Controlling 12V DC motor w/ sht11 temp. humidity sensor

Matt K · 2007-05-30 22:30

I need help turning a 12 V dc fan on once the sht11 reads a desired temperature and humidity.· I can light a LED but not at the desired range.· Can anyone help me with this?

Franklin · 2007-05-31 02:00

Show us what you have and maybe we can help. You would do this the same way you switch any load, with a relay, transistor or a mosfet.

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- Stephen

Matt K · 2007-05-31 12:58

I am using a transistor.· I took the code from the parallax web page and the sht11 works fine.· I plan on using an IF temp. < x THEN HIGH statement but Im not sure what to use for X.· I want the fan to come on at 75 deg. and 45% humidity.· Am I going about this wrong?· Also when I hook the dc motor to my homework board, I'll need a 12V power source.· Will this affect my board? It just has the one 9 v battery.

Chris Savage · 2007-05-31 14:14

Matt,

If you want to switch when both the temperature and humidity are past a set point then your conditional will have to be more like:

IF temp > SetTemp AND humidity > SetHumidity THEN

As for the 12V, you will need the power source for the motor and it will need a common ground with the H/W Board. The transistor or MOSFET will handle the switching of the load so it shouldn’t interfere with your board as long as the current is not unusually high. Take care.

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Chris Savage
Parallax Tech Support

Matt K · 2007-05-31 15:07

I want the fan to switch on when the temp either/or the humidity reaches a setpoint.· Ive been testing the setpoints with LEDs, but Im having problems.· I cant just enter a temp or humidity reading, such as tF <·80 or rhLin < 45.
If I had a LED hooked to pin 14, what should my code consist of to turn the LED on at say·80 degrees or higher?
This is the first time Ive ever used the basic stamp so Im a little confused.· Thanks for the help.
·

Chris Savage · 2007-05-31 15:18

Matt,

IF tF < 80 OR rhLin < 45 THEN
  HIGH 14
ELSE
  LOW 14
ENDIF

This is, of course, assuming that the variable tF provides an integer·temperature such as 80 and that rhLin provides the relative humidity in percent as a whole number as well.· If not these values would have to be conditioned before this point.· Take care.

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Chris Savage
Parallax Tech Support

Matt K · 2007-05-31 18:45

My If Then statement looks like the one you sent me but I wasnt sure where to insert it.· Once I placed it in the code that I have included the LEDs would come on when the temp or humidity was below the setpoint rather than above it.· I must be placing it in the wrong location.· I place it after· "tF....... ", DEC (tF / 10), ".", DEC1 tF, DegSym, " "· and after "rhTrue... ", DEC (rhTrue / 10), ".", DEC1 rhTrue, "% ".· Is this wrong?
[font=Arial,Bold]BASIC Stamp Application
[/font]The following BASIC Stamp application will read the SHT11 sensor module and display sensor counts,
converted temperature and calibrated humidity. When running, the program output will appear as
shown below:
' =========================================================================
'
' File...... SHT11_Demo.BS2
' Purpose... Interface to Sensirion SHT11 temperature/humidity sensor
' Author.... Parallax
' E-mail.... support@parallax.com
' Started...
' Updated... 19 JUL 2003
'
' {$STAMP BS2}
' {$PBASIC 2.5}
'
' =========================================================================
'

' Program Description
'

'
Parallax, Inc. • Sensirion SHT11 Sensor Module (#28018) • 07/2003 3
' This program demonstrates the interface and conversion of SHT11/15 data
' to usable program values. This program uses advanced math features of
' PBASIC, specifically the ** operator.
'
' For detailed application information on the use and application of the
' ** operator, see Dr. Tracy Allen's web page at this link:
'
' -- http://www.emesystems.com/BS2math1.htm
'
' For SHT11/15 documentation and app notes, visit:
'
' -- http://www.sensirion.com
'

' Revision History
'

'

' I/O Definitions
'

ShtData PIN 1 ' bi-directional data
Clock PIN 0
'

' Constants
'

