7
BOARD DETAILS
SPI Interface Connector
This connector provides all signals and power needed to communicate with the USB adapter or
an external host such as a microcontroller.
If you wish to connect the E510 to a microcontroller and operate the QT510 in
sleep mode
you
will need to provide in your interface circuit a 1nF capacitor between PROX (CON1 pin 9) and
GND, and a 22k Resistor between DRDY (CON1 pin 4) and GND. Refer to the QT510 Datasheet
for more information.
See
Table 1
(next page)
for a description of the connector pinout.
Voltage Regulator
The E510 uses a low drop out regulator to regulate the 5V supply from the USB adapter box to
3.3V. Resistor R25 is used to provide a minimum load on the regulator when the QT510 sleeps
between acquisitions; this is necessary for regulator transient stability.
Since the QT510 works on a lower voltage (3.3V) than the USB box (5.0V), the signals from the
USB box to the E510 must be level shifted down. This is done using resistive dividers consisting
of 1K resistors R20, R21 and R22, plus a set of 560 ohm resistors placed in series with the signal
lines inside the USB box.
Rotary Slider Element
The capacitive rotary slider consists of 18 resistors R1...R18 and the copper pads they connect
to. Resistors R19, R23 and R24 provide the QT510 with ESD protection.
Sampling Capacitors
C1 C2 and C5 are the Cs sampling capacitors; increasing their value will increase sensitivity and
resolution of measurement, but will also tend to make for a slower response time.
