PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide

Figure 4. Parasitic capacitance shows how a GPIO pin is connected to a sensor pad by traces and vias for self-capacitance sensing. Typically, a ground (GND) hatch surrounds the sensor pad to isolate it from other sensors and traces. Although Figure 4. Parasitic capacitance shows some field lines around the sensor pad, the actual electric field distribution is very complex.

When a finger is present on the overlay, the conductive nature and large mass of the human body forms a grounded, conductive plane parallel to the sensor pad, as Figure 5. Finger capacitance shows.

This arrangement forms a parallel plate capacitor. The capacitance between the sensor pad and the finger is shown in Equation 1.

Where:

ε₀ = Free space permittivity

ε_r = Relative permittivity of overlay

A = Area of finger and sensor pad overlap

d = Thickness of the overlay

C_F = Finger capacitance.

C_P and C_F are parallel to each other because both represent the capacitance between the sensor pin and ground. Therefore, the total capacitance C_S of the sensor, when the finger is present on the sensor, is the sum of C_P and C_F.

In the absence of touch, C_S is equal to C_P.

PSoC™ converts the capacitance CS into equivalent digital counts called raw counts. Because a finger touch increases the total capacitance of the sensor pin, an increase in the raw counts indicates a finger touch. Refer to the CSD specification in Device datasheet/Component datasheet/middleware document document to learn about the supported CP range for a given device with which the recommended SNR can be achieved.

Figure 8. Mutual-capacitance sensing shows the button sensor layout for mutual-capacitance sensing. Mutual-capacitance sensing measures the capacitance between two electrodes, transmit (Tx) electrode and receive (Rx) electrode.

In a mutual-capacitance sensing system, a digital voltage signal switching between VDDIO ² or VDDD³ (if VDDIO is not supported by the device) and GND is applied to the Tx pin and the amount of charge received on the Rx pin is measured. The amount of charge received on the Rx electrode is directly proportional to the mutual-capacitance (C_M) between the two electrodes.

When a finger is placed between the Tx and Rx electrodes, the mutual-capacitance decreases to C¹ _M , as shown in Figure 9. Mutual-capacitance with finger touch. Because of the reduction in the mutual-capacitance, the charge received on the Rx electrode also decreases. The CAPSENSE™ system measures the amount of charge received on the Rx electrode to detect a touch/no touch condition.

Figure 11. Simplified diagram of CSD method shows a simplified block diagram of the CSD method.

In CSD, each GPIO has a switched-capacitance circuit that converts C_s into an equivalent current. An analog MUX (AMUX) selects one of the sensor currents and feeds it into the current to digital converter. The current to digital converter is similar to a delta sigma ADC. The output count of the current to digital converter, known as raw count, is a digital value that is proportional to the self-capacitance between the electrodes.

Where,

G_CSD = Capacitance to digital conversion gain of CSD

C_S = Self-capacitance of the electrode

Figure 14. Raw count versus time illustrates a plot of raw count over time. When a finger touches the sensor, the C_S increases from C_P to C_P + C_F, and the raw count increases. By comparing the change in raw count to a predetermined threshold, logic in firmware decides whether the sensor is active (finger is present).

Figure 12. Simplified diagram of CAPSENSE™ crosspoint (CSX) method shows the simplified block diagram of the CSX method.

With CSX, a voltage on the Tx electrode couples charge on to the RX electrode. This charge is proportional to the mutual capacitance between the Tx and Rx electrodes. An analog MUX then selects one of the Rx electrodes and feeds it into the current to digital converter.

The output count of the current to digital converter, , is a digital value that is proportional to the mutual-capacitance between the Rx and Tx electrodes as shown in Figure 13. Raw count and sensor capacitance relationship in CSX.

Where,

G_{C SX} = Capacitance to digital conversion gain of mutual capacitance method

C_M = Mutual-capacitance between two electrodes

Figure 14. Raw count versus time illustrates a plot of raw count over time. When a finger touches the sensor, C_M decreases from C_M to C¹ _M (see Figure 9. Mutual-capacitance with finger touch) hence the counter output decreases. The firmware normalizes the raw count such that the raw counts go high when C_M decreases. This maintains the same visual representation of raw count between CSD and CSX methods. By comparing the change in raw count to a predetermined threshold, logic in firmware decides whether the sensor is active (finger is present). The normalized inverted raw count is computed using Figure 58. Formula to determine rawcount_Component.