ShtTemp CON %00011 ' read temperature
ShtHumi CON %00101 ' read humidity
ShtStatW CON %00110 ' status register write
ShtStatR CON %00111 ' status register read
ShtReset CON %11110 ' soft reset
Ack CON 0
NoAck CON 1
No CON 0
Yes CON 1
DegSym CON 186 ' degrees symbol for DEBUG
'

' Variables
'

Parallax, Inc. • Sensirion SHT11 Sensor Module (#28018) • 07/2003 4
ioByte VAR Byte ' data from/to SHT11
ackBit VAR Bit ' ack/nak from/to SHT11
toDelay VAR Byte ' timeout delay timer
timeOut VAR Bit ' timeout status
soT VAR Word ' temp counts from SHT11
tC VAR Word ' temp - Celcius
tF VAR Word ' temp - Fahrenheit
soRH VAR Word ' humidity counts
rhLin VAR Word ' humidity; linearized
rhTrue VAR Word ' humidity; compensated
status VAR Byte ' status byte
'

' EEPROM Data
'

'

' Initialization
'

Initialize:
GOSUB SHT_Connection_Reset ' reset device connection
PAUSE 250 ' let DEBUG window open
DEBUG CLS,
"SHT11 Sensor Demo", CR,
"

", CR
'

' Program Code
'

Main:
DO
GOSUB SHT_Measure_Temp
DEBUG CRSRXY, 0, 3,
"soT...... ", DEC soT, CR,
"tC....... ", DEC (tC / 10), ".", DEC1 tC, DegSym, " ", CR,
"tF....... ", DEC (tF / 10), ".", DEC1 tF, DegSym, " "
GOSUB SHT_Measure_Humidity
DEBUG CRSRXY, 0, 7,
"soRH..... ", DEC soRH, CR,
Parallax, Inc. • Sensirion SHT11 Sensor Module (#28018) • 07/2003 5
"rhLin.... ", DEC (rhLin / 10), ".", DEC1 rhLin, "% ", CR,
"rhTrue... ", DEC (rhTrue / 10), ".", DEC1 rhTrue, "% "
PAUSE 1000
LOOP
END
'

' Subroutines
'

