PIC16F690DM-PCTLHS Microchip Technology, PIC16F690DM-PCTLHS Datasheet - Page 23

• 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

A.1
A.2
A.3
© 2005 Microchip Technology Inc.
INTRODUCTION
HIGHLIGHTS
DEMONSTRATION BOARD DESCRIPTION
This appendix contains the schematics and layouts for the Humidity Sensor PICtail™
Demo Board.
The Humidity Sensor PICtail™ Demo Board is constructed using a two-layer Printed
Circuit Board (PCB). The top layer is for components and traces. The bottom layer is
the ground plane.
Information on this board includes:
• Board Schematic
• Board – Top Silk-screen
• Board – Top Metal Layer
• Board – Bottom Metal Layer
A schematic is shown in Figure A-1 and Figure A-2. Csen is the humidity sensor or
capacitor. Op amp, U2, and the components, Csen and R
form an inverting (Miller) integrator. The jumpers, JP1 – JP3, select the R
choice (6.65 M , 665 k
(0.1 pF / count, 1 pF / count or 10 pF / count). The microcontroller, U1, sends a square
wave at its pin 14 to the input of the integrator. The integrator converts it to a triangle
wave, which is seen at the microcontroller’s pin 15. There is a comparator internal to
U1 which compares the voltage at pin 15 to one of two reference levels; V
V
each time the triangle wave exceeds one of these two limits.
The microcontroller (U1) measures the time between changes in logic values at pin 14
(“integration times”), and calculates a capacitance value for Csen. This capacitance
value (C
sensor. C
them to the capacitance.exe PC program on the PC via the USB cable.
RA1 – RA3 are used for the “Op Amp Integrator with Reduced Current” described in
AN1016 and Chapter 4. “Modified Circuit”. Rcm1, Rcm2 and Ccm provide a
mid-supply reference voltage for the op amp, U2.
Appendix A. Schematic and Layouts
DD
Note:
or V
SEN
RH
SEN
Converting Csen to RH for other humidity sensors must be done either
manually or by modifying the PIC16F690 firmware (i.e., the linear
interpolation table).
= 0.500 V
) is converted to Relative Humidity (RH) for Humirel’s HS1101LF humidity
and RH are then sent to the PICkit™ 1 Flash Starter Kit, which sends
DD
. The microcontroller changes the logic value output at pin 14
or 66.5 k ), which sets the measurement resolution
HUMIDITY SENSOR PICTAIL™
DEMO BOARD USER’S GUIDE
INT
(Rint1, Rint2 or Rint3),
DS51594A-page 19
INT
RL
value of
= 0.125