For an in-depth discussion of the PSoC™ 4 and PSoC™ 6 CAPSENSE™ CSD and CSX blocks, see chapter PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™.

CAPSENSE™ buttons replace mechanical buttons in a wide variety of applications such as home appliances, medical devices, white goods, lighting controls, and many other products. It is the simplest type of CAPSENSE™ widget, consisting of a single sensor. A CAPSENSE™ button gives one of two possible output states: active (finger is present) or inactive (finger is not present). These two states are also called ON and OFF states, respectively.

For the self-capacitance (CSD) sensing method, a simple CAPSENSE™ button consists of a circular copper pad connected to a PSoC™ GPIO with a PCB trace. The CAPSENSE™ button is surrounded by grounded copper hatch that isolates it from other buttons and traces. A circular gap separates the button pad and the ground hatch. Each button requires one PSoC™ GPIO. These buttons can be constructed using any conductive material on a non-conductive substrate; for example, indium tin oxide on a glass substrate, or silver ink on a non-conductive film. Even metallic springs can be used as button sensors; see Sensor construction for more details.

For the mutual-capacitance (CSX) sensing method, each button requires one GPIO pin configured as Tx electrode and one GPIO pin configured as Rx electrode. The Tx can be shared across multiple buttons, as shown in Figure 18. Simple CAPSENSE™ buttons for mutual-capacitance sensing method.

If the application requires many buttons (for example in a calculator keypad or a QWERTY keyboard), you can arrange the CAPSENSE™ buttons in a matrix, as Figure 19. Matrix buttons based on CSD shows. This allows a design to have multiple buttons per GPIO. For example, the 16-button design in Figure 19. Matrix buttons based on CSD requires only eight GPIOs.

A matrix button design has two groups of capacitive sensors: row sensors and column sensors. The matrix button architecture can be used for both self-capacitance (CSD) and mutual-capacitance (CSX) methods.

In CSD mode, each button consists of a row sensor and a column sensor, as Figure 19. Matrix buttons based on CSD shows. When a button is touched, both row and column sensors of that button become active. The CSD-based matrix button should be used only if the user is expected to touch one button at a time. If the user touches more than one diagonally opposite buttons, the finger location cannot be resolved as Figure 20. Ghost effect in matrix button based on CSD shows. This effect is called as ghost effect, which is considered an invalid condition.

Mutual-capacitance is the recommended sensing method for matrix buttons because this method is not affected from the ghost touch phenomena and provides better SNR for high C_p sensors. This is because it senses mutual-capacitance formed at each intersection rather than sensing rows and columns as shown in Figure 21. Matrix button based on CSX. Applications that require simultaneous sensing of multiple buttons, such as a keyboard with Shift, Ctrl, and Alt keys can use CSX sensing method or you should design the Shift, Ctrl, and Alt keys as individual CSD buttons.

Sliders are used when the required input is in the form of a gradual increment or decrement. Examples include lighting control (dimmer), volume control, graphic equalizer, and speed control. Currently, the CAPSENSE™ Component in PSoC™ Creator and ModusToolbox™ supports only self-capacitance-based sliders. Mutual capacitance-based sliders will be supported in future version of component.

A slider consists of a one-dimensional array of capacitive sensors called segments, which are placed adjacent to one another. Touching one segment also results in partial activation of adjacent segments. The firmware processes the raw counts from the touched segment and the nearby segments to calculate the position of the geometric center of the finger touch, which is known as the centroid position.

The actual resolution of the calculated centroid position is much higher than the number of segments in a slider. For example, a slider with five segments can resolve at least 100 physical finger positions. This high resolution gives smooth transitions of the centroid position as the finger glides across a slider.

In a linear slider, the segments are arranged inline, as Figure 22. Linear slider shows. Each slider segment connects to a PSoC™ GPIO. A zigzag pattern (double chevron) is recommended for slider segments. This layout ensures that when a segment is touched, the adjacent segments are also partially touched, which aids estimation of the centroid position.

Radial sliders are similar to linear sliders except that radial sliders are continuous. Figure 23. Radial slider shows a typical radial slider.

A touchpad (also known as trackpad) has two linear sliders arranged in an X and Y pattern, enabling it to locate a finger’s position in both X and Y dimensions. Figure 24. Touchpad sensor arrangement shows a typical arrangement of a touchpad sensor. Similar to the matrix buttons, touchpads can also be sensed using either CSD or CSX sensing method.