' connection reset: 9 clock cyles with ShtData high, then start sequence
'
SHT_Connection_Reset:
SHIFTOUT ShtData, Clock, LSBFirst, [noparse][[/noparse]$FFF\9]
' generates SHT11 "start" sequence
' _____ _____
' ShtData |_______|
' ___ ___
' Clock ___| |___| |___
'
SHT_Start:
INPUT ShtData ' let pull-up take high
LOW Clock
HIGH Clock
LOW ShtData
LOW Clock
HIGH Clock
INPUT ShtData
LOW Clock
RETURN
' measure temperature
' -- celcius = raw * 0.01 - 40
' -- fahrenheit = raw * 0.018 - 40
'
SHT_Measure_Temp:
GOSUB SHT_Start ' alert device
ioByte = ShtTemp ' temperature command
GOSUB SHT_Write_Byte ' send command
GOSUB SHT_Wait ' wait for measurement
ackBit = Ack ' another read follows
GOSUB SHT_Read_Byte ' get MSB
soT.HighByte = ioByte
ackBit = NoAck ' last read
GOSUB SHT_Read_Byte ' get LSB
Parallax, Inc. • Sensirion SHT11 Sensor Module (#28018) • 07/2003 6
soT.LowByte = ioByte
' Note: Conversion factors are multiplied by 10 to return the
' temperature values in tenths of degrees
tC = soT ** $1999 - 400 ' convert to tenths C
tF = soT ** $2E14 - 400 ' convert to tenths F
RETURN
' measure humidity
'
SHT_Measure_Humidity:
GOSUB SHT_Start ' alert device
ioByte = ShtHumi ' humidity command
GOSUB SHT_Write_Byte ' send command
GOSUB SHT_Wait ' wait for measurement
ackBit = Ack ' another read follows
GOSUB SHT_Read_Byte ' get MSB
soRH.HighByte = ioByte
ackBit = NoAck ' last read
GOSUB SHT_Read_Byte ' get LSB
soRH.LowByte = ioByte
' linearize humidity
' rhLin = (soRH * 0.0405) - (soRH^2 * 0.0000028) - 4
'
' for the BASIC Stamp:
' rhLin = (soRH * 0.0405) - (soRH * 0.002 * soRH * 0.0014) - 4
'
' Conversion factors are multiplied by 10 to return tenths
'
rhLin = (soRH ** $67AE) - (soRH ** $83 * soRH ** $5B) - 40
' temperature compensated humidity
' rhTrue = (tc - 25) * (soRH * 0.00008 + 0.01) + rhLin
'
' Conversion factors are multiplied by 10 to return tenths
' -- simplified
'
rhTrue = (tC - 250) * (soRH ** $34) + rhLin
RETURN
' sends "status"
'
SHT_Write_Status:
GOSUB SHT_Start ' alert device
ioByte = ShtStatW ' write to status reg cmd
Parallax, Inc. • Sensirion SHT11 Sensor Module (#28018) • 07/2003 7
GOSUB SHT_Write_Byte ' send command
ioByte = status
GOSUB SHT_Write_Byte
RETURN
' returns "status"
'
SHT_Read_Status:
GOSUB SHT_Start ' alert device
ioByte = ShtStatW ' write to status reg cmd
GOSUB SHT_Read_Byte ' send command
ackBit = NoAck ' only one byte to read
GOSUB SHT_Read_Byte
RETURN
' sends "ioByte"
' returns "ackBit"
'
SHT_Write_Byte:
SHIFTOUT ShtData, Clock, MSBFirst, [noparse][[/noparse]ioByte] ' send byte
SHIFTIN ShtData, Clock, LSBPre, [noparse][[/noparse]ackBit\1] ' get ack bit
RETURN
' returns "ioByte"
' sends "ackBit"
'
SHT_Read_Byte:
SHIFTIN ShtData, Clock, MSBPre, [noparse][[/noparse]ioByte] ' get byte
SHIFTOUT ShtData, Clock, LSBFirst, [noparse][[/noparse]ackBit\1] ' send ack bit
INPUT ShtData ' release data line
RETURN
' wait for device to finish measurement (pulls data line low)
' -- timeout after ~1/4 second
'
SHT_Wait:
INPUT ShtData ' data line is input
timeOut = No ' assume no timeout
FOR toDelay = 1 TO 250 ' wait ~1/4 second
IF (ShtData = 0) THEN EXIT
PAUSE 1
NEXT
IF (toDelay = 250) THEN timeOut = Yes ' loop completed = timeout
RETURN
Parallax, Inc. • Sensirion SHT11 Sensor Module (#28018) • 07/2003 8
' reset SHT11/15 with soft reset
'
SHT_Soft_Reset:
GOSUB SHT_Connection_Reset ' reset the connection
ioByte = ShtReset ' reset command
ackBit = NoAck ' only one byte to send
GOSUB SHT_Write_Byte ' send it
PAUSE 11 ' wait at least 11 ms
RETURN
In high humidity applications, the SHT11 heater can be switched on briefly to prevent condensation.
Another use of the heater is to test the operation of the sensor: by reading before enabling the heater
and immediately after the sensor can be verified by noting a higher temperature and lower humidity.
The following subroutines can be used to switch the SHT11 heater on and off.
Heater_On:
status = %00000100 ' heater bit = On
GOSUB SHT_Write_Status
RETURN
Heater_Off:
status = %00000000 ' heater bit = Off
GOSUB SHT_Write_Status
RETURN

Matt K · 2007-05-31 18:50

The If Then code that I told you earlier was wrong.· I meant If tF > 80 or rhLin > 45.· The LEDs would come on when the temp or humidity was below 80 or 45%.·

Chris Savage · 2007-05-31 19:42

Matt,

In the future please attach larger programs like this one rather than pasting them. As for the conditional I was simply copying your example with the less than…Certainly if you want greater than you would change those symbols. The values you’re comparing against are not necessarily what you want as they include the integer and floating point parts of the value. You will need to convert the value to an integer or calculate the conditional in a different way.

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Chris Savage
Parallax Tech Support

Controlling 12V DC motor w/ sht11 temp. humidity sensor

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