Author Topic: Integrated temp/humidity sensor (Read 1500 times)

Jason_WI · « **on:** October 05, 2004, 05:10:36 pm »

I found an inexpensive integrated temp/humidity sensor from a European company. It has a 2 wire digital interface and is NIST traceable. It has a fairly large temp range and it has a heater to prevent condensation at high humidity levels.

http://www.sensirion.com/en/pdf/Datasheet_SHT1x_SHT7x.pdf

Of course you will need a microcontroller to get the data out of it.....

Useful for DIY controllers or monitoring equipment.

Jason

Den Socling · « **Reply #1 on:** October 05, 2004, 06:09:13 pm »

Hi Jason,

I see it's Swiss like the unit we use. Did you get the evaluation kit yet?

Den

Jason_WI · « **Reply #2 on:** October 05, 2004, 08:16:16 pm »

Den,

I have one working and reading back data as I type. Responce time is fairly fast. The heater works as it will raise the temperature slowly. Not sure how it will last in a kiln enviroment with the acids and dust. From the data sheet it looks like it survived some fairly harsh tests. Definately would have to pot the leads and coat the PCB with conformal to prevent the traces from corroding.

Your controllers use a 4-20 ma input? Do they have some sort of serial data input? If so then it might be possible to integrate one of these with a PIC processor to try out. They range from 25 to 30 bux depending on the accuracy required. Newark has them in stock.

Jason

Jason_WI · « **Reply #3 on:** October 05, 2004, 09:19:10 pm »

Here are a couple of pictures of the Sensirion Temp/RH sensor operating on my Basic Stamp dev system.

Here are some chunks of code that make it work:

' ------------------------------------------------------------------------------
' Subroutines
' ------------------------------------------------------------------------------

' connection reset: 9 clock cyles with ShtData high, then start sequence
'
SHT_Connection_Reset:
SHIFTOUT ShtData, Clock, LSBFIRST, [$FFF\9]

' generates SHT1x "start" sequence
'
'SHT_Start:
INPUT ShtData ' let pull-up take line high
LOW Clock
HIGH Clock
LOW ShtData
LOW Clock
HIGH Clock
INPUT ShtData
LOW Clock
RETURN

' measure temperature
' -- celcius = soT * 0.01 - 40
' -- fahrenheit = soT * 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 until measurement done
ackBit = Ack ' another read follows
GOSUB SHT_Read_Byte ' get MSB
soT.HIGHBYTE = ioByte
ackBit = NoAck ' last read
GOSUB SHT_Read_Byte ' get LSB
soT.LOWBYTE = ioByte

' Note: Conversion factors are multiplied by 10 to return the
' temperature values in tenths of degrees

tC = soT / 10 - 400 ' convert to tenths C
tF = soT ** 11796 - 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 until measurement done
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 * 0.004 * soRH * 0.0007) - 4
'
' Conversion factors are multiplied by 10 and then rounded to
' return tenths
'
rhLin = (soRH ** 26542)
rhLin = rhLin - ((soRH ** 3468) * (soRH ** 3468) + 50 / 100)
rhLin = rhLin - 40

' temperature compensated humidity
' rhTrue = (tC - 25) * (soRH * 0.00008 + 0.01) + rhLin
'
' Conversion factors are multiplied by 100 to improve accuracy and then
' rounded off.
'
rhTrue = ((tC / 10 - 25) * (soRH ** 524 + 1) + (rhLin * 10)) + 5 / 10
RETURN

' sends "status"
'
SHT_Write_Status:
GOSUB SHT_Start ' alert device
ioByte = ShtStatW ' write to status reg command
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 command
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, [ioByte] ' send byte
SHIFTIN ShtData, Clock, LSBPRE, [ackBit\1] ' get ack bit
RETURN

' returns "ioByte"
' sends "ackBit"
'
SHT_Read_Byte:
SHIFTIN ShtData, Clock, MSBPRE, [ioByte] ' get byte
SHIFTOUT ShtData, Clock, LSBFIRST, [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
FOR toDelay = 1 TO 250 ' give ~1/4 second to finish
timeOut = INS.LOWBIT(ShtData) ' scan data line
IF (timeOut = No) THEN SHT_Wait_Done ' if low, we're done
PAUSE 1
NEXT

SHT_Wait_Done:
RETURN

' reset SHT1x 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

beenthere · « **Reply #4 on:** October 05, 2004, 09:31:24 pm »

Jason
That is interesting. Need to study it a bit, to catch up on all it will do.

old3dogg · « **Reply #5 on:** October 09, 2004, 05:47:53 am »

Wow!That looks like some of the crap on my Trane 80 ton chiller.No one can figure it out.Not even the people from Trane

GregS · « **Reply #6 on:** October 17, 2004, 08:29:37 am »

Jason,
I was thinking it was not worth making my own kiln-contoller but you are influencing me to consider it. I like the sensor from what I see so far. I like the fact you could place the sensor in the bad environment and send the data serially to the controller.

