OM11055,598 - NXP Semiconductors

UM10370

User Manual for the PCF8883 Evaluation Kit OM11055

Rev. 02 — 2 December 2009 User manual

Document information

Info Content

Keywords Capacitive switch, sensor, proximit y s witch, PCF8883, OM110 55,

PCF8883 evaluation board

Abstract The OM11055 is a PCF888 3 evaluation board which can be used to

demonstrate and evaluate the PCF8883 ca pacitive proximity switch. The

PCB is designed to make it easy to adjust the switch’s sensitivity. The

board can be po wered using a Mini USB cable or a 9V battery.

NXP Semiconductors UM10370

PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 2 of 11

Contact information

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

For sales office addresse s, please send an email to: salesaddresses@nxp.com

Revision history

Rev Date Description

02 20091202 Fully updated version to reflect the change of the evaluation kit. Revision 1 was written for

the preliminary evaluation board which was marked “MA142_EVALBOARD.BRD”.

Revision 2 is valid for the ne w evaluation kit OM1105 5 (not marked as such on the board).

01 20090731 Initial release

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PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 3 of 11

1. Introduction

This user manual describe s the OM11055 evaluation kit. This board was develo ped in

order to provide a tool for application engineers and development engine ers wishing to

try and evaluate the single channel PCF 8883 capacitive proximity switch. A LED displays

the status of the switch; test points facilitate measurements of important signals.

The desired capacitive sensor area can vary in terms of material, form, size and

switching distance. Each particular swit ch configuration demands a suitable electrical

circuit for the input signal. This board allows to easily change the input circuit and the two

capacitors which defin e the sensitivity and reaction speed of the sensor in a typical

application. This offers the opportunity to rapidly evaluate many possible swit ching

configurations.

Features:

• Simple demonstration of the single channel PCF8883 capacitive proximity switch

• Jumper to select one of the three po ssible switch mod es of the PCF8883

• Evaluate different sensor size s (four different sensor plates included on the board) or

off board user defined sensors

• Two power supply options: via USB cable or a 9V bat tery

• Provisions for through-hole compo nents allowing them to be easily changed

• Contents of the kit:

− One PCF8883 evaluation board

− One 3 ft USB A-B Mini Cable

• All documentation is available from the NXP website:

http://www.standardics.nxp.com/support/boards/pcf8883

2. Quick start

The OM11055 is an evaluation board for the single channel PCF8883 capacitive

proximity switch.

1. Apply power to the board by connecting the sup plied mini USB cable to the PCF8883

board and the other end into a PC or a USB power adapter. Altern atively a 9V

battery can be used. The capacitive proximity sensor is now active.

2. With no jumpers on J9 (timed mode), touching the sense plate CP1 will turn on the

green output LED (LD1) for about two seconds.

Please read this manual completely for config uration options and modes.

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PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 4 of 11

3. Board description and layout

Below the top view of the board is shown.

Option to connect an

external sense plate

High impedance op-amp PCF8883

Sensor output connections Output LED, LD1

Setting of output time

Mini USB connector for power

Setting of switch mode

(Push-button, toggle or pulse)

Connection for 9V battery

Optional header to select sense plate

(defaults to CP1)

Four sense plates (selected by J6)

Fig 1. Top view of the PCF8883 evaluation board

The lower halve is dominat ed by four sensor areas of different size. The actual circuit is

on the upper halve of the board. Arrows indicate the parts of interest which are d escribed

more in detail in subsequent sections.

3.1 Setting the PCF8883 operation modes

The OM11055 allows the user to set one of three output switching behaviour modes,

using jumper J9. Refer to Fig 2:

a) With no jump er on J9, the PCF8883 will operate in pulse mode. Th e output is

activated for a defined time at each capacitive event. This defin ed time is

determined by C5.

b) With the jump er across the “TOG” and “TIM” pins, the PCF8883 will operate in

toggle mode (touch on, touch off).

c) With the jumper across the “SW” and “TIM” pins, the PCF8883 will operate in

momentary switch mode (push-button). The output is active as long as the

capacitive event lasts.

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PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 5 of 11

Fig 2. Selection of operating mode using jumper J9

4. User configurable settings

The OM11055 kit allows the user to conf igure the PCF8883 sensor for evaluation in a

specific application.

