Humidity Sensor HS1101

sparks5

I have just installed the HS1101 and the Relative Humidity at the debug terminal reads 11%.
Present weather outside is overcast, rain and quite humid. Would a change in resistors 220ohm
and 10M ohm give a more realistic reading?
sparks5

JLocke

Is the sensor inside or outside? Although 11% is pretty low, even for inside your house. I have a couple of Sensiron temp/humidity sensors in a project, and they typically read in the 30%-40% range inside the house (even if it's raining outside).

Jessica Uelmen

Hi sparks5,

Since the HS1101 is essentially a capacitive cell, some calibration may need to be done in different operating environments. You shouldn't need to change the resistor values, as the 10 M-ohm resistor was chosen based on the sensor's nominal capacitance.

You can find calibration information in the HS1101's product documentation.

Or, check out the datasheet for additional wiring options.

Either way, let us know if you have any other questions!

Cheers,
Jessica

sparks5

Hi again:
Thanks for the reply, the sensor is indoors. Reducing the RHconstant increases the RH or leaving the RHconstant alone and dividing the equation by 6 increases the RH from 12% to 56% which is more
realistic. I guess I will have to borrow a hygrometer to calibrate the sensor more accurately.
Maybe Jessica can let me know where the RHconstant figure 12169 comes from and what am I doing when I alter that figure and the division figure.
p.s. Jessica I enjoyed your Christmas Caroling

Publison

Hi Sparks,

You never mentioned which chip you are using with the sensor. The R/c time can vary with different MCU's.

While this sensor is compatible with all Parallax microcontrollers, the included source code is solely for
BASIC Stamp®
2 microcontroller. When working with other BASIC Stamp models, a scale factor will have Copyright © Parallax Inc. HS1101 Relative Humidity Sensor (#27920) v1.0 4/13/2009 Page 4 of 4
to be applied to your code to account for different clock speeds. (For more information see the RCTIME
command in the BASIC Stamp Syntax and Reference Manual.)
Additional calculations and coding techniques will be required when interfacing with any other Parallax
microcontroller, since RCTIME is specific to the PBASIC programming language for BASIC Stamp
microcontroller modules.
Additional Spin programs have been developed to measure decay time and capacitance with the Propeller
chip. Use these programs in conjunction with performing additional control tests to develop Propeller
applications. Go to forums.parallax.com -> Propeller Chip -> Propeller Education Kit Labs for more
information.

Quote from:

http://www.parallax.com/Portals/0/Downloads/docs/prod/sens/27920-HS1101-v1.0.pdf

sparks5 wrote: »

Hi again:
Thanks for the reply, the sensor is indoors. Reducing the RHconstant increases the RH or leaving the RHconstant alone and dividing the equation by 6 increases the RH from 12% to 56% which is more
realistic. I guess I will have to borrow a hygrometer to calibrate the sensor more accurately.
Maybe Jessica can let me know where the RHconstant figure 12169 comes from and what am I doing when I alter that figure and the division figure.
p.s. Jessica I enjoyed your Christmas Caroling