CSD-based touchpads suffer from ghost touches, so it supports only single-point touch applications.

CSX touchpads can support multi-point touch applications, but these may need more scanning time compared to CSD touchpad because this method scans each intersection rather than rows and columns.

Proximity sensors detect the presence of a hand in the three-dimensional space around the sensor. However, the actual output of the proximity sensor is an ON/OFF state similar to a CAPSENSE™ button. Proximity sensing can detect a hand at a distance of several centimeters to tens of centimeters depending on the sensor construction. Self capacitance is the recommended method of sensing for a proximity application.

Proximity sensing requires electric fields that are projected to much larger distances than buttons and sliders. This demands a large sensor area. However, a large sensor area also results in a large parasitic capacitance C_P, and detection becomes more difficult. This requires a sensor with high electric field strength at large distances while also having a small area. Figure 25. Proximity sensor shows a proximity sensor using a trace with a thickness of 2-3 mm surrounding the other sensors.

You can also implement a proximity sensor by ganging other sensors together. This is accomplished by combining multiple sensor pads into one large sensor using firmware. The disadvantage of this method is high parasitic capacitance. See the Component datasheet/middleware document for details on maximum parasitic capacitance supported by a given device.

See AN92239 proximity sensing with CAPSENSE™ and the proximity sensing section in Getting started with CAPSENSE™ design guide to learn more about proximity sensors.

In certain applications, the CAPSENSE™ system has to work in the presence of a variety of liquids such as soap water, sea water, and mineral water. In such applications, it is always recommended to tune the CAPSENSE™ parameters for sensors by considering the worst-case signal due to liquid droplets. To simulate the worst-case conditions, it is recommended that you test the liquid-tolerance performance of the sensors with salty water by dissolving 40 grams of cooking salt (NaCl) in one liter of water. Tests were done using soapy water; the results show that the effect of soapy water is similar to the effect of salty water. Therefore, if the tuning is done to reject salty water, the CAPSENSE™ system will work even in the presence of soapy water.

In applications such as induction cooktops, there are chances of hot water spilling on to the CAPSENSE™ touch surface. To determine the impact of the temperature of a liquid droplet on CAPSENSE™ performance, droplets of water at different temperatures were poured on a sensor and the corresponding change in raw counts was monitored. Experiment shows that the effect of hot liquid droplets is same as that of the liquid at room temperature as Figure 38. Raw count variation versus water temperature shows. This is because the hot liquid droplet cools down immediately to room temperature when it falls on the touch surface. If hot water continuously falls on the sensor and the temperature of the overlay rises because of the hot water, the increase in raw count due to the increase in temperature is compensated by the Baseline update algorithm, thereby preventing any false triggering of the sensors.

In the CAPSENSE™ CSD system, the GPIO cells are configured as switched-capacitance circuits that convert sensor capacitances into equivalent currents. Figure 40. GPIO cell structure shows a simplified diagram of the GPIO cell structure.

PSoC™ 4 and PSoC™ 6 devices consist of two AMUX buses: AMUXBUS A is used for CSD sensing and AMUXBUS B is used for CAPSENSE™ CSD shielding . The GPIO switched-capacitance circuit has two possible configurations: source current to AMUXBUS A or sink current from AMUXBUS A

In the IDAC Sourcing mode, the GPIO cell sinks current from the AMUXBUS A through a switched capacitor circuit as Figure 41. GPIO cell sinking current from AMUXBUS A shows.

Two non-overlapping, out-of-phase clocks of frequency F_SW control the switches SW₁ and SW₃ as Figure 42. SW₁ and SW₃ switch in non-overlapping manner shows. The continuous switching of SW₁ and SW₃ forms an equivalent resistance R_S, as Figure 41. GPIO cell sinking current from AMUXBUS A shows.

If the switches operate at a sufficiently low frequency F_SW, such that time T_SW/2 is sufficient to fully charge the sensor to V_REF and fully discharge it to ground, as Figure 42. SW₁ and SW₃ switch in non-overlapping manner shows, the value of the equivalent resistance R_S is given by Figure 43. Sensor equivalent resistance.