Are you going futher with this and actually controling heating and DH units with your future home-brewed controller?

I do some HW/SW work all day so I would love to sneak in some kiln stuff along the way.

Thanks for sharing!

Greg

Den Socling · « **Reply #7 on:** October 17, 2004, 08:45:19 am »

I always said that Jason was a bad influence.

Den Socling · « **Reply #8 on:** October 17, 2004, 08:48:02 am »

Loop controllers have serial (RS485) and current inputs. All you have to do is assign units to the top and bottom of the span.

Jason_WI · « **Reply #9 on:** October 18, 2004, 11:35:36 am »

The sensor uses a 2 wire serial connection but uses a protocol similar to I^2C. A PIC or basic stamp could get the data from the sensor, convert it to a meaningful number then send it out either RS232 or 485 to a loop controller as a slave device.

Another option is to just use the PIC or basic stamp as a process controller by using band gap control or if needed full PID control.

Jason

GF · « **Reply #10 on:** October 19, 2004, 09:41:34 am »

Here is something I have been toying with with the remote temp and humidity sensors. Using it through cat 5, able to monitor kiln conditions via the internet.
http://www.apc.com/products/family/index.cfm?id=47

woodhaven · « **Reply #11 on:** October 19, 2004, 01:30:29 pm »

I did mine that way once just to prove to myself it would work. Bad thing is your computer will have to always be turned on and connected to the internet to get your readings. You would need a seperate phone line or someone to turn on the computer and do a dial up before you could read anything. It does work just fine but for me it was more trouble than it was worth. Now I just dial up into the system through any phone line.

Jason_WI · « **Reply #12 on:** October 19, 2004, 04:16:56 pm »

GF,

That system looks expensive

And a little overkill

Jason

Den Socling · « **Reply #13 on:** October 19, 2004, 04:23:49 pm »

As I've mentioned before, FDC's loop controllers come with free software that interfaces them via RS485 to a pc. Then, with pcAnywhere, you connect through a phone line or through the INTERNET to/from anyplace that has a connection.

loopy Den

woodhaven · « **Reply #14 on:** October 19, 2004, 05:57:42 pm »

Den,
Would you really recommend something like PcAnywhere ?
My experience with it has been its slow as a 12 year itch.

GF · « **Reply #15 on:** October 20, 2004, 08:45:19 am »

Den,
I am looking for something that will monitor the temp and humidity with remote probes, not really trying to control anything (yet). Something simple and reliable, and possibly digital, but still has to handle inside kiln extremes. Any ideas where I could find something like this?

Jason_WI · « **Reply #16 on:** October 20, 2004, 04:43:12 pm »

GF,

How long of a run for each sensor? Currently I have them on 12 feet of phone cord without any problems. I have PIC code for the above listed sensor. Currently monitoring 2 sensors and updates the LCD every 1/2 second and sends data out the RS232 serial port at 9600,8,N,1 about every minute. Currently the timing is fixed but that could be changed by adding a simple serial user interface.

These sensors haven't been proven in a kiln enviroment so there is some risk but I think it would be minimal.

I can come up with a cost if your interested.

Jason

Den Socling · « **Reply #17 on:** October 20, 2004, 09:35:40 pm »

Woodhaven,

pcAnywhere is slow with a dial up connection but, with a good connection, you don't see any difference in speed when connected to a remote computer.

Den

GF · « **Reply #18 on:** October 21, 2004, 06:50:06 am »

Jason_Wi
Its only about 7ft, I only have a solar kiln and thought it would be neat to monitor temp/humidity at top, and temp and humidity coming out the botton of the stack just to see what the moisture gain and temp loss is. Right now I have remote temp probes but not humidity.

GF · « **Reply #19 on:** October 21, 2004, 06:54:39 am »

TDK also makes a temp humidity probe/chip its a CHS-UGR, but I cannot find any specs on it.

Jason_WI · « **Reply #20 on:** October 21, 2004, 01:45:51 pm »

GF,

With the TDK sensor the circuit would need an A/D converter. Also the temp sensor needs to be mounted extremely close the the humidity sensor to correctly calculate the linearity of the humidity sensor and for calculating the dew point.

Here is the data sheet for the TDK sensor:

http://www.component.tdk.com/components/catlist/eb111_chs.pdf

Jason

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Author Topic: Integrated temp/humidity sensor (Read 1500 times)