TouchClamp Click

How does it work?

TouchClamp Click is based on the MPR121, a proximity capacitive touch sensor controller from NXP Semiconductors. The MPR121 uses seven electrodes/capacitance sensing inputs, four of which are multifunctional for LED driving (H, C, B, A) and GPIO. One electrode is an extra capacitive button in the middle of the board labeled H. It also features the 8th simulated electrode, which represents the simultaneous charging of all electrodes connected together. The MPR121 has integrated independent autocalibration and autoconfiguration for each electrode input and separate touch and release trip thresholds for each, providing hysteresis and electrode independence. The easiest way to experiment with TouchClamp click is to use wires with alligator clips. Let your imagination roam free when choosing conductive objects such as cans, fruit, jar lids, and more.

The MPR121 chip has several features in addition that simplify development and integration. First, it applies three levels of digital filtering to the raw ADC data to remove high and low-frequency noise, ensuring that the interrupts are properly registered in a broad range of applications. The auto-calibration function, according to the vendor’s datasheet, “continually learns the background baseline capacitance of each individual electrode, so the system only has to program the amount of small change from these baselines that represents a touch or release.” The auto-configuration uses the given target charge level so the chip can automatically run to get an optimized charge current and charge time setting for each electrode without knowing the specific capacitance value on the electrode input.

The capacitance sensing uses a constant DC current capacitance sensing scheme and can measure capacitances ranging from 10pF