ST STM32F0 Series, STM32F3 Series, STM32L0 Series, STM32L1 Series, STM32L4 Series Application Note

AN5105

Application note

Getting started with touch sensing control on STM32 microcontrollers

Introduction

This document helps customers to quickly locate information regarding touch sensing on STM32 microcontrollers.

It is applicable to STM32F0, STM32F3, STM32L0, STM32L1 and STM32L4 Series products. It lists all the existing application
notes and user manuals covering touch sensing. It indicates where the key aspects of touch sensing are documented.

It also explains how to build touch sensing applications on STM32L0538-DISCO and STM32F072B-DISCO discovery boards
using the STM32CubeMx graphical interface.

AN5105 - Rev 1 - September 2018
For further information contact your local STMicroelectronics sales office.

www.st.com

1 General information

This document applies to Arm®-based devices.

Note: Arm is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.

AN5105

General information

AN5105 - Rev 1

page 2/52

2 Terminology and principle

2.1 Terminology

The touch sensing most relevant acronyms are described below:

• Acquisition mode

– CT: Charge-Transfer acquisition principle. This mode is used on STM32 microcontrollers.

• Touch sensing STM32 peripheral

– TSC: touch sensing controller peripheral

– Bank: set of channels acquired simultaneously

– Channel: elementary acquisition item

– Group: set of 1..3 channels plus 1 sampling capacitor (Cs)

• Sensors

– Touchkey or TKey: single channel sensor

– Linear sensor: multi-channels sensor with the electrodes positioned in a linear way

– Rotary sensor: multi-channels sensor with the electrodes positioned in a circular way

– Active shield: track running along or copper plane surrounding the sensor track and/or sensor itself.

Active shield is driven similarly to the sensor. Improve noise robustness without decreasing the
sensitivity.

• STM32 software

– TSL: touch sensing library

– Delta: difference between the measure and the reference

– Measure or meas: current signal measured on a channel

– Reference or ref: reference signal based on the average of a sample of measures

– DTO: detection time out. Time out is defined by TSLPRM_DTO. See TSLPRM_DTO in tsl_conf.h file.

– DXS: detection exclusion system. Exclusion system is defined by TSLPRM_USE_DXS. See

TSLPRM_USE_DXS in tsl_conf.h file.

– ECS: environment change system. See TSLPRM_ECS_DELAY in tsl_conf.h file.

• Hardware Involved

– Cx: sensor capacitance (typical value is few pF)

– Cp: parasitic capacitance (typical value few pF)

– Ct: equivalent touch capacitance

– Cs/Cskey/Csshield: sampling capacitor (typical value from 2.2 to 100nF)

– Rs/Rskey/Rsshield: serial resistor, ESD protection (typical value from 100Ohms to 10K)

AN5105

Terminology and principle

2.2

AN5105 - Rev 1

Principle

The STM32 touch sensing feature is based on charge transfer.

The surface charge transfer acquisition principle consists in charging a sensor capacitance (Cx) and in
transferring the accumulated charge into a sampling capacitor (Cs).

This sequence is repeated until the voltage across Cs reaches VIH.

The number of charge transfers required to reach the threshold is a direct representation of the size of the
electrode capacitance. When the sensor is touched, the sensor capacitance to the earth is increased. This mean
the C voltage reaches VIH with less count and the measurement value decreases. When this measurement goes

below a threshold, a detection is reported by the TSL. The schematic below do not take into account the parasitic
capacitor.

page 3/52

AN5105

Principle

Figure 1. Change transfer principle

V

DD

User finger

STM32

MCU

V

SS

Sampling
capacitor

Cs

Sensor capacitor

Cx

touchkey

sensor

eletrode

Human

body

coupling

to earth

Table 1. Change transfer principle documentation gives a list of documents containing information about the

change transfer principle.

Table 1. Change transfer principle documentation

Id

AN4299

AN4310

AN4312

AN4316 Tuning a STMTouch-based application Charge transfer periode tuning

OLT STM32L4 On Line Training Touch sensing controller (TSC)

Guidelines to improve conducted noise robustness on
STM32F0/F3/L0/L4 series touch sensing applications

Sampling capacitor selection guide for MCU based
touch sensing applications

Guidelines for designing touch sensing applications
with surface sensors

Title Chapters

Surface charge transfert acquisition principle overview

Charge transfert acquisition principle overview

Capacitive sensing technology in ST

AN5105 - Rev 1

page 4/52

3 Document reference

Figure 2. Main documentation tree shows the main documentation tree related to TSC and TSL.

AN5105

Document reference

Figure 2. Main documentation tree

Application Note

overview

(AN5105)

STM32 On-line

Training

TSC

Getting Started

with TSL

(UM1913)

Sensors

(AN4312)

ESD

(AN3960)

Tuning

(AN4316)

Conducted Noise

(AN4299)

Table 2. References documentation

Document name

UM1913 Developing applications on STM32Cube with STMTouch® touch sensing library

AN3960 ESD considerations for touch sensing applications

AN4299

AN4310 Sampling capacitor selection guide for MCU based touch sensing applications

AN4312 Guidelines for designing touch sensing applications with surface sensors

AN4316 Tuning a STMTouch-based application

Guidelines to improve conducted noise robustness on STM32F0/F3/L0/L4 series touch sensing
applications

Document title

Sampling
Capacitor
(AN4310)

AN5105 - Rev 1

page 5/52

STM32L4 touch sensing controller online presentation

4 STM32L4 touch sensing controller online presentation

An online training is available under our website www.st.com.

Insert the STM32L4 Online Training” string in the "Search" fuction and press enter.