Where,

C_S = Sensor capacitance

F_SW = Frequency of the sense clock

The sigma-delta converter maintains the voltage of AMUXBUS A at a constant V_REF (this process is explained in Sigma-delta converter. Figure 44. Voltage across sensor capacitance shows the resulting voltage waveform across C_S.

Figure 45. Average current sinked from AMUXBUS A to GPIO through CAPSENSE™ sensor (ICS) gives the value of average current taken from AMUXBUS A.

In the IDAC sinking mode, the GPIO cell sources current to the AMUXBUS A through a switched capacitor circuit as Figure 46. GPIO cell sourcing current to AMUXBUS A shows. Figure 47. Voltage across sensor capacitance shows the voltage waveform across the sensor capacitance.

Because this mode charges the AMUXBUS A directly through V_DDD, it is more susceptible to power supply noise compared to the IDAC sourcing mode. Hence, it is recommended to use this mode with an LDO or a very stable and quiet V_DDD.

Figure 48. Average current sourced to AMUXBUS A from GPIO through CAPSENSE™ sensor (ICS) provides the value of average current supplied to AMUXBUS A.

The CAPSENSE™ clock generator block generates the sense clock F_SW, and the modulation clock F_MOD, from the high-frequency system resource clock (HFCLK) or peripheral clock (PERI) depending on the PSoC™ device family as shown in Figure 39. CAPSENSE™ CSD sensing.

The sigma-delta converter converts the input current to a corresponding digital count. It consists of a sigma-delta converter and two current sourcing/sinking digital-to-analog converters (IDACs) called modulation IDAC and compensation IDAC as Figure 39. CAPSENSE™ CSD sensing shows.

The sigma-delta converter uses an external integrating capacitor, called modulator capacitor C_MOD, as Figure 39. CAPSENSE™ CSD sensing shows. Sigma-delta converter controls the modulation IDAC current by switching it ON or OFF corresponding to the small voltage variations across C_MOD to maintain the C_MOD voltage at V_REF. The recommended value of C_MOD is listed in .

The sigma-delta converter can operate in either IDAC sourcing mode or IDAC sinking mode.

• IDAC sourcing mode: In this mode, the GPIO cell capacitance to charge converter sinks current from C_MOD through AMUXBUS A, and the IDACs then source current to AMUXBUS A to balance its voltage
• IDAC sinking mode: In this mode,the GPIO cell capacitance to charge converter sources current from C_MOD to AMUXBUS A and the IDACs sink current through AMUXBUS A to balance its voltage

In both the above-mentioned modes, the sigma delta converter can operate in either single IDAC mode or dual IDAC mode:

• In the single IDAC mode, the modulation IDAC is controlled by the sigma-delta converter; the compensation IDAC is always OFF
• In the dual IDAC mode, the modulation IDAC is controlled by the sigma-delta converter; the compensation IDAC is always ON

In the single IDAC mode, if ‘N’ is the resolution of the sigma-delta converter and I_MOD is the value of the modulation IDAC current, the approximate value of raw count in the IDAC Sourcing mode is given by Equation 10.

Similarly, the approximate value of raw count in the IDAC sinking mode is given by Equation 11.

In both cases, the raw count is proportional to sensor capacitance C_S. The raw count is then processed by the CAPSENSE™ CSD Component firmware to detect touches. The hardware parameters such as I_MOD, I_COMP, and F_SW, and the software parameters, should be tuned to optimum values for reliable touch detection. For an in-depth discussion of the tuning, see CAPSENSE™ performance tuning.

In the dual IDAC mode, the compensation IDAC is always ON. If I_COMP is the compensation IDAC current, the equation for the raw count in the IDAC sourcing mode is given by Equation 12.

Raw count in the IDAC sinking mode is given by Equation 13.

The relation between the parameters shown in the above equation to the CAPSENSE™ Component parameters is listed in .

The sigma delta converter scans one sensor at a time. An analog multiplexer selects one of the GPIO cells and connects it to the input of the sigma delta converter, as Figure 39. CAPSENSE™ CSD sensing shows. The AMUXBUS A and the GPIO cell switches (see SW3 in Figure 46. GPIO cell sourcing current to AMUXBUS A) forms this analog multiplexer. AMUXBUS A connects to all GPIOs that support CAPSENSE™. See the corresponding Device datasheet for a list of port pins that support CAPSENSE™. AMUXBUS A also connects the integrating capacitor C_MOD to the sigma-delta converter circuit. AMUXBUS B is used for shielding and is kept at V_REF when shield is enabled.

PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ supports shield electrodes for liquid tolerance and proximity sensing. CAPSENSE™ has a shielding circuit that drives the shield electrode with a replica of the sensor switching signal to nullify the potential difference between sensors and shield electrode. See Driven-shield signal and shield electrode Driven-shield signal and shield and Effect of liquid droplets and liquid stream on a self-capacitance sensor for details on how this is useful for liquid tolerance.

In the sensing circuit, the sigma delta converter keeps the AMUXBUS A at V_REF (see Sigma-delta converter). The GPIO cells generate the sensor waveforms by switching the sensor between AMUXBUS A and a supply rail (either V_DD or ground, depending on the configuration). The shielding circuit works in a similar way; AMUXBUS B is always kept at V_REF. The GPIO cell switches the shield between AMUXBUS B and a supply rail (either V_DDD or ground, the same configuration as the sensor). This process generates a replica of the sensor switching waveform on the shield electrode.

For a large shield layer with high parasitic capacitance, an external capacitor (Csh tank capacitor) is used to enhance the drive capacity of the shield electrode driver.

GPIO cell capacitance to current converter explains the GPIO cell configuration. In the Fifth-Generation architecture, the sensor is either interfaced to the AMUX (as before) or a new control MUX matrix which supports autonomous scanning (limited number of pins supported). The GPIO cells are configured as switched-capacitance circuits that convert sensor capacitances into equivalent charge transfer. Figure 60. GPIO cell structure shows the GPIO cell structure.

Four non-overlapping, out-of-phase clocks of frequency F_SW control the switches (SW1, SW2, SW3 and SW4) as Figure 61. Voltage across sensor capacitance shows.

IDACs are replaced by CDACs in the Fifth-Generation CAPSENSE™ architecture. It consists of two CDACs, a reference capacitor DAC and a compensation capacitor DAC. In each sense clock period the sensor capacitance, as mentioned in GPIO cell capacitance to charge converter, transfers charge to bothC_MOD in a way that it unbalances the voltage between the C_MOD’s. Both capacitor DACs are switched onto C_MOD multiple times during a sense clock period to balance the C_MOD’s back to their original voltage. Number of cycles required by the reference capacitor DAC to balance is proportional to the self-capacitance of the sensors.

This block generates the sense clock F_SW, and the modulation clock F_MOD, from the high-frequency system resource clock (HFCLK) or peripheral clock (PERI) depending on the PSoC™ device family.

It consists of a ratiometric converter and two CDACs, a reference capacitor DAC and a compensation capacitor DAC. In each sense clock period the sensor capacitance, as mentioned in GPIO cell capacitance to charge converter, transfers charge to both C_MOD in a way that it unbalances the voltage between the C_MOD’s. The Ratiometric converter controls the reference CDAC by switching it ON or OFF corresponding to the small voltage variations across two C_MOD’s to maintain the C_MOD’s voltage at same level. Number of cycles required by the reference capacitor DAC to balance the voltage between the C_MOD’s is proportional to the self-capacitance of the sensors.

The compensation capacitor is used to compensate excess mutual-capacitance from the sensor to increase the sensitivity. The number of times it is switched depends on the amount of charge the user application is trying to compensate (remove) from the sensor mutual-capacitance.

The ratiometric converter can operate in either single CDAC mode or dual CDAC mode.

• In the single CDAC mode, the reference CDAC is controlled by the ratiometric converter; the compensation CDAC is always OFF
• In the dual CDAC mode, the reference CDAC is controlled by the ratiometric converter; the compensation CDAC is always ON. Reference CDAC is capable of compensating up to 95%, results in increased signal as explained in Conversion gain and CAPSENSE signal

In the single CDAC mode, if C_ref is the value of the reference CDAC, the approximate value of raw count is given by Equation 18.

In the dual CDAC mode, the compensation CDAC is always ON. If C_compC_comp is the compensation CDAC, the equation for the raw count is given by Equation 19.

Where,

MaxCount = N_Sub.SnsClk_Div

N_Sub = Number of sub-conversions

SnsClk_Div = Sense clock divider

CompClk_Div = Compensation CDAC divider

C_S = Sensor capacitance

C_ref = Reference capacitance

C_comp = Compensation capacitance

As per Equation 18, the output raw count is proportional to the ratio of sensor capacitance to the reference capacitance, and hence the name Ratiometric Sensing.