4.1 Sensor plate selection

The OM11055 board inclu des four sensor plates on the board itself and provisions to

connect the PCF8883 to an external sen sor. The board connects CP1 to the PCF8883

by default. To enable the other sensor options:

1. Cut the trace that shorts J6 pins 1 & 2 on the underside of the board.

2. Solder in a user supplied 8-pin header (0.1” pitch) at J6.

3. To select sensor plate CP4, conne ct a user-supplied jumper across J6, pins 7 &

8; to select CP3, jumper pins 5 & 6 of J6, etc.

To use an off board sensing plate, connect the plate at J14 & J18 using coax cable. The

coaxial shield must be connected to the input pin which is marke d ‘−‘. In this case do not

jumper any pins on J6.

Fig 3. Sensor plate selection

Cut trace under J6 to disable CP1

User can connect external

sensor at J14 & J18 using

coax cable

User can now add an 8pin header

and Jumper at J6 to select sensor

plates CP1 to CP4.

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PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 6 of 11

The size and form of the sensor plate ca n be varied to obtain optimal switching b ehaviour

or to shape the sensor for a given appli ca t ion.

The following figure shows some creative examples of how the switch can be used with

sensors of various size and shape.

Fig 4. Examples of sensor areas and shap es

4.2 Sensitivity settings

The OM11055 board allows for easy mo difications to the circuit to change the switch’s

sensitivity. It can be difficult to remove and install surface mount capacitors and resistors

without damaging the board. Therefore the OM11055 board includes holes to add

conventional through-hole passive components which enable quick evaluation of different

values. To remove the SMD component s R1 and C1 from the circuit, cut the trace shorts

on the underside of the PCB at J4 and J5. Refer to the PCF8883 datasheet and the

application note AN10832 for details on adju sting the sensitivity.

Fig 5. Traces to be cut for sensiti vity setting adjustmen t

Cut trace under J4 to disable R1

Cut trace under J5 to disable C1

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PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 7 of 11

4.3 Power supply options

Power to the OM11055 PCB can be supplied using a mini USB cable (provided) or a 9V

battery. The 9V battery connector can be removed and a use r provided po wer supply

could be connected at JP3 & JP4 for evaluation of a specific application. Using an

external power supply also allows for easy measuring of the power consumption.

Warning: There is no protection against reverse polarity of the external power supply.

4.4 High impedance op-amp

A high input impedance rail-to-rail input and output op-amp (U2) is included on the board

to measure the voltage at the CPC pin of the PCF888 3. A capacitor is connected

between pin CPC and Vss. The value of this capacitor is used to adjust the sensitivity of

the switch. Since this is a very high impedance node, measuring directly with a probe

would disturb the control loop. Therefore this voltage buffer has been included on the

board. By default, this op-amp is not connected, as it would add to power consumption

measurements. To enable U2, install two pin headers and jumper s at J12 and J16.

Remark 1: Always first provide power to op-amp U2 (jumper J12) before connecting the

input to pin CPC of the PCF8883 (J16). Reversing this sequence could result in a CMOS

latch up.

Remark 2: The capacitor CCPC must be a good quality X7R type to minimize charge

leakage.

5. Sensor adjustment

It is recommended to start the evaluation of the application using the pre-assembled

components on the board since these have typical values and were tuned for use with

the default connected sensor plate CP1. This should give an adequate response in most

cases. In cases where the switch do es not respond or responds unreliably, it is likely that

the input capacitance exceeds the specified input range. The voltage measured on CCPC,

via testpoint TP2, should ideally be approximately ½·VDDREG (note: ½·VDDREG which is half

the internally regulated supply voltage, not ½·VDD). The bias point can be optimized by

first changing CF (and possibly also RC) according to step 1 in the 5-step table below.

Once the switch works properly, further optimizations can be done by adjusting CCPC and

CLIN. Details concerning optimization of the biasing are given in application note

AN10832.

The circuit has three parameters that influence the switching behaviour. These are listed

below in order of their influence:

• Switch sensitivity, set by CCPC

• Calibration of the total capacitance o n the se nsor input using resistor RC and

capacitor CF

• Switching speed, set by CCLIN

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PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 8 of 11

Table 1. Optimizing step by step

Step Component Description Min Typ Max

1 CIN (CF) CIN is the total input capacitance (CSensor + Ccable + CF). CF should

be chosen such that CIN is about 30 pF. This can be checked by

measuring the voltage over CCPC which should then be about ½ VDD.

10 pF 30 pF 60 pF

2 RS R

S and CF form a low pass filter. The typical values are likely to be

correct for most applications. - 6.8 kΩ -

3 RC This resistance compensates large i nput capacitances (long coaxial

cable, larger sensor plate area). Smaller resistor values should be

used with larger input capacitances.