To find it use the function "Search" and insert the strings “STM32L4 Online Training”. Figure 4. STM32L4 Touch

Sensing Controller online training shows the online page available .

Figure 3. STM32L4 online training

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Figure 4. STM32L4 Touch Sensing Controller online training

AN5105 - Rev 1

page 6/52

5 Main characteristics

5.1 Description

The following Figure 5. TSC characteristics shows all touch sensing controller (TSC) characteristics and their
correlation.

The TSC main characteristics are described in the following pages.

AN5105

Main characteristics

Figure 5. TSC characteristics

TSC

5.2

Signal

threshold

Charge
transfer

PCBSensorSensitivity

Guard ringShieldRotaryLinearKeys

Power
supply

False

detection

Noise

Noise

immunity

Conducted

Noise

Signal threshold

To tune the detection thresholds, it must determine the sensitivity of each touchkey. For each touchkey, can be
used few parameters to adjust these signal thresholds.

For debug purpose, it can get touchkey parameters using printf or STMStudio tool:

for (Index = 0;Index < NUMBER_OF_TOUCHKEYS;Index++)
{
printf("K%1d [%2d][%4d %3d %3d %4d] %d %d %d %d %d"
,Index
,MyTKeys[Index].p_Data->StateId
,MyTKeys[Index].p_ChD->Ref
,MyTKeys[Index].p_ChD->RefRest
,MyTKeys[Index].p_ChD->Delta
,MyTKeys[Index].p_ChD->Meas
,MyTKeys[Index].p_Param->ProxInTh
,MyTKeys[Index].p_Param->ProxOutTh
,MyTKeys[Index].p_Param->DetectInTh
,MyTKeys[Index].p_Param->DetectOutTh
,MyTKeys[Index].p_Param->CalibTh
);
}

Note: ProxInTh and ProxOutTh are defined for proximity detection feature only, when TSLPRM_USE_PROX = 1.

AN5105 - Rev 1

page 7/52

Figure 6. STMStudio outputs

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Signal threshold

• On software side:

– Relevant information are located in tsl_conf.h and tscl_user.c files.

– Threshold (xx_TH) can be adjust in tsl_conf_tsc.h file.:

See below an example:

#define TSLPRM_TKEY_DETECT_IN_TH (64)
#define TSLPRM_TKEY_DETECT_OUT_TH (60)
#define TSLPRM_TKEY_CALIB_TH (56)
#define TSLPRM_LINROT_DETECT_IN_TH (50)
#define TSLPRM_LINROT_DETECT_OUT_TH (40)

• The TSL api, tsl_user_SetThresholds, located in tsl_user.c allows to adjust each channel independently. See
below an example:

void tsl_user_SetThresholds(void)
{
/* USER CODE BEGIN Tsl_user_SetThresholds */
/* Example: Decrease the Detect thresholds for the TKEY 0*/
MyTKeys_Param[0].DetectInTh -= 10;
MyTKeys_Param[0].DetectOutTh -= 10;
/* USER CODE END Tsl_user_SetThresholds */
}

Table 3. Signal threshold usage documentation gives a list of documents containing information about the signal

threshold usage.

AN5105 - Rev 1

page 8/52

Id Title Chapters

UM1913

AN4316 Tuning a STMTouch-based application

Developing applications on STM32Cube with
STMTouch® touch sensing library

5.3 Charge transfer

The acquisition is based on the measurement of the sensor channel capacitance.

To ensure that the Cx capacitance is correctly charged, it is necessary to monitor the pin connected to the sensor.
On sensors and shield sides, it must observe a complete Charge/Discharge cycle.

AN5105

Charge transfer

Table 3. Signal threshold usage documentation

Debug with STMStudio

Monitoring STMTouch driver variables using
STMStudio

Tuning of the Thresholds

Touchkeys thersholds

Linear and Rotary touch sensors thresholds

Figure 7. Incomplete and complete charge transfert cycle

In this example , to complete the charge transfer cycles, the following parameter must be modified as below:

• INCREASE:

– htsc.Init.PulseGeneratorPrescaler

– htsc.Init.CTPulseHighLength

– htsc.Init.CTPulseLowLength

• DECREASE:

– Sysclk

Table 4. Charge transfer documentation gives a list of documents containing information about the charge

transfer.

Table 4. Charge transfer documentation

Id

AN4299

AN4316 Tuning a STMTouch-based application Charge transfer period tuning

Guidelines to improve conducted noise robustness on
STM32F0/F3/L0/L4 series touch sensing applications

Title Chapters

Active shield

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page 9/52

5.4 Sensitivity

Sensitivity is a key point in touch sensing applications. The sensitivity can be improved by:

• Reduce air gap

• Reduce panel thickness

• Choose dielectric with higher ε

• GND plane must not too close from shield and sensors

• Avoid metallic paint near shield and sensors

Table 5. Sensitivity documentation gives a list of documents containing information about the sensitivity.

Id Title Chapter

AN1913

AN4312

AN4316 Tuning a STMTouch-based application All chapter

R

Table 5. Sensitivity documentation

Developing applications on STM32Cube with
STMTouch® touch sensing library

Guidelines for designing touch sensing applications
with surface sensors

AN5105

Sensitivity

GPIO mode (table)

Air Gap:

• Reduce air gap

Changing the Panel material:

• Reduce Panel thickness

• Choose dielectric with higher ε

Metal chassis:

• GND not too closed from Shield and Sensors

• Avoid Metallic paint near Shield and Sensors

Mechanical construction and PCB to panel bonding.
Surface sensor design

R

Dielectric example

Table 6. Dielectric constants of common materials used in a panel construction

Polyethylene terephthalate (PET) 3.7

FR4 (fiberglass + epoxy 4.2

PMMA (Poly methyl methacrylate) 2.6 to 4

Material

Air 1.00059

Glass 4 to 10

Sapphire glass 9 to 11

Mica 4 to 8

Nylon 3

Plexiglass 3.4

Polyethylene 2.2

Polystyrene 2.56

Typical PSA 2.0 - 3.0 (approximately)

ε

R

AN5105 - Rev 1

page 10/52

5.5 Sensors

• It is recommended to use the same shape for all electrodes.

