E3A EVALUATION BOARD USER'S GUIDE
for use with QT300 QProx™ sensor IC
Overview
Fast Start
The E3A board works with Quantum's
QT300 16-bit Capacitance to Digital
Converter (CDC) sensor IC. The device
can be inserted into the 8-pin DIP socket
at the front of the board.
QT300 - serial communications interface
(16 bit data).
For detailed information about this IC
please refer to the QT300 datasheet.
See Figure 2, page 4 for component and
connector identification.
Note: references on the PCB to the
QT301 should be ignored. It is not
available because it is not RoHS compliant.
To begin using the board:
1. Make sure the power switch is 'off'. Insert a 9V alkaline battery into the holder.
2. Ensure that the DEVICE jumper (bottom right corner of board) is set to the QT300.
3. Make sure the MODE jumper is set to ACTIVE.
4. Turn on the power switch.
5. Calibrate the E3A to your finger as a simple test. While not touching any other part
of the E3A:
a. Keeping your hand away from the Sensor pad, press the LOWER button using a
plastic pen or pencil.
b. Put a finger lightly on the middle of the Sensor pad and press the UPPER button
using a plastic pen or pencil.
6. Slide your finger from the lower left corner of the board towards the middle of the
Sensor pad area; you will observe the change in signal strength on the LCD. Refer
to the 'LCD Display' section, page 3 for more information.
Because of Kirchoff's Current Law ("all currents must return to their origin", which
also applies to capacitive fields), the sensor is less sensitive if you are not holding it
or if the board's ground is not electrically coupled to something else. Thus, placing
the board on your desk will result in less sensitivity than if you hold it by the batteries
or connect the board's ground to something larger (or to earth ground).
Touching the cal buttons with your finger while pressing them, while on battery
power, will cause an undesirable offset to the calibration. If the E3A is externally
powered, this effect will not occur.
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Board
Details
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Schematic Diagram
Please refer to the schematic diagram in this guide.
Batteries
Use a 9 Volt Alkaline for best performance.
Remove batteries when using external power!
External Power Connections
Connector J1 can be used to power the board. The voltage should be between +8 and
+12 volts DC. Power should be free from switching noise and short-term fluctuations
for best performance.
WARNING: External power - please note! Be sure to remove the batteries first, or
you may cause an explosion and leakage hazard as the batteries will try to charge up
from the external supply!
Device Jumper
Ensure that the jumper is set to the QT300 device (see the note in Overview, page 1
about the nonavailability of the QT301).
Mode Jumper
This jumper allows you to switch the LCD controller to either the ‘active’ or ‘passive’
mode.
Active mode: The LCD controller will drive the QT300 and display the data on the
LCD. To work correctly the QT300 needs to be set to ‘slave’ mode using setups from
a PC (using a QTM300CA board + QT3View software for example).
Passive mode: In this mode the LCD controller ‘sniffs’ data transfers on the SPI lines.
If the E3A is connected to an external host (like a QTM300CA board, or your own host
microcontroller), the LCD will display data as requested by the host.
Sensor Circuit
C1 Capacitor (referred to generically as the Cs or ‘sample’ capacitor) is socketed and
can be replaced for experimentation. Higher values of Cs increase sensitivity, in direct
proportion. Use decent grade capacitors (avoid cheap ceramic capacitors in favor of
plastic film types or at worst, ceramic X7R 5% types for best results). A typical
minimum usable value of Cs is 2nF (0.002uF, or 2,000pF).
'Ext' Sense Connector provides a way to connect the chip to an external sensing
electrode or fluid level probe. The load should have low baseline capac itance (Cx) f or
best results. High Cx will decrease apparent sensitivity, perhaps requiring an increase
in Cs to compensate. Shielded cable can be used over lim ited distances, usually with
an increase in Cs to compensate for the increased Cx loading.
Sensor Select Switch connects the sense pin of the device to either the sense pad or
the external connector. UP = internal pad; DOWN = external connector.
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