Noise improvement is one of the main advantages of Fifth-Generation over previous generation of CAPSENSE™ technology. The dominant noise sources in the Fourth-Generation are current (I_MOD), reference voltage (V_REF), clock jitter (F_SW) (see Figure 53. Dual IDAC sourcing raw count). These noise sources have been removed for the Fifth-Generation (see Equation 19). The IDAC has been replaced with CDAC. The system has been made fully differential, so it does not need V_REF. The CAPSENSE™ architecture is no longer affected by jitter as the scan result is now based on the edges of the clock rather than the duration of the clock.

Another feature introduced in the Fifth-Generation is the control matrix (CTRLMUX) as shown in Figure 59. CAPSENSE™ CSD-RM (fifth-generation). The CTRLMUX enables autonomous scanning and provides immunity to on-chip IO noise. The CTRLMUX allows the CAPSENSE™ IP to directly handle the sensor inputs⁵ (in addition to the traditional GPIO mode), and hence supports autonomous scanning of the sensors without the CPU.

PSoC™™ 4 CAPSENSE™ supports shield electrodes for liquid tolerance and proximity sensing. The purpose of the shielding is to remove the parasitic capacitance between sensor and shield electrodes. See Driven-shield signal and shield electrode and Effect of liquid droplets and liquid stream on a self-capacitance sensor for details on how this is useful for liquid tolerance. The Fifth-Generation CAPSENSE™ architecture supports two shield modes – active and passive shielding.

The ratiometric converter gives an equivalent raw count which is proportional to the sensor mutual-capacitance after each scan. The ratiometric converter can operate in either single CDAC mode or dual CDAC mode.

• In the single CDAC mode, the reference CDAC is controlled by the ratiometric converter; the compensation CDAC is always OFF
• In the dual CDAC mode, the reference CDAC is controlled by the ratiometric converter; the compensation CDAC is always ON. Compensation CDAC is capable of compensating up to 95%, results in increased signal as explained in Conversion gain and CAPSENSE signal

In the single CDAC mode, if C_ref is the value of the reference CDAC, the approximate value of raw count is given by Equation 22.

In the dual CDAC mode, the compensation CDAC is always ON. If C_comp is the compensation CDAC, the equation for the raw count is given by Equation 23.

Where,

MaxCount = N_Sub.TxClk_Div

N_Sub = Number of sub-conversions

TxClk_Div = Tx clock divider

CompClk_Div = CDAC compensation divider

C_M = Mutual-capacitance of the sensor

C_ref = Reference capacitance

C_comp = Compensation capacitance

According to Equation 23, the output raw count is proportional to the ratio of mutual-capacitance of the sensor to the reference capacitance, and hence the name ratiometric sensing.

PSoC™ Creator provides a CAPSENSE™ component, which is used to create a capacitive touch system in PSoC™ by simply configuring this Component. The CAPSENSE™ component also provides an application programming interface (API) to simplify firmware development. Some PSoC™ 4 Bluetooth® LE and PSoC™ 6 MCU devices also support a CAPSENSE™ Gesture Component (see the corresponding Device datasheet to see if your device supports this Component).

Each CAPSENSE™ component has an associated datasheet that explains details about the Component. To open the Component datasheet, right-click the Component and select Open Datasheet.

The CAPSENSE™ component also has a Tuner GUI, called the Tuner GUI, to help with the tuning process.

The CapSense_ADC⁶ component is only applicable for the PSoC™ 4S-Series, PSoC™ 4100S Plus, PSoC™ 4100PS, and PSoC™ 6 MCU devices. This component should be used when both CAPSENSE™ and ADC operations are required. This component allows using the CAPSENSE™ block for ADC operation and touch functionality in a time-multiplexed manner.

Tuner helper is included with the CAPSENSE™ component and assists in tuning CAPSENSE™ parameters and monitoring sensor data such as raw count, baseline, and difference count. Refer the Component datasheet/middleware document for the detailed procedure on how to use Tuner GUI.

You can use the CAPSENSE™ example projects provided in PSoC™ Creator to learn schematic entry and firmware development. To find a CAPSENSE™ example project, go to the PSoC™ Creator start Page, click Find Code Example …, and select the appropriate architecture, as Figure 74. PSoC™ Creator example project shows. You can also filter for a project by writing partial or complete project name in the Filter by field.