5 kΩ 39 kΩ 50 kΩ

4 CCPC C

CPC determines the sensitivity of the sensor. If the sensitivity is

increased, the possibilit y of incorrect s witching due to interfering

electrical fields is also incr eased. This parameter has a strong

influence on the switching characteristic.

90 nF 470 nF 2500 nF

5 CCLIN C

CLIN determines the internal sampling frequency and therefore the

reaction time of the switch. Smaller values of CCLIN correspond to

shorter reaction times. Shorter reaction times lead to increased

current consumption.

0 pF 22 pF 100 nF

6. Board schematic

On the next page the schematic of the Rev “A” OM11055 PCB i s sho wn. Revision “A” is

identified by the fact that there is no revision number on the PCB. The schemati c is also

available as a separate .PDF document on our web site . Make sure to check our website

periodically for updates.

7. References and resource URLs

The documents below provide further useful information.

1. PCF8883 product datasheet.

2. AN10832; PCF8883 – capacitive proximity switch with auto-calibration.

Table 2. Resource URLs

Item Resource Description and location

1 OM11055 eval kit

document package Includes:

• This document

• Board schematic and BOM

• Links to datasheets and application notes

• Location:

http://www.standardics.nxp.com/support/boards/PCF8883

2 PCF8883 webpage Links to the datasheets and applic ation notes

http://www.nxp.com/pip/PCF8883_1.html

NXP Semiconductors

PCF8883 Evaluation Kit OM110 55

UM10370

User manual

UM10370_2

Rev. 02 — 2 December 2009

9 of 11

Fig 6. Schematic of OM11055

NXP Semiconductors UM10370

PCF8883 Evaluation Kit OM110 55

User manual Rev. 02 — 2 December 2009 10 of 11

8. Legal information

8.1 Definitions

Draft — The document is a draft version only. The content is still under

internal review and subjec t to formal approval, which may result in

modifications or additions. NX P Semiconductors does not give any

representations or warranties as to the accuracy or completeness of

information included herein and shall have no liability for the consequences

of use of such information.

8.2 Disclaimers

General — Information in this document is believed to be accurate and

reliable. However, NXP Semiconductors does not give any representations

or warranties, expressed or implied, as to the accuracy or completeness of

such information and shall have no liability for the consequences of use of

such information.

Right to make changes — NXP Semiconductors reserves the right to make

changes to information published in this document, including without

limitation specifications and product descriptions, at any time and without

notice. This document supersedes and replaces all information supplied prior

to the publication hereof.

Suitability for use — NXP Semiconductors products are not designed,

authorized or warranted to be suitable for use in medical, military, aircraft,

space or life support equipment, nor in applications where failure or

malfunction of a NXP Semiconductors product can reasonably be expected

to result in personal injury, death or severe property or environmental

damage. NXP Semiconductors accepts no liability for inclusion and/or use of

NXP Semiconductors products in such equipment or applications and

ther efore s uch inclusion an d/or us e is for the c ustomer ’s own risk.

Applications — Applications that are described herein for any of these

products are for illustrative purposes only. NXP Semiconductors makes no

representation or warranty that such applications will be suitable for the

specified use without further testing or modification.

Export control — This document as well as the item(s) described herein

may be subject to export control regulations. Export might require a prior

authorization from national authorities.

8.3 Trademarks

Notice: All referenced brands, product names, service names and

trademarks are property of their respective owners.

NXP Semiconductors UM10370

PCF8883 Evaluation Kit OM110 55

Please be aware that important notices concerning this document and the product(s)

described herein, have been included in the section 'Legal information'.

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

For sales office addresses, email to: salesaddresses@nxp.com

Date of release: 2 December 2009

Document identifier: UM10370_2

9. Contents

1. Introduction .........................................................3

2. Quick start............................................................3

3. Board description and layout.............................4

3.1 Setting the PCF8883 operation modes ..............4

4. User configurable settings.................................5

4.1 Sensor plate selection........................................5

4.2 Sensitivity settings..............................................6

4.3 Power supply options.........................................7

4.4 High impedance op-amp....................................7

5. Sensor adjustment..............................................7

6. Board schematic .................................................8

7. References and resource URLs.........................8

8. Legal information..............................................10

8.1 Definitions ........................................................10

8.2 Disclaimers.......................................................10

8.3 Trademarks......................................................10

9. Contents.............................................................11

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