E401 KIT Atmel, E401 KIT Datasheet - Page 8

• Manufacturer Part Number: E401 KIT
• Description: KIT EVAL FOR QT401-IS QSLIDE
• Manufacturer: Atmel
• Series: Quantumr

Specifications of E401 KIT

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 427-1084

BOARD DETAILS
6
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.
See Table 1 (next page) for a description of the connector pinout.
Voltage Regulator
The E401 uses a low drop out regulator to regulate the 5V coming from the USB adapter box
down to 3.3V. Resistor R25 is used to provide a minimum load on the regulator when the QT401
goes to sleep between acquisitions; this is necessary for regulator transient stability.
Since the QT401 works on a lower voltage (3.3V) than the USB box (5.0V), the signals from the
USB box to the E401 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.
Slider Element
The capacitive slider consists of the 17 resistors R2...R18 and the copper pads they connect.
The end–to-end resistance of the slider element is about 95K ohms. Resistors R1 and R19 are
zero ohms but can be changed to allow manual trimming of the end-positions of the slider if
adaptive calibration is not used. Increasing R1 and/or R19 will move the ends outwards.
Sampling Capacitors
C1 and C2 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.