DHT 11 Humidity & Temperature
Sensor

1.Introduction

The DHT11 Temperature & Humidity Sensor features a temperature & humidity sensor
complex with a calibrated digital signal output. By using the exclusive digital-signal-acquisition
technique and temperature & humidity sensing technology, it ensures high reliability andexcellent long-term stability. This sensor includes a resistive-type humidity measurement
component and an NTC temperature measurement component, and connects to a highperformance 8-bit microcontroller, offering excellent quality, fast response, anti-interferenceabilityand cost-effectiveness.

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Each DHT11 sensor is strictly calibrated in the laboratory that is extremely accurate on
humidity calibration. The calibration coefficients are stored as programmes in the OTP memory,which are used by the sensor’s internal signal detecting process. The single-wire serial interface
makes system integration quick and easy. Its small size, low power consumption and up-to-20
meter signal transmission making it the best choice for various applications, including thosemost demanding ones. The component is 4-pin single row pin package. It is convenient toconnect and special packagescan be provided accordingto users’ request.

2.Technical Specifications:
Overview:
Item
DHT11Page | 2

Measurement Humidity
Range
Accuracy
20-90%RH± 5 RH
0-50℃

Temperature
Accuracy± 2℃

Resolution

Package

14Pin Single
RowDetailedSpecifications:Parameters
Humidity
Resolution
Repeatability
Accuracy

Conditions

Minimum

TypicalMaximum

1%RH

1%RH
8Bit
± 1%RH± 4%RH

1%RH

25℃
0-50℃
Interchangeability FullyInterchangeable
Measurement
30%RH
0℃
Range
20%RH
25℃
20%RH
50℃
ResponseTime
6S1/e(63%)25℃(Seconds)
1m/sAir
Hysteresis
Long-Term
TypicalStability
Temperature
Resolution
1℃
8Bit
Repeatability
Accuracy± 1℃
Measurement
0℃
Range
ResponseTime
1/e(63%)
6S(Seconds)

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10S± 5%RH
90%RH
90%RH
80%RH
15S

± 1%RH± 1%RH/year
1℃
8Bit
± 1℃

1℃
8Bit
± 2℃
50℃
30S

3.Typical Application (Figure1)

Figure1Typical Application
Note: 3Pin – Null; MCU =Micro-computer Unite or single chip Computer
When the connectingcable isshorter than 20 metres, a5Kpull-up resistor isrecommended;
when the connectingcable islonger than 20metres, choose aappropriate pull-up resistor asneeded.

4.Power and Pin

DHT11’spower supplyis3-5.5VDC. When power issupplied to the sensor, do not send any
instruction to the sensor in within one second in order to passthe unstable status. One
capacitor valued 100nF can be added between VDDand GNDfor power filtering.

5.Communication Process:Serial Interface(Single-WireTwo-Way)

Single-bus data format is used for communication and synchronization between MCU andDHT11sensor. One communication processisabout 4ms.
Data consists of decimal and integral parts. A complete data transmission is 40bit, and thesensor sendshigherdatabitfirst.
Dataformat: 8bit integral RH data +8bit decimal RH data +8bit integral T data +8bit decimal T
data +8bit check sum. If the data transmission is right, the check-sumshould be the last 8bit of"8bit integral RHdata+8bit decimal RH data+8bit integral Tdata+8bit decimal Tdata".

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5.1 Overall Communication Process(Figure2,below)

When MCU sends a start signal, DHT11 changes from the low-power-consumption mode to therunning-mode, waitingfor MCU completingthe start signal. Once it iscompleted, DHT11 sendsa
response signal of 40-bit data that include the relative humidity and temperature information toMCU. Users can choose to collect (read) some data. Without the start signal fromMCU, DHT11
will not give the response signal to MCU. Once data is collected, DHT11 will change to the lowpower-consumption mode until it receivesastart signal fromMCU again.