ModusToolbox™ provides a CAPSENSE™ middleware, which can be used to create a capacitive touch system in PSoC™ by simply configuring parameters in the CAPSENSE™ configuration tool. The middleware also provides an application programming interface (APIs) to simplify firmware development. See the CAPSENSE™ middleware library for more details.

The CAPSENSE™ configurator tool in ModusToolbox™ is similar to that in PSoC™ Creator which is used to configure the CAPSENSE™ hardware and software parameters. For more details on configuring CAPSENSE™ in ModusToolbox™, see the ModusToolbox™ CAPSENSE™ configurator guide and CAPSENSE™ middleware library. Figure 75. CAPSENSE™ configurator tool in ModusToolbox™ shows how to open the CAPSENSE™ configuration tool in ModusToolbox™. Alternatively, it can also be opened from the Quick panel in the ModusToolbox™. For simplicity of documentation, this design guide shows selecting the CAPSENSE™ parameter in PSoC™ Creator CAPSENSE™ component.

This CSDADC middleware⁸ should be used when both the CAPSENSE™ and ADC operations are required. This middleware allows using the CAPSENSE™ hardware block for ADC operation and touch functionality in a time-multiplexed manner. It could be used for all three sensing modes that is, CSD, ADC, and CSX. See the CSDADC middleware library documentation for more details.

The CSDIDAC middleware allows you to use the CAPSENSE™ IDAC in a standalone mode. You can use this middleware if you are not using CAPSENSE™ middleware or if you are using only one IDAC for CAPSENSE™. See the CSDADC middleware library documentation.

ModusToolbox™ also supports a GUI tool that can be used for tuning CAPSENSE™ parameters. This tool can be opened from the Device configurator by selecting Launch CapSense Tuner as shown in Figure 75. CAPSENSE™ configurator tool in ModusToolbox™. See the CAPSENSE™ tuner guide documentation.

To quickly start the CAPSENSE™ system design, start with the example projects provided in ModusToolbox™. You can find a CAPSENSE™ example project by navigating to File > New > ModusToolbox Application. Choose the appropriate Board Support Package with a device. Figure 76. Creating CAPSENSE™ CSD Button example project in ModusToolbox™ shows creating a CAPSENSE™ CSD Button example starter code in ModusToolbox™ from the list of available code examples.

The CAPSENSE™ algorithm is a combination of hardware and firmware blocks inside PSoC™. Therefore, it has several hardware and firmware parameters required for proper operation. These parameters need to be tuned to optimum values for reliable touch detection and fast response.

SmartSense is a CAPSENSE™ tuning method that automatically sets sensing parameters for optimal performance, based on user-specified finger capacitance values, and continuously compensates for system, manufacturing, and environmental changes.

Some advantages of SmartSense, as opposed to manual tuning are:

• Reduced design cycle time: The design flow for capacitive touch applications involves tuning all of the sensors. This step can be time consuming if there are many sensors in your design. In addition, you must repeat the tuning when there is a change in the design, PCB layout, or mechanical design. Auto-tuning solves these problems by setting all of the parameters automatically. Figure 77. Design flow with and without SmartSense shows the design flow for a typical CAPSENSE™ application with and without SmartSense

• Performance is independent of PCB variations: The parasitic capacitance, C_P, of individual sensors can vary due to process variations in PCB manufacturing, or vendor-to-vendor variation in a multi-sourced supply chain. If there is significant variation in C_P across product batches, the CAPSENSE™ parameters must be re-tuned for each batch. SmartSense sets parameters for each device automatically, hence taking care of variations in C_P
• Ease of use: SmartSense is faster and easier to use because only a basic knowledge of CAPSENSE™is needed

Note that SmartSense can be used in multiple ways:

1. SmartSense (Full auto-tune) – This is the quickest way to tune. This method calibrates CAPSENSE™ hardware and software parameters automatically at runtime. This is the recommended method for most designs
2. SmartSense (Hardware parameters only) – This method auto-tunes all hardware parameters of CAPSENSE™, but allows to set user-defined threshold values (see ). This method consumes less flash/RAM resources than SmartSense (Full Auto-Tune). Also, this method avoids the extra processing needed for automatic threshold calculation and hence allows lower power consumption for a given scan rate. Use this method for low-power or noisy designs or in cases with constrained memory requirements
3. SmartSense for initial tuning – You may also use SmartSense for initial tuning, to quickly find the best settings for a CAPSENSE™ board and then change to manual tuning. This method is useful for cases with strict requirements on response time or power consumption. This is a quick method to find the best settings, instead of starting manual tuning from scratch. Refer to the section Using SmartSense to determine hardware parameters for more details

