Touch Key 4 Click is a capacitive touch sensing Click board™, with the advanced touch/proximity sensor IC. It has three independently configurable channels and can work in several operating modes, including multiple button pattern detection mode, combo mode, press and hold detection mode, power button mode, and more. Capacitive touch sensor inputs are protected from false detection, which can be caused by the noise and RF interferences, providing a very reliable touch sensing functionality. Electrostatic Discharge (ESD) protection up to 8kV ensures that no ESD failures will ever occur while interacting with the sensor surface.

Equipped with three sensor channels, which are compensated for parasitic capacitances of the system, have an automatic recalibration feature, and are protected against ESD up to 8kV, Touch Key 4 Click offers very reliable and accurate sensing for any application that uses capacitive touch sensing functions, such as desktop or notebook computers, LCD/TFT monitors, various types of consumer electronics, home appliances, and other applications that can benefit of having a reliable and feature-rich touch activated user interface.

The capacitive sensor IC used on the Touch Key 4 Click is the CAP1293, 3 channel capacitive touch sensor with proximity detection, from Microchip. This IC has three independently configurable capacitive touch channels with the auto-calibration function. It uses the I2C protocol for the communication, with the I2C bus pins routed to the respective mikroBUS™ pins: SMCLK is the I2C clock pin, routed to the SCK pin of the mikroBUS™ and the SMDATA is the I2C data pin, routed to the SDA pin of the mikroBUS™. Additionally, there is an #ALERT pin routed to the mikroBUS™ INT pin, which allows interrupts to be triggered on the host MCU.

The Click board itself has three PCB pads, used to sense touch or proximity events. These pads are the only elements on the top side of the board, allowing installation of the protective acrylic glass layer. The capacitive sensor channels feature programmable sensitivity threshold and an automatic recalibration, used to compensate for environmental changes. The device can work in several power modes, having separate input settings for the Active and Standby mode. The recalibration procedure can be triggered either automatically, or on-demand, and it is used to set the base register value for the “not touched” state of the input channel.

The CAP1293 IC also integrates sections that provide an efficient interference protection. The EMI and RFI detection sections provide protection by discarding the corrupted bytes if the detected noise threshold is exceeded. Also, false input readings, such as the negative values and “stuck button” events are handled by the internal algorithms, which will set the respective bits to indicate the problem, and can be set to trigger a recalibration procedure.

There are three power modes of operation:

• Fully Active mode, which monitors all the enabled input channels in cyclic order. Touch detection threshold can be individually set for each channel, and the averaging (integration) and cycle time are set via the appropriate register. All registers are available for both reading and writing.
• Standby mode, which cycles through the channels, enabled by the dedicated Standby Channel Register. There is only one threshold for all the enabled channels, determined by the dedicated Standby Threshold Register. Communication will be still functional and the device can be set to a Fully Active mode. This mode uses less power than the Fully Active mode, depending on the settings of the cycle time and integration time.
• Combo mode, which is a mixture of the Active and Standby modes. The device cycles through both the channels enabled in the Active mode, as well as the inputs enabled in the Standby mode. This mode allows mixture between proximity and touch detection, as it has two separate gain level registers - one register controls gain for the Active mode enabled channels, while the other register is for the Standby mode enabled channels.
• Deep Sleep mode, which consumes the least power. In this mode, all the input channels are disabled. The communication is still possible. As soon as the communication ends, the device reverts to Deep Sleep mode, if not instructed otherwise.

In general, the device always reverts to a power saving mode when idling. If the programmed cycling time through all the enabled channels is long enough, the sampling of all the enabled channels will be finished before the cycle ends. When this happens, the device will revert to a power saving mode, waiting for another cycle to begin. If there is not enough time to sample all the channels, the device will not revert to a power saving mode. This will affect the overall power consumption.

Multiple touch pattern detection (MTPD) is used to set the pattern which will generate a touch event. This pattern may consist of multiple specific sensors touched at once, a minimal number of touched sensors, or when their noise flag bit is set in the status register. This function can be used to detect a closed lid or similar event.

The interrupt engine allows to differentiate between the simple touch and touch and hold events. The interrupt can be generated once when a pad touch is detected/released, or it can be repeatedly generated while the pad is touched. A special case of touch detection is the Power Button mode. This mode requires the button to be held pressed for a programmed interval of time before an interrupt is generated. This allows for a simple Power Button functionality to be implemented in any application. The interrupt can be generated for various other events, such as the failure to calibrate event and similar auxiliary events.

The press and hold mode is very useful for developing volume control type of applications. The programmable interval timer is started after the first touch event on a specific channel, and if no release event is detected after the timer expires, the interrupt is generated, in the programmed intervals. This can be used to implement volume up/down buttons, light dimming buttons, and similar applications.

Any interrupt event will drive the #ALERT pin to a LOW logic state. This pin is routed to the mikroBUS™ INT pin and it is used to trigger an interrupt event on the host MCU.

More information about the registers and their functions can be found in the CAP1293 IC datasheet. However, the provided Click library offers a function for easy and simple control of the Touch Key 4 Click. The provided application example demonstrates their functionality and it can be used as a reference for custom projects.

• Interface: I²C
• Compatibility: mikroBUS™
• Dimensions: 42.9 x 25.4mm
• Input Voltage: 3.3V or 5V

• Schematic
• CAP1293 Datasheet
• mikroSDK
• GitHub