Figure2Overall CommunicationProcess

5.2 MCUSendsout StartSignal to DHT (Figure3,below)

Data Single-bus free status is at high voltage level. When the communication between MCU andDHT11 begins, the programme of MCU will set Data Single-bus voltage level from high to low
and this process must take at least 18ms to ensure DHT’s detection of MCU's signal, then MCU
will pull up voltage and wait 20-40usfor DHT’sresponse.

Figure3MCUSendsoutStartSignal &DHTResponses

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5.3 DHT ResponsestoMCU (Figure3,above)

Once DHTdetects the start signal, it will send out alow-voltage-level response signal, whichlasts80us. Then the programme of DHTsetsDataSingle-busvoltage level fromlow to high andkeepsit for 80usfor DHT’s preparation for sendingdata.
When DATA Single-Busisat the low voltage level, thismeansthat DHTissendingthe responsesignal. Once DHTsent out the response signal, it pullsup voltage and keepsit for 80us andpreparesfor datatransmission.
When DHTissendingdatato MCU, everybit of databeginswith the 50uslow-voltage-level andthe length of the followinghigh-voltage-level signal determineswhether databit is"0" or "1"(see Figures4and 5below).

Figure4Data"0" Indication

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Figure5Data"1" Indication

If the response signal fromDHTisalwaysat high-voltage-level, it suggeststhat DHTisnot
respondingproperlyand please checkthe connection. When the last bit data istransmitted,
DHT11pullsdown the voltage level and keepsit for 50us. Then the Single-Busvoltage will bepulled up bythe resistor to set it backto the free status.

6.Electrical Characteristics

VDD=5V, T=25℃(unlessotherwise stated)
Conditions
Minimum
Power Supply DC
3V
Current
Measuring
0.5mA
SupplyAverage
0.2mAStandby
100uA
Sampling
Second1
periodTypical5V

Maximum
5.5V
2.5mA
1mA
150uA

Note: Samplingperiod at intervals should be no lessthan 1second.

7. Attentionsof application(1) Operatingconditions
Applyingthe DHT11sensor beyond its workingrange stated inthisdatasheet can result in 3%RH
signal shift/discrepancy. The DHT11sensor can recover to the calibrated status graduallywhen
it getsbackto the normal operatingcondition and workswithin itsrange. Please refer to (3) ofPage | 7thissection to accelerate itsrecovery. Please be awarethat operatingthe DHT11 sensor in thenon-normal workingconditionswill accelerate sensor’sagingprocess.
(2) Attention tochemical materials
Vapor fromchemical materialsmayinterfere with DHT’ssensitive-elementsand debase itssensitivity. A high degree of chemical contamination can permanentlydamage the sensor.
(3) Restoration processwhen (1) &(2) happen
Step one: Keep the DHTsensor at the condition of Temperature50~60Celsius, humidity<10%RH
for 2hours;
Step two:Kkeep the DHTsensor at the condition of Temperature 20~30Celsius, humidity>70%RHfor 5hours.
(4) TemperatureAffect
Relative humiditylargelydependson temperature. Although temperature compensation
technologyisused to ensure accurate measurement of RH, it isstill stronglyadvised to keep thehumidityand temperature sensorsworkingunder the same temperature. DHT11should be
mounted at the place asfar as possible frompartsthat may generate heat.
(5) Light AffectLongtime exposure to strongsunlight and ultraviolet maydebase DHT’sperformance.
(6) Connection wires
The qualityof connection wireswill affect the qualityand distance of communication and highqualityshielding-wire isrecommended.
(7) Other attentions* Weldingtemperature should be bellow 260Celsiusand contact should take lessthan 10seconds.
* Avoid usingthe sensor under dew condition.
* Do not use thisproduct in safetyor emergencystop devicesor anyother occasion that failureof DHT11maycause personal injury.
* Storage: Keep the sensor at temperature10-40℃, humidity<60%RH.

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