• The touchkeys can be customized by the drawing on the panel. TSL compensates capacitance differences.

• Acquisition time and processing parameters can be optimized when electrodes have similar capacitance.

Sensor size example

5.5.1 Key

• Key sensors are used in common application

• You can get deeper key information in following documents:

Table 7. Key documentation gives a list of documents containing information about the key.

AN5105

Sensors

Figure 8. Sensor size

Table 7. Key documentation

Id Title Chapters

UM1913

AN4312

Developing applications on STM32Cube with
STMTouch® touch sensing library

Guidelines for designing touch sensing applications
with surface sensors

Touchkey sensor

Touchkey sensor

AN5105 - Rev 1

page 11/52

5.5.2 Linear or slider

A linear is a set of contiguous capacitive electrodes. Figure 9. Interlaced linear touch sensor with 3 channels / 4

electrodes (half-ended electrodes design) shows a slider used on a discovery board.

Figure 9. Interlaced linear touch sensor with 3 channels / 4 electrodes (half-ended electrodes design)

AN5105

Sensors

Up to 60 mm

Full band width 3.6 mm

Tooth pitch

2.4 mm

Squared end

0.2~0.3 mm

Electrode/ground
gap 2 mm

Electrode gap 0.2~0.3 mm

Legend:

Via between layers

10% meshed ground plane

Copper electrode

Table 8. Linear touch sensor documentation gives a list of documents containing information about the linear

touch sensor.

Table 8. Linear touch sensor documentation

Id

UM1913

AN4312

Developing applications on STM32Cube with
STMTouch® touch sensing library

Guidelines for designing touch sensing
applications with surface sensors

Title Chapters

Linear and rotary touch sensors

Linear sensor

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page 12/52

5.5.3 Rotary or wheel

A rotary is a set of contiguous capacitive electrodes.

Figure 10. Interlaced patterned rotary sensor with 3 channels / 3 electrodes

Full band width 2.0 - 4.0 mm

Tooth pitch

2.0 - 4.0 mm

AN5105

Sensors

0.2 - 0.3 mm

0.2 - 0.3 mm

0.2 - 0.3 mm

2 mm

LEGEND:

Via between layers

10 % meshed ground plane

Copper electrode

Table 9. Rotary sensor documentation gives a list of documents containing information about the rotary sensor.

Table 9. Rotary sensor documentation

Id

UM1913

AN4312

Developing applications on STM32Cube with
STMTouch® touch sensing library

Guidelines for designing touch sensing applications
with surface sensors

Title Chapters

Linear and rotary touch sensors

Rotary sensor

AN5105 - Rev 1

page 13/52

5.5.4 Active shield or driven shield

Active shield or driven shield. (this name is used in some application notes) drives the shield plane with the same
signal as the electrode.

There are several advantages using Active Shield instead of a grounded shield:

• The parasitic capacitance between the electrode and the shield no longer needs to be charged.

• Protect the touch electrodes from a noise source.

• Increase system stability and performance when a moving metal part is close to the electrode.

Figure 11. Active shield principle

Rs

key

IO1

AN5105

Sensors

Touchkey

group X

Shield

group Y

IO2

IO3

IO4

IO1

IO2

IO3

IO4

Cs

Cs

key

shield

Rs

shield

Table 10. Active shield documentation gives a list of documents containing information about the active shield.

Table 10. Active shield documentation

AN5105 - Rev 1

Id

AN4299

AN4312

AN4316 Tuning a STMTouch-based application Shield adjustment

OLT STM32L4 Online Training Touch sensing controller (TSC)

Guidelines to improve conducted noise robustness
on STM32F0/F3/L0/L4 series touch sensing
applications

Guidelines for designing touch sensing
applications with surface sensors

Title Chapters

Active Shield

Driven shield

page 14/52

5.6 Layout and PCB

Rules to follow to improve TSC systems

5.6.1 Led rules

AN5105

Layout and PCB

Figure 12. Led layout example

Figure 13. Example of cases where a LED bypass capacitor is required

V

DD

V

DD

V

DD

Table 11. Led rules documentation gives a list of documents containing information about led rules.

Table 11. Led rules documentation

Id

AN4312

Guidelines for designing touch sensing applications
with surface sensors

Title Chapters

• LEDs and Sensors.

• Placing of LEDs close to sensor

AN5105 - Rev 1

page 15/52

5.6.2 Electrode not located on PCB

It is possible but it is not recommended, because when the electrode it isn't located on PCB, the sensitivity
decreases and additional extra parasitic capacitances are added.

Figure 14. Electrode not located on PCB example

AN5105

Layout and PCB

Front panel
(plexiglass or
other suitable

material)

Controller

PCB

Spring

Printed

electrode

Printed
electrode
(optional)

PCB pad

Spacer (cylinder

of hard foam or

other suitable

material)

Flex PCB

ACF/ACP

connection

Flex

connector

Table 12. Electrode documentation gives a list of documents containing information about the electrode .

Table 12. Electrode documentation

Id

AN4312

Guidelines for designing touch sensing applications

Title Chapters

with surface sensors

Using electrodes separated from the PCB

AN5105 - Rev 1

page 16/52

5.6.3 Ground, shield and sensors

Table 13 gives a list of documents containing information about the layout .

