NXP Semiconductors OM11058 User manual

UM10720

User manual for the TFT touch demo board OM11058

Rev. 1 — 25 June 2013 User manual

Document information

Info Content

Keywords OM11058, PCA8885, PCF8885, capacitive touch sensor, touch on TFT,

touch foil

Abstract The OM11058 demonstrates the capabilities of the PCA8885 and

PCF8885 for touch on display by using a double-sided ITO touch foil with

a diamond matrix and two ICs cascaded for an 8 8 resolution on a 7 inch

TFT display

User manual Rev. 1 — 25 June 2013 2 of 16

Contact information

For more information, please visit: http://www.nxp.com

For sales office addresses, please send an email to: [email protected]

NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

Revision history

Rev Date Description

v.1 20130625 new user manual, first revision

User manual Rev. 1 — 25 June 2013 3 of 16

NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

1. Introduction

Interactive user interfaces like in smartphones have become a must also in automotive,

industrial and white goods control units.

Unlike smartphones where multi-touch, drag and drop and zooming features are used, the

dedicated user interfaces in, for instance climate control or washing machine, only have to

be a replacement of mechanical buttons by on-display touch buttons. Accordingly, the

hardware- and software-design should be as simple as possible.

The PCA8885 and PCF8885 are providing very suitable features for easy configuration,

connection of various numbers of channels, optimization of sensitivity and sampling for

each application.

The purpose of the OM11058 is to demonstrate the capabilities of the PCA8885 and

PCF8885 for touch displays.

1.1 The PCA8885 and PCF8885 multi-channel capacitive proximity

sensors

The PCA8885 and PCF8885 are capacitive 8-channel touch and proximity sensors

detecting changes in capacitance on remote sensing plates. Changes in the static

capacitances (as opposed to dynamic capacitance changes) are automatically

Fig 1. OM11058 demo board

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NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

compensated using continuous auto-calibration. Remote sensing plates (for example,

conductive foils) can be connected to the IC. The eight input channels operate

independently of each other. There is also a built-in option for a matrix arrangement of the

sensors: interrupts are generated only when two channels are activated simultaneously,

suppression of additional channel outputs when two channels are already active.

Key features of the PCA8885 and PCF8885 are:

•Eight independent channels (can be configured as 4 4 matrix)

•I2C-bus interface

•One subaddress to enable up to 64 keys, cascading 2 devices

•Sleep mode, activated via I2C-bus or external input

•Three sensing modes: one key, two keys and n-keys

•Two event handling modes: direct and latching mode

•Adjustable scan frequency

•Channel masking feature

•Fast start-up mode

•Operating temperature range (Tamb = 40 C to +85 C)

•TSSOP28 and SO28 package available

•PCA8885: AEC-Q100 compliant for automotive and harsh environment applications

Fig 2. Block diagram of PCA8885 and PCF8885

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User manual Rev. 1 — 25 June 2013 5 of 16

NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

2. Description and technology of OM11058

The OM11058 block diagram is shown in Figure 3.

Fig 3. Block diagram of the OM11058

LPC1788

Developmentkit

7” TFTdisplay

13 x 21 linediamond

structure on two

layers

OM11056

2 x PCA8885evaluation board

Interconnection board for FPC

UM10720_01

User manual Rev. 1 — 25 June 2013 6 of 16

NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

2.1 Display layers

The basic building elements of - for example - a passive LCD are shown in Figure 4.

The touch sensor pads can be placed on the same layer as the display ITO as an

interleaved pattern (in-cell) or on top of the display glass, sandwiched under the polarizer

(on-cell), see Figure 5.

Fig 4. LCD layers

incident light

Segments:

Segments – Top ITO

Liquidcrystal molecules

Polarizer

Displayglass-Top

Common–Bottom ITO

Polarizer

transparent opaque

UM10720_03

User manual Rev. 1 — 25 June 2013 7 of 16

NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

The features of an in-cell stack are:

•Segment and touch ITO patterns are made in the same process step

•Lower LCD module cost

•Limited number of touch buttons can be made

For the OM11058, a separate foil with top and bottom ITO layers is used.

2.2 Touch panel

For the touch layer on the TFT display in the OM11058, a separate double sided touch foil

with 21 13 diamond matrix structure was taken as an off-the-shelf product.

a. On-cell touch stack b. In-cell touch stack

Fig 5. Touch display technology

Glass

ITO Layer Touch

Polarizer

ITO Layer

Segment

LiquidCrystal

UM10720_04

Glass

Polarizer

ITO Layer

Segment+Touch

LiquidCrystal

UM10720_05

Available vertical and horizontal lines:

13 21 = 273 points resolution 8 8 lines provide 64 touch buttons of which 16 are

used for the OM11058

Fig 6. 7- inch touch panel

76543210

IC#2

IC#1

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NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

If the sensor pads are organized in a matrix layout such as a foil with horizontally

connected diamond pads on one side and vertically connected diamond pads on the other

side, the sensor inputs of a single IC can be used for a 4 4 matrix as shown in Figure 7.

For larger matrices two PCA8885 packages can be cascaded as shown in Figure 8 to

locate the XY position of a touch.

Fig 7. 4 4 matrix layout

Bottomlayer Toplayer



UM10720_08

User manual Rev. 1 — 25 June 2013 9 of 16

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User manual for the TFT touch demo board OM11058

Fig 8. Cascaded application diagram

IN[0]

IN[1]

IN[2]

IN[3]

IN[7]

VDD

VDD(INTREGD)

100 nF

TEST

VSS

CPC[0] CPC[7]

SCL

SDA

CLK_IN

INT_IN

CLK_OUT

INT

SLEEP

PCA8885

IN[0]

IN[1]

IN[2]

IN[3]

IN[7]

VDD

VDD(INTREGD)

100 nF

TEST

VSS

CPC[0] CPC[7]

SCL

SDA

CLK_IN

INT_IN

CLK_OUT

INT

SLEEP

PCA8885

SENSOR MATRIX

(primary)

(secondary)

VDD

RPU

100 nF

RPU

to MCU

VDD

100 nF

VDD

100 nF

CCPC[0]

100 nF

CCPC[7]

100 nF

CCPC[0]

100 nF

CCPC[7]

(1)

(3)

013aaa581

(2)

User manual Rev. 1 — 25 June 2013 10 of 16

NXP Semiconductors UM10720

User manual for the TFT touch demo board OM11058

3. Quick start

3.1 Power supply

•The OM11058 is shipped with a USB cable. The USB supply port should be able to

source 2.5 A. Using the USB connector is also the option giving the highest sensitivity.

•Alternatively aAC/DC power adapter (5 V, >2.5 A) can be used. Preferably the power

adapter should be a linear converter. If a switching mode AC/DC converter (SMPS) is

used, it should be a three-pin connector with protective earth.

The supply connectors of the OM11058 are shown in Figure 9.

3.2 Operation

•When powering up, it takes about 30 seconds to get the touch operational due to the

delays in the start of the MCU evaluation board in order to get right sequence of

interrupts and I2C communication.

•All buttons are implemented as single switches.

CAUTION

This device needs a USB source that is able to handle 2.5 A. Ensure that the USB supply

connection is able to provide this amount of power. Otherwise, damages may occur.

Fig 9. Supply connectors

USB or power jack for

supply connecon

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