E3B Atmel, E3B Datasheet - Page 2

• Manufacturer Part Number: E3B
• Description: BOARD EVAL FOR QT310 & QT320
• Manufacturer: Atmel
• Series: Quantumr
• Type: Capacitive Touch and Proximity Sensorr

Specifications of E3B

• Rohs Status: RoHS non-compliant
• Contents: Evaluation Board
• For Use With/related Products: QT310, QT320
• Other names: 427-1056

Batteries
Board
Use 2x AAA alkaline batteries for best performance. External power may be used if the
Details
batteries are removed. Power consumption depends on the operating mode chosen.
Power Connections
The provided connection points (+PWR, GND) can be used to power the board. The
voltage should be between +2.5 and +5 volts DC, regulated. Power should be free from
switching noise and short-term fluctuations for best performance. Almost any linear
regulator will work. Be sure not to share this power with other circuits that may inject
noise or supply fluctuations into the board, as erroneous operation will result (example:
relays, digital logic, etc). If external power is used, be sure to remove the batteries.
'Out' Connections
The Out pins (Out1, Out2) are driven directly by the Out pins of the IC. Be careful not to
load these pins excessively, keeping source or sink current to under 2mA. The onboard
LED is also driven from this line (see schematic diagram). Depending on the cloned
Setups of IC, this output may be active high or active low.
It is not advised to connect an external pullup resistor to a voltage source other than
the same source powering the board. An external voltage source can back-feed the
board with current and attempt to charge the batteries via the internal clamp diodes in
the device, and in general is not good practice.
'Ext' Sense Connector Pads
These pins (EXT1, EXT2) provide a way to connect the device to external sensing
electrodes. The load should have low capacitance (Cx) for best results. High Cx will
decrease apparent sensitivity. Shielded cable can be used over limited distances,
usually with an increase in C1 and/or C2 to compensate for the increased Cx loading.
C1 / C2 Capacitors
The C1 and C2 capacitors (referred to generically as Cs or ‘sample’ capacitors) are
socketed and can be replaced for experimentation. Generally, higher values of Cs will
increase sensitivity. This increase is proportional to Cs. Use decent grade capacitors
(avoid cheap ceramic capacitors in favor of plastic film types or at worst, X7R 5% types
for best results). A typical minimum total value of Cs is 2nF on this board.
C3 Balance Capacitor
The C3 balance capacitor exists to balance the sensitivity of the two sensing channels
to make them equal. Without this capacitor, Sensor 1 will appear more sensitive than
Sensor 2. The inequality can be used to advantage in some applications. The other
methods of making the channels appear equal include a) reducing C1 relative to C2,
and b) changing the trip-point threshold via the cloning process (or both in conjunction).
C3 is a 5pF capacitor which can also be implemented by intentionally adding some stray
Cx to channel 1.
R3 / R4 Series Resistors
These resistors are used to reduce the currents induced by ESD transients to safe
levels. They also roll off the edges of the QT pulses thus reducing RF harmonics to an
even lower level. The values are not critical but they should not be so large that they
interfere with sensing. Typical values range from 1K to 47K. When connecting the EXT
pins to a larger Cx load, it may be necessary to reduce one or both of these resistances.
If a lowering of the resistor increases sensitivity, the resistor value is too high.
LEDs
The LEDs are driven directly from the IC. Depending on whether the output(s) have
been configured as active-low or active high, the LEDs may be normally off or on
respectively.
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