Id Title Chapters

AN4312

Figure 15 shows the ground plane and the signal tracks.

Guidelines for designing touch sensing applications
with surface sensors

AN5105

Layout and PCB

Table 13. Layout documentation

• PCB and Layout

• Ground considerations

• Rotary and linear sensor recommendations

Figure 15. Hatched ground and signal tracks

Must be avoided

Track is OK

Figure 16. Ground plane example

Tkey2

Tkey3

Hatched ground plane (optional)

Tkey1

Tkey4

Rx

Rx

Rx

Rx

Flood ground plane (mandatory)

GPIO1
GPIO2
GPIO3
GPIO4

C

S

AN5105 - Rev 1

page 17/52

Figure 17. Track routing

Figure 18. Track routing recommendation

At least 2 mm (4 - 5 mm is recommended)

AN5105

Layout and PCB

Ground plane or

ground track

Touchkey bank 1

At least

twice the

track width

As thin as

PCB

technology

allows

Any application track

(LED, power, Com.)

At least twice the

panel thickness

Touchkey bank 2

AN5105 - Rev 1

page 18/52

(W)

Figure 19. Shield

Top layer Bottom layer

Ground plane

Track width (W)

AN5105

Layout and PCB

~ 0.21

3-4 mm

Active shield

Sense plate

3 x W

AN5105 - Rev 1

page 19/52

5.6.4 FAQ

System keys points:

• Direct connection between earth and board ground is required to avoid conducted noise issues.

• Conductive painting on the front panel must be avoid.

• Robust mechanical assembly is required.

Layout keys points:

• GND plane is mandatory under MCU, sampling capacitors and up to serial resistors

• Hatched GND plane recommended for sensor traces from both sides of the PCB:

• Route the sensors and ground on the same layer while the components and other tracks are routed on the

Driven shield, or Active shield, is recommended.

• If there will be LEDs close to sensors, to indicate a touch event, they must be bypassed by a capacitor.

• External LDO regulator should be used to power the MCU only to provide a stable power supply voltage

• It is strongly recommended to dedicate pins to be used as touch sensors and do not share them with other

RS and CS keys points:

• PPS or NPO sampling capacitors are recommended. Possible X5R or X7R.

• Never use tantalium sampling capacitors.

• Serial ESD 10 K (down to 1 K) resistors are recommended to be placed as close as possible to the MCU

• No track crossing or via between these resistors and the MCU

• The value of sampling capacitor of active shield should be different than the value of the sampling capacitors

• The capacitance of active shield is higher (larger area) than CX of a single touch sensing channel. In order to

AN5105

Layout and PCB

– minimize parasitic capacitance

– mesh plane possible with 25% to 40% copper

other layers

typically 10 nF.

without any ripple, especially all the switching components like transistors, LEDs, in the application mustn't
be powered from the same voltage. This regulator should not be placed close to the sensors and their
tracks, but close to MCU.

features

used for acquisition.

achieve the same waveform on active shield and active touch sensing channel, the ratios CS/CX of active
shield and active touch sensing channel (touchkey). therefore, the CS of the active shield should also have

higher value (k x CS of touch sensing channel).

AN5105 - Rev 1

Sensor key points:

• Other traces must not cross the touch sensing traces or the whole touch sensing area

• The touch sensing traces should be as thin as technology allows and as short as possible.

– No longer than 10 cm

• The space between traces and GND plane should be ideally 5 mm

• TC pins are more robust against external interference than FT:

• Consider modification of PCB layout to allow connection of external VDD clamping diode to touch sensing
electrode traces.

– Use low‐capacitance diode like BAR18, BAS70 with Cmax = 2 pF.

– In case it is later needed, add pads and connection to the PCB without assembling components.

• Floating panes must never be placed close to the sensors.

page 20/52

5.7 Noise

Noise is a key point for touch sensing applications. Noise can come from Power supply.

5.7.1 Power supply

Main rules to follow:

• Place Buzzer and LED before LDO.

• Place LDO close to MCU.

Supply

input

Figure 20. Typical power supply schematic

LEDs

V

DD

V

1 μF 100 μF 100 μF 1 μF

IN

LDO

regulator

V

SS

V

OUT

(1)

AN5105

Noise

V

DD

V

DD

Touch sensing

device (MCU)

GPIO

V

SS

LED

10 nF

Table 14. Power supply documentation gives a list of documents containing information about the power supply.

Id

AN4312

Guidelines for designing touch sensing applications
with surface sensors

5.7.2 False detection

To avoid false detection TSL embed ECS, DXS and DTO algorithms.

Table 15. False detection documentation gives a list of documents containing information about the false

detection.

Id Title Chapters

UM1913

Developing applications on STM32Cube with
STMTouch® touch sensing library

Table 14. Power supply documentation

Title Chapters

Power supply

Table 15. False detection documentation

• Environment Change System (ECS)

– Power supply voltage, temperature and

air humidity

• Detection Exclusion System (DXS)

• Detection Time Out (DTO)

AN5105 - Rev 1

page 21/52

5.7.3 Noise immunity

Noise filtering can be done on hardware and software (TSL) sides.

Table 16. Noise immunity documentation gives a list of documents containing information about the noise

immunity.

Id Title Chapters

UM1913

AN4299

OLT STM32L4 Online Training Touch sensing controller (TSC)

Developing applications on STM32Cube with
STMTouch® touch sensing library

Guidelines to improve conducted noise robustness on
STM32F0/F3/L0/L4 series touch sensing applications

5.7.4 Conducted noise

• Touch sensing systems requires the conducted noise immunity.

• A key point is the signal to noise ratio (SNR).

• The test condition to be followed by the user is described in the standard IEC61000-4-6.

Table 17. Conducted noise documentation gives a list of documents containing information about the conducted

noise.

AN5105

Noise

Table 16. Noise immunity documentation

Noise filters

How to improve noise immunity

AN4299

Table 17. Conducted noise documentation

Id Title Chapters

Guidelines to improve conducted noise robustness
on STM32F0/F3/L0/L4 series touch sensing
applications

All chapters

AN5105 - Rev 1

page 22/52

6 Tuning

For tuning purpose dedicated application note are available.

Sensors

Table 18. Sensors documentation gives a list of documents containing information about the sensor.

Id Title Chapters

AN4312

ESD

Table 19. ESD documentation gives a list of documents containing information about the ESD

Table 18. Sensors documentation

Guidelines for designing touch sensing applications

with surface sensors

AN5105

Tuning

All chapters

Table 19. ESD documentation

Id Title Chapters

AN3960 ESD considerations for touch sensing applications All chapters

CN

Table 20. Conducted noise documentation gives a list of documents containing information about the conducted

noise.

Table 20. Conducted noise documentation

Id

AN4299

Guidelines to improve conducted noise robustness on

STM32F0/F3/L0/L4 series touch sensing applications

Title Chapters

All chapters

CS

Table 21. Sampling capacitor documentation gives a list of documents containing information about the sampling

capacitor.

Table 21. Sampling capacitor documentation

AN5105 - Rev 1

Id

AN4310

Title Chapters

Sampling capacitor selection guide for MCU based
touch sensing applications

All chapters

page 23/52

7 Getting started TSC with STM32CubeMX

7.1 Uses cases

How to set-up an TSC application based on TSL is esplained in the following two examples. These examples
describe the way to set-up TLS on STM32F072B-DISCO and STM32L0538-DISCO discovery boards.

This description can be used as example to set-up others TSC series such us L4, F3, L0, L1 and L4.

An STM32CubeMX new feature is available from version 4.24.0. This new feature can help to speed-up TSL,
TouchSensingLib, installation.

Figure 21. Main project panel

AN5105

AN5105 - Rev 1

page 24/52

7.2 Discovery board: STM32F072B-DISCO

The STM32F072 Discovery kit helps the user to discover the STM32F072, which has the full set of features
available in the STM32F0 Series, and to develop his applications easily. It includes everything required for
beginners and experienced users to get started quickly.

Based on the STM32F072RBT6, it includes an ST-LINK/V2 embedded debug tool interface, an ST MEMS
gyroscope, LEDs, push-buttons, linear touch sensor, RF EEPROM connector and a USB mini-B connector.

This discovery board provide a three channels linear (or slider) sensor. the main characteristics of these sensor
are:

• On-board ST-LINK/V2

• Supply through ST-Link USB

• External Supply: 3V and 5V

• JP2 (Idd) for current measurement

• Full-Speed USB with mini-B Connector

• Motion sensor, 3-axis digital output gyroscope (L3GD20)

• One Linear Touch Sensor or four Touch Keys

• Two Push-buttons: User and Reset

• Six LEDs: USB COM, 3.3 V Power, User (Orange/Green/Red/Blue)

• Extension header: (2 x 33) with 2.54 mm Pitch

• Discovery Board Formfactor

AN5105

Discovery board: STM32F072B-DISCO

7.2.1 STM32F072B-DISCO board selection

Start to select STM32F072B-DISCO board.

Figure 22. STM32F072B-DISCO board selection

To start Linear Touch Sensor channel acquisition at the same time, three groups are used. (See

Figure 23. STM32F072B-DISCO board schematics

AN5105 - Rev 1

page 25/52

Discovery board: STM32F072B-DISCO

Figure 23. STM32F072B-DISCO board schematics

AN5105

AN5105 - Rev 1

page 26/52

7.2.2 STM32F072B-DISCO TSC group and sensor activation

To activate the TSC group, sampling capacitors and sensor channels follows the below steps:

• activate TSC according schematics information.

• desactivate unrelevant peripheral like USB, SPI, NCF(L0), EPaper(L0), MFX(L0)

SWD peripheral must be set according to Figure 24

Figure 24. STM32F072B-DISCO pinout SWD

AN5105

Discovery board: STM32F072B-DISCO

TSC peripheral must be set according to Figure 25.

Figure 25. STM32F072B-DISCO pinout TSC

AN5105 - Rev 1

page 27/52

Figure 26 shows the results obtained.

Figure 26. STM32F072B-DISCO pinout overview

AN5105

Discovery board: STM32F072B-DISCO

7.2.3 STM32F072B-DISCO clock tree

It uses the default clock tree setting.

Figure 27. STM32F072B-DISCO clock configuration

AN5105 - Rev 1

page 28/52

7.2.4 STM32F072B-DISCO touchsensing library

To activate the TLS usage, switch on TOUCHSENSING box configuration.

Figure 28. TOUCHSENSING box configuration

AN5105

Discovery board: STM32F072B-DISCO

Select three channels Linear slider and assign dedicated Gx_IOy (see previous chapter or schematics for details).

• For training purpose, we can used three channels Linear slider as three keys sensors.

• Select three keys and assign dedicated Gx_IOy (see previous chapter or schematics for details).

Figure 29 to Figure 33 show these steps.

Figure 29. STM32F072B-DISCO sensor selection

AN5105 - Rev 1

page 29/52

Discovery board: STM32F072B-DISCO

Figure 30. STM32F072B-DISCO sensor selection step2

AN5105

Figure 31. STM32F072B-DISCO sensor selection step3

AN5105 - Rev 1

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Discovery board: STM32F072B-DISCO

Figure 32. STM32F072B-DISCO sensor selection step4

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Figure 33. STM32F072B-DISCO sensor selection step5

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7.2.5 STM32F072B-DISCO software project generation

Now, it is possible to generate the complete software project based on TSC HAL and TSL.

Figure 34 to Figure 37 show all these steps.

Figure 34. STM32F072B-DISCO software generation step1

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Figure 35. STM32F072B-DISCO software generation step2

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Discovery board: STM32F072B-DISCO

Figure 36. STM32F072B-DISCO software generation step3

Figure 37. STM32F072B-DISCO IDE workspace

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7.2.6 STM32F072B-DISCO software basic algorythm

The user needs now to write the main application loop.

Example to show keys usage instead of slider usage.

• Open your IDE and in main.c file add the following lines:

/* USER CODE BEGIN 3 */
extern TSL_LinRot_T MyLinRots[];
static uint32_t cnt=0;
tsl_user_status_t status = TSL_USER_STATUS_BUSY;
status = tsl_user_Exec();
if(TSL_USER_STATUS_BUSY == status)
{
// Nothing to do
if(cnt++%50==0){
HAL_GPIO_TogglePin(LD3_GPIO_Port, LD3_Pin);
}
HAL_Delay(1);
}
else
{
if(MyLinRots[0].p_Data->StateId == TSL_STATEID_DETECT)
{
//TSLPRM_LINROT_RESOLUTION
if(MyLinRots[0].p_Data->Position >= 5 && MyLinRots[0].p_Data->Position < 50)
{
HAL_GPIO_WritePin(LD4_GPIO_Port, LD4_Pin, GPIO_PIN_SET);
HAL_GPIO_WritePin(LD6_GPIO_Port, LD6_Pin, GPIO_PIN_RESET);
HAL_GPIO_WritePin(LD5_GPIO_Port, LD5_Pin, GPIO_PIN_RESET);
}
if(MyLinRots[0].p_Data->Position >= 50 && MyLinRots[0].p_Data->Position < 80)
{
HAL_GPIO_WritePin(LD6_GPIO_Port, LD6_Pin, GPIO_PIN_SET);
HAL_GPIO_WritePin(LD4_GPIO_Port, LD4_Pin, GPIO_PIN_RESET);
HAL_GPIO_WritePin(LD5_GPIO_Port, LD5_Pin, GPIO_PIN_RESET);
}
if(MyLinRots[0].p_Data->Position >= 80 && MyLinRots[0].p_Data->Position < 120)
{
HAL_GPIO_WritePin(LD5_GPIO_Port, LD5_Pin, GPIO_PIN_SET);
HAL_GPIO_WritePin(LD4_GPIO_Port, LD4_Pin, GPIO_PIN_RESET);
HAL_GPIO_WritePin(LD6_GPIO_Port, LD6_Pin, GPIO_PIN_RESET);
}
}
else //if(MyLinRots[0].p_Data->StateId == TSL_STATEID_RELEASE)
{
HAL_GPIO_WritePin(LD4_GPIO_Port, LD4_Pin, GPIO_PIN_RESET);
HAL_GPIO_WritePin(LD5_GPIO_Port, LD5_Pin, GPIO_PIN_RESET);
HAL_GPIO_WritePin(LD6_GPIO_Port, LD6_Pin, GPIO_PIN_RESET);
}
}
}
/* USER CODE END 3 */

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Take care of ST-Link setup, see Figure 38. STM32F072B-DISCO setup.

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Figure 38. STM32F072B-DISCO setup

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Discovery board: STM32F072B-DISCO

Now the system is functional and ready to be used. Led will blink according finger position on slider.

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7.3 Discovery board: STM32L0538-DISCO

The STM32L053 discovery kit helps you to discover the ultra-low-power microcontrollers of the STM32L0 series.
It offers everything required for beginners and experienced users to get started quickly and develop applications
easily.

Based on an STM32L053C8T6, it includes an ST-LINK/V2-1 embedded debug tool interface, linear touch sensor,
IDD current measurement, 2.04” E-paper display, NFC connector for PLUG-CR95HF-B board, LEDs, pushbuttons
and a USB Mini-B connector.

This discovery board provide a three channels linear (or slider) sensor. Their main characteristics are:

• On-board ST-LINK/V2-1

• Supply through ST-Link USB

• External Supply : 3V and 5V

• JP4 (Idd) for current measurement

• Full-Speed USB with mini-B Connector

• E-paper 2.04" display (172 x 72)

• One Linear Touch Sensor or four Touch Keys

• Two Push-buttons: User and Reset

• Four LEDs: USB COM, 3.3 V Power, user (Green/Red)

• Extension header: (2 x 25) with 2.54 mm Pitch

• Discovery Board Formfactor

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Discovery board: STM32L0538-DISCO

7.3.1 STM32L0538-DISCO board selection

Start to select STM32L0538-DISCO board.

Figure 39. STM32L0538-DISCO board selection

To start linear touch sensor channel acquisition at the same time, three groups are used.

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Discovery board: STM32L0538-DISCO

Figure 40. STM32L0538-DISCO board schematics

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7.3.2 STM32L0538-DISCO TSC group and sensor activation

To activate the TSC group, sampling capacitors and sensor channels follows the below steps:

• Activate TSC according schematics information.

• You can deactivate unrelevant peripheral like USB, SPI, NCF(L0), EPaper(L0), MFX(L0)

SWD peripheral must be set according to Figure 41.

Figure 41. Pinout SWD

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Discovery board: STM32L0538-DISCO

TSC peripheral must be set according to Figure 42.

Figure 42. Pinout TSC

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Figure 43 shows the results obtained.

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Discovery board: STM32L0538-DISCO

Figure 43. Pinout overview

7.3.3 STM32L0538-DISCO clock tree

It uses the default clock tree setting.

Figure 44. Clock configuration

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7.3.4 STM32L0538-DISCO touchsensing library

To activate the TLS usage, switch on TOUCHSENSING box configuration.

Figure 45. TOUCHSENSING box configuration

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Discovery board: STM32L0538-DISCO

Select 3 channels Linear slider and assign dedicated Gx_IOy (see previous chapter or schematics for details).

For training purpose, the user can:

• use three channels linear slider as three keys sensors

• Select three keys and assign dedicated Gx_IOy (see previous chapter or schematics for tedails).

Follow Figure 46 to Figure 50 to set sensors.

Figure 46. STM32L0538-DISCO sensor selection step1

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Discovery board: STM32L0538-DISCO

Figure 47. STM32L0538-DISCO sensor selection step2

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Figure 48. STM32L0538-DISCO sensor selection step3

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Discovery board: STM32L0538-DISCO

Figure 49. STM32L0538-DISCO sensor selection step4

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Figure 50. STM32L0538-DISCO sensor selection step5

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7.3.5 STM32L0538-DISCO software project generation

Now, it is possible to generate the complete software project based on TSC HAL and TSL.

See details in Figure 51 to Figure 55.

Figure 51. STM32L0538-DISCO software generation step1

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Figure 52. STM32L0538-DISCO software generation step2

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Discovery board: STM32L0538-DISCO

Figure 53. STM32L0538-DISCO complete project overview

Figure 54. STM32L0538-DISCO IDE workspace

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Figure 55. SWD settings

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7.3.6 STM32L0538-DISCO software basic algorithm

Below is showed an example to show keys usage instead of slider usage.

• Open your IDE and in main.c file add the following lines:

/* USER CODE BEGIN 3 */
extern TSL_TouchKey_T MyTKeys[];
static uint32_t cnt=0;
tsl_user_status_t status = TSL_USER_STATUS_BUSY;

status = tsl_user_Exec();
if(TSL_USER_STATUS_BUSY == status)
{
// Nothing to do
if(cnt++%50==0){
}
HAL_Delay(1);
}
else
{
HAL_GPIO_WritePin(LD_R_GPIO_Port, LD_R_Pin, GPIO_PIN_RESET); //00
HAL_GPIO_WritePin(LD_G_GPIO_Port, LD_G_Pin, GPIO_PIN_RESET);
if(MyTKeys[0].p_Data->StateId == TSL_STATEID_DETECT)
{
HAL_GPIO_WritePin(LD_R_GPIO_Port, LD_R_Pin, GPIO_PIN_SET); //11
HAL_GPIO_WritePin(LD_G_GPIO_Port, LD_G_Pin, GPIO_PIN_SET);
}
if(MyTKeys[1].p_Data->StateId == TSL_STATEID_DETECT)
{
HAL_GPIO_WritePin(LD_R_GPIO_Port, LD_R_Pin, GPIO_PIN_SET); //01
HAL_GPIO_WritePin(LD_G_GPIO_Port, LD_G_Pin, GPIO_PIN_RESET);
}
if(MyTKeys[2].p_Data->StateId == TSL_STATEID_DETECT)
{
HAL_GPIO_WritePin(LD_R_GPIO_Port, LD_R_Pin, GPIO_PIN_RESET);//01
HAL_GPIO_WritePin(LD_G_GPIO_Port, LD_G_Pin, GPIO_PIN_SET);
}
}
}
/* USER CODE BEGIN 3 */

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Now the system is functional and ready to be used.

The Led is blink according to the position of the on slider.

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Revision history

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Table 22. Document revision history

Date Version Changes

19-Sep-2018 1 Initial release.

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Contents

Contents

1 General information ...............................................................2

2 Terminology and principle .........................................................3

2.1 Terminology ...................................................................3

2.2 Principle ......................................................................3

3 Document reference ...............................................................5

4 STM32L4 touch sensing controller online presentation .............................6

5 Main characteristics ...............................................................7

5.1 Description ....................................................................7

5.2 Signal threshold................................................................7

5.3 Charge transfer ................................................................9

5.4 Sensitivity ....................................................................10

5.5 Sensor ......................................................................10

5.5.1 Key ..................................................................11

5.5.2 Linear or slider .........................................................12

5.5.3 Rotary or wheel.........................................................13

5.5.4 Active shield or driven shield...............................................14

5.6 Layout and PCB ..............................................................15

5.6.1 Led rules ..............................................................15

5.6.2 Electrode not located on PCB ..............................................16

5.6.3 Ground, shield and sensors ...............................................17

5.6.4 FAQ .................................................................20

5.7 Noise........................................................................21

5.7.1 Power supply ..........................................................21

5.7.2 False detection .........................................................21

5.7.3 Noise immunity .........................................................22

5.7.4 Conducted noise ........................................................22

6 Tuning............................................................................23

7 Getting started TSC with STM32CubeMX ..........................................24

7.1 Uses cases ..................................................................24

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Contents

7.2 Discovery board: STM32F072B-DISCO...........................................25

7.2.1 STM32F072B-DISCO board selection .......................................25

7.2.2 TSC group and sensor activation ...........................................27

7.2.3 STM32F072B-DISCO clock tree ............................................28

7.2.4 STM32F072B-DISCO touchsensing library ....................................29

7.2.5 STM32F072B-DISCO software project generation ..............................32

7.2.6 Software basic algorythm .................................................34

7.3 Discovery board: STM32L0538-DISCO ...........................................36

7.3.1 STM32L0538-DISCO board selection ........................................36

7.3.2 STM32L0538-DISCO TSC group and sensor activation ..........................38

7.3.3 STM32L0538-DISCO clock tree ............................................39

7.3.4 STM32L0538-DISCO touchsensing library ....................................40

7.3.5 STM32L0538-DISCO software project generation ..............................43

7.3.6 STM32L0538-DISCO software basic algorythm ................................45

Revision history .......................................................................46

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List of tables

List of tables

Table 1. Change transfer principle documentation ...................................................4

Table 2. References documentation ............................................................. 5

Table 3. Signal threshold usage documentation .....................................................9

Table 4. Charge transfer documentation ..........................................................9

Table 5. Sensitivity documentation ............................................................. 10

Table 6. Dielectric constants of common materials used in a panel construction ..............................10

Table 7. Key documentation ................................................................. 11

Table 8. Linear touch sensor documentation ...................................................... 12

Table 9. Rotary sensor documentation .......................................................... 13

Table 10. Active shield documentation ...........................................................14

Table 11. Led rules documentation .............................................................. 15

Table 12. Electrode documentation ............................................................. 16

Table 13. Layout documentation ............................................................... 17

Table 14. Power supply documentation........................................................... 21

Table 15. False detection documentation ......................................................... 21

Table 16. Noise immunity documentation ......................................................... 22

Table 17. Conducted noise documentation ........................................................22

Table 18. Sensors documentation .............................................................. 23

Table 19. ESD documentation .................................................................23

Table 20. Conducted noise documentation ........................................................23

Table 21. Sampling capacitor documentation ....................................................... 23

Table 22. Document revision history .............................................................46

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List of figures

List of figures

Figure 1. Change transfer principle .............................................................4

Figure 2. Main documentation tree ............................................................. 5

Figure 3. STM32L4 online training .............................................................6

Figure 4. STM32L4 Touch Sensing Controller online training ...........................................6

Figure 5. TSC characteristics ................................................................. 7

Figure 6. STMStudio outputs .................................................................8

Figure 7. Incomplete and complete charge transfert cycle .............................................9

Figure 8. Sensor size ..................................................................... 11

Figure 9. Interlaced linear touch sensor with 3 channels / 4 electrodes (half-ended electrodes design) ............. 12

Figure 10. Interlaced patterned rotary sensor with 3 channels / 3 electrodes ................................ 13

Figure 11. Active shield principle ..............................................................14

Figure 12. Led layout example................................................................ 15

Figure 13. Example of cases where a LED bypass capacitor is required ................................... 15

Figure 14. Electrode not located on PCB example .................................................. 16

Figure 15. Hatched ground and signal tracks ......................................................17

Figure 16. Ground plane example ............................................................. 17

Figure 17. Track routing .................................................................... 18

Figure 18. Track routing recommendation ........................................................ 18

Figure 19. Shield ......................................................................... 19

Figure 20. Typical power supply schematic ....................................................... 21

Figure 21. Main project panel.................................................................24

Figure 22. STM32F072B-DISCO board selection ...................................................25

Figure 23. STM32F072B-DISCO board schematics .................................................26

Figure 24. STM32F072B-DISCO pinout SWD ..................................................... 27

Figure 25. STM32F072B-DISCO pinout TSC...................................................... 27

Figure 26. STM32F072B-DISCO pinout overview................................................... 28

Figure 27. STM32F072B-DISCO clock configuration................................................. 28

Figure 28. TOUCHSENSING box configuration .................................................... 29

Figure 29. STM32F072B-DISCO sensor selection .................................................. 29

Figure 30. STM32F072B-DISCO sensor selection step2 ..............................................30

Figure 31. STM32F072B-DISCO sensor selection step3 ..............................................30

Figure 32. STM32F072B-DISCO sensor selection step4 ..............................................31

Figure 33. STM32F072B-DISCO sensor selection step5 ..............................................31

Figure 34. STM32F072B-DISCO software generation step1 ........................................... 32

Figure 35. STM32F072B-DISCO software generation step2 ........................................... 32

Figure 36. STM32F072B-DISCO software generation step3 ........................................... 33

Figure 37. STM32F072B-DISCO IDE workspace ................................................... 33

Figure 38. STM32F072B-DISCO setup .......................................................... 35

Figure 39. STM32L0538-DISCO board selection ................................................... 36

Figure 40. STM32L0538-DISCO board schematics..................................................37

Figure 41. Pinout SWD .....................................................................38

Figure 42. Pinout TSC ..................................................................... 38

Figure 43. Pinout overview .................................................................. 39

Figure 44. Clock configuration ................................................................ 39

Figure 45. TOUCHSENSING box configuration .................................................... 40

Figure 46. STM32L0538-DISCO sensor selection step1 .............................................. 40

Figure 47. STM32L0538-DISCO sensor selection step2 .............................................. 41

Figure 48. STM32L0538-DISCO sensor selection step3 .............................................. 41

Figure 49. STM32L0538-DISCO sensor selection step4 .............................................. 42

Figure 50. STM32L0538-DISCO sensor selection step5 .............................................. 42

Figure 51. STM32L0538-DISCO software generation step1............................................ 43

Figure 52. STM32L0538-DISCO software generation step2............................................ 43

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List of figures

Figure 53. STM32L0538-DISCO complete project overview............................................ 44

Figure 54. STM32L0538-DISCO IDE workspace ................................................... 44

Figure 55. SWD settings .................................................................... 44

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IMPORTANT NOTICE – PLEASE READ CAREFULLY

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Information in this document supersedes and replaces information previously supplied in any prior versions of this document.

© 2018 STMicroelectronics – All rights reserved

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