PIC16F690DM-PCTLHS Microchip Technology, PIC16F690DM-PCTLHS Datasheet - Page 11

• Manufacturer Part Number: PIC16F690DM-PCTLHS
• Description: BOARD DEMO PICTAIL HUMIDITY SNSR
• Manufacturer: Microchip Technology
• Series: PICtail™r

Specifications of PIC16F690DM-PCTLHS

• Sensor Type: Humidity
• Sensing Range: 1 ~ 99% RH
• Interface: Analog
• Voltage - Supply: 5V
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: MCP6291, PIC16F690
• Processor To Be Evaluated: MCP6291 and PIC16F690
• Interface Type: ICSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AC162061 - HEADER INTRFC MPLAB ICD2 20PIN
• Sensitivity: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

Calibration
Capacitive relative humidity sensors are quite sensitive
to capacitive measurement errors. It can be costly to
use components with tighter tolerances. The designs in
this application note are a big help because they have
low parasitic capacitance in parallel with the sensor,
and they are immune to sensor case to ground
capacitances.
The most effective way to overcome the sensitivity
problem is to calibrate the errors in production. All of
the errors can be corrected in the same step.
Miscellaneous
Using dual slope integration minimizes errors due to
the V
The op amp’s gain-bandwidth product affects the
relative error for small C
that gives an acceptable error at the smallest C
value that will be measured.
R
implement. It is chosen so that B
convenient number (e.g., 0.1 pF / count).
It is important to use a greater number of bits for the
averaging (accumulation) of C
design is a 16-bit value, and the accumulator is a 24-bit
value. This avoids truncation errors, and can prevent
counter results being interpreted as negative values.
SUMMARY
This application note shows hardware and firmware
design
microcontroller and an op amp integrator to accurately
measure small capacitances. Simple firmware is
included that produces capacitance and relative
humidity values for the HS1101LF relative humidity
sensor.
Measurements verify the theory and design choices.
An error analysis points to possible improvements in
the design. Other alternatives and modifications to this
design are also covered. Key lessons learned help the
user focus on the important aspects of the given
design.
The
information that supports the text of this application
note.
© 2005 Microchip Technology Inc.
INT
CM
is selected last to make the code simpler to
references
error (I
engineers
INT
imbalance).
and
how
SEN
appendices
values. Select an op amp
to
SEN
use
. The counter in this
1
a
give
becomes a
PICmicro
detailed
SEN
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REFERENCES
Humidity Sensors
[1] Humirel, “Relative Humidity Sensor HS1100LF /
General Sensors
[2] “The OMEGA
[3] “The OMEGA
[4] AN866, “Designing Operational Amplifier Oscilla-
[5] AN990, “Analog Sensor Conditioning Circuits – An
[6] AN512, “Implementing Ohmmeter/Temperature
[7] AN895 “Oscillator Circuits For RTD Temperature
Capacitive Sensors
[8] AN611, “Resistance and Capacitance Meter
[9] Ricardo Jimenez and Claudia Angulo, “Measure
[10] AN1014, “Measuring Small Changes in Capaci-
Related Literature
[11] AN942, “Piecewise Linear Interpolation on PIC12/
[12] MCP6291/2/3/4/5 Data Sheet, “1.0 mA, 10 MHz
[13] PIC16F685/687/689/690 Data Sheet, “20-Pin
[14] PIC16C745/765 Data Sheet, “8-Bit CMOS Micro-
[15] “Humidity Sensor PICtail™ Demo Board User’s
HS1101LF,” Data Sheet, Rev. C, Sept. 2004.
Vol. 1, OMEGA Engineering, Inc., 2002.
Vol. 2, OMEGA Engineering, Inc., 2002.
tor
Lepkowski; Microchip Technology Inc., DS00866,
2003.
Overview”, Kumen Blake, Microchip Technology
Inc., DS00990, 2005.
Sensor”, Doug Cox; Microchip Technology Inc.,
DS00512, 1997.
Sensors”, Ezana Haile and Jim Lepkowski;
Microchip Technology Inc., DS00895, 2004.
Using a PIC16C622”, Rodger Richey; Microchip
Technology Inc., DS00611, 1997.
Relative Humidity With a PIC
Briefs, Electronic Design, March 17, 2005, p. 79-
80.
tive Sensors”, Kumen Blake and Steven Bible;
Microchip Technology Inc., DS01014, 2005.
14/16 Series Microcontrollers”, John Day and
Steven Bible; Microchip Technology Inc., 2004.
Rail-to-Rail Op Amp,” Microchip Technology Inc.,
DS21812, 2004.
Flash-Based, 8-Bit CMOS Microcontrollers with
nanoWatt Technology”, Microchip Technology Inc.,
DS41262, 2005.
controllers with USB”, Microchip Technology Inc.,
DS41124, 2000.
Guide”, Microchip Technology Inc., DS51594,
2005.
Circuits
®
®
For
Made in the USA Handbook™”,
Made in the USA Handbook™”,
Sensor
AN1016
Applications”,
DS01016A-page 11
®
MCU”, Design
Jim