Chapter 4. Modified Circuit; Introduction; The "Reduced Current" Circuit - Microchip Technology Humidity Sensor PICtail User Manual

4.1

INTRODUCTION

The modifications described here will reduce the current going into the integrator (I
by a factor of 100 ×, so the measurement resolution increases by the same factor.
These modifications are intended for measuring small capacitances. See AN1016 for
more details on this modified circuit's performance.
4.2

THE "REDUCED CURRENT" CIRCUIT

4.2.1
Figure 4-1 shows the Humidity Sensor PICtail™ Demo Board top silk-screen.
Figure 4-1 also shows the locations of the resistors that need to be modified to
implement the "Reduced Current" circuit discussed in application note AN1016:
1. Remove (de-solder) the 1Ω resistor, RA1, already on the board.
2. Refer to Appendix B. "Bill Of Materials (BOM)", Section B.3 for the BOM for
3. Solder RA1, RA2 and RA3 onto the board.
FIGURE 4-1:
© 2005 Microchip Technology Inc.
HUMIDITY SENSOR PICTAIL™
DEMO BOARD USER'S GUIDE

Chapter 4. Modified Circuit

Modifications
the three resistors (provided by the user) that need to be soldered onto the board.
- RA1 = 1 MΩ
- RA2 = RA3 = 20 kΩ
Resistor Modifications.
)
INT
resistors to
to modify
DS51594A-page 17