Digilent 410-247P-KIT Bedienungsanleitung PDF herunterladen

CDC1

™

Capacitance-to-Digital Converter

Reference Manual

Revision: October 4, 2012

1300 Henley Court | Pullman, WA 99163

(509) 334 6306 Voice and Fax

Doc: 502-247 page 1 of 2

Overview

The PmodCDC1 demonstrates capacitance-to-

digital proximity sensing through two “buttons.”

Digilent engineers designed and built this

Pmod around the Analog Devices AD7156

Capacitance – to – Digital Converter.

Features include:

 I

C™ communication interface

 two capacitance input channels

 adaptive proximity threshold

Functional Description

The PmodCDC1 has two capacitive buttons for

user input and two output pins on header J2

that signal when they reach a proximity

threshold. (See Table 1) The PmodCDC1

measures this threshold in capacitance, the

users can program the threshold, and it can be

either positive or negative. A logic high output

on header J2 will indicate which channel has

reached its threshold.

Table1. Interface Connector Signal Description

Capacitance to Digital Conversion

The PmodCDC1 uses the AD7156 to measure

the capacitances of the two channels

separately by exciting the capacitance and

sampling the response. It stores data as a 16-

bit word that you can read by accessing the

correct data registers via I

C in the AD7156.

The PmodCDC1 averages the capacitance of

each channel, which allows users to configure

the PmodCDC1 to adapt its threshold level.

The adaptive threshold is a programmable

feature of the AD7156.

For more detailed information on controlling

the AD7156, please see the device’s data

sheet, available from www.analog.com.

C Interface

The Analog Devices AD7156 acts as a slave

device using I

C communication protocol. The

following instructions provide procedures for

reading and writing to the device.

The host device is the master when reading

from the PmodCDC1. If the host device

acknowledges the receipt of data, then the

AD7156 will auto increment the address

pointer and send the next byte of data in its

memory. The host device must assert a No

Acknowledge to the PmodCDC1 to cease

receiving data.

When reading a conversion value, assert an

Acknowledge between the first and second

byte in order to receive the bytes back to back.

Receiving them back to back will ensure that

data is not skipped between conversions.

Writing to the device is similar to reading from

it. After sending the first data byte, the address

pointer in the AD7156 will auto increment. If

the master sends another byte, then the

Connector J2 – AD7156 Output Pins

Pin Signal Description

1 OUT1 Threshold detected on CIN1

2 OUT2 Threshold detected on CIN2

1 2

Inhaltsverzeichnis

Seite 1 - Functional Description

PmodCDC1™ Capacitance-to-Digital Converter Reference Manual Revision: October 4, 2012 1300 Henley Court | Pullman, WA 99163 (509) 334 6306 Voice a

Seite 2 - Register Addresses

PmodCDC1 Reference Manual www.digilentinc.com page 2 of 2 Copyright Digilent, Inc. AD7156 will store that byte in this location and it will in

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Digilent 410-247P-KIT Bedienungsanleitung

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