4. Table 7. CAPSENSE™ parameters auto-tuned in SmartSense

   Parameter	Full auto-tune mode	Hardware parameters only mode
   Scan resolution	Calculated once on CAPSENSE™ initialization.
   Compensation IDAC
   Modulator IDAC
   Sense clock frequency
   Modulator clock frequency
   Finger threshold	Calculated once on CAPSENSE™ initialization based on the selected finger capacitance and updated after each sensor scan.	Manual selection (see ).
   Noise threshold
   Hysteresis
   Negative noise threshold
   Low baseline reset

In SmartSense Full Auto-tune mode, the only parameter that needs to be tuned by the user is the Finger Capacitance parameter. The Finger Capacitance parameter (C_F) indicates the minimum value of finger capacitance that should be detected as a valid touch by the CAPSENSE™ Component. Whenever the actual C_F that is added when the finger touches the button sensor is greater than the value specified for the Finger Capacitance parameter in the Component configuration window, the sensor status will change to ‘1’; however, if the actual C_F added by the finger touch is less than the value specified in the Component configuration window, the sensor status will remain ‘0’. The way of tuning the finger capacitance is different for button and slider widgets.

See for the recommended values for thresholds when the CSD tuning method is SmartSense (Hardware parameters only).

See Using SmartSense to determine hardware parameters for more details.

SmartSense technology allows a device to calibrate itself for optimal performance and complete the entire tuning process automatically. This technology will meet the needs of most designs, but in cases where SmartSense does not work or there are specific SNR or power requirements, the CAPSENSE™ parameters can be adjusted to meet system requirements. This can be achieved by manual tuning.

Some advantages of manual tuning, as opposed to SmartSense auto-tuning are:

• Strict control over parameter settings: SmartSense sets all the parameters automatically. However, there may be situations where you need to have strict control over the parameters. For example, use manual tuning if you need to strictly control the time PSoC™ takes to scan a group of sensors or strictly control the sense clock frequency of each sensor (this can be done to reduce EMI in systems)
• Supports higher parasitic capacitances: If the parasitic capacitance is higher than the value supported by SmartSense, you should use manual tuning. See the Component datasheet/middleware document for more details on the supported range of parasitic capacitance by SmartSense

The manual tuning process can be summarized in the following three steps and is shown in Figure 80. Manual tuning process overview.

Set initial values of Selecting CAPSENSE™ hardware parameters using SmartSense (see Using SmartSense to determine hardware parameters) or determine the values manually.

Tune CAPSENSE™ component hardware parameters to ensure that Signal-to-noise is greater than 5:1 with a signal of at least 50 counts while meeting the system timing requirements.

Set optimum values of Selecting CAPSENSE™ software parameters.

The following sections describe the fundamentals of manual tuning and the above three steps in detail. Knowledge of the CAPSENSE™ architecture in PSoC™ is a prerequisite for these sections. See Capacitive touch sensing method and CAPSENSE™ generations in PSoC™ 4 and PSoC™ 6. The main difference in CAPSENSE™ architecture across different generations are listed in .

Depending upon the sensing method selected, the manual tuning procedure will differ. See CSD sensing method (third- and fourth-generation), CSX sensing method (third- and fourth-generation) chapter for their respective manual tuning procedures. You can skip these sections if you are not planning to use manual tuning in your design. Figure 80. Manual tuning process overview shows a general manual tuning procedure.

* To review the hardware design, see the Sensor construction and PCB layout guidelines sections in the Design considerations chapter.

This section explains the basics of manual tuning using CSD sensing method. It also explains the hardware and software parameters that influence CSD sensing method and procedure of manual tuning for button, slider, touchpad and proximity widgets.

This chapter explains the basics of manual tuning using the CSX sensing method. It also explains the hardware parameters that influence a manual tuning procedure.

This chapter explains the basics of manual tuning using CSD-RM sensing method (Fifth-Generation). It also explains the hardware and software parameters that influence the CSD-RM sensing method and the procedure of manual tuning for button, slider, touchpad and proximity widgets.