor.
|
|
|
|
|
|
### Base interface
|
|
|
|
- **read()** reads a new temperature and humidity from the sensor
|
|
- **lastRead()** returns milliseconds since last **read()**
|
|
- **getHumidity()** returns last read value (float) or -999 in case of error.
|
|
Note this error value can be suppressed by **setSuppressError(bool)**.
|
|
- **getTemperature()** returns last read value (float) or -999 in case of error. Note this error value can be suppressed by **setSuppressError(bool)**.
|
|
|
|
|
|
### Offset
|
|
|
|
Adding offsets works well in normal range however they might introduce under- or overflow at the ends of the sensor range.
|
|
|
|
- **setHumOffset(float offset)** typical < ±5% RH.
|
|
- **setTempOffset(float offset)** typical < ±2°C.
|
|
- **getHumOffset()** idem.
|
|
- **getTempOffset()** idem.
|
|
|
|
|
|
### Control
|
|
|
|
Functions to adjust the communication with the sensor.
|
|
|
|
- **setDisableIRQ(bool b )** allows or suppresses interrupts during core read function to keep timing as correct as possible. **Note AVR only**
|
|
- **getDisableIRQ()** returns the above setting. Default **false**
|
|
- **setWaitForReading(bool b )** flag to enforce a blocking wait.
|
|
- **getWaitForReading()** returns the above setting.
|
|
- **setReadDelay(uint16_t rd = 0)** To tune the time it waits before actual read. This reduces the blocking time. Default depends on type. 1000 ms (dht11) or 2000 ms (dht22). set readDelay to 0 will reset to datasheet values AFTER a call to **read()**.
|
|
- **getReadDelay()** returns the above setting.
|
|
- **powerDown()** pulls datapin down to reduce power consumption
|
|
- **powerUp()** restarts the sensor, note one must wait up to two seconds.
|
|
- **setSuppressError(bool b)** suppress error values of -999 => you need to check the return value of read() instead.
|
|
This is used to keep spikes out of your graphs / logs.
|
|
- **getSuppressError()** returns the above setting.
|
|
|
|
|
|
## Operation
|
|
|
|
See examples
|
|
|
|
If consistent problems occur with reading a sensor, one should allow interrupts
|
|
**DHT.setDisableIRQ(true)**
|
|
|
|
|
|
## ESP8266 & DHT22
|
|
|
|
- The DHT22 sensor has some problems in combination with specific pins of the ESP8266. See more details
|
|
- https://github.com/RobTillaart/DHTNew/issues/31 (message Jan 3, 2021)
|
|
- https://github.com/arendst/Tasmota/issues/3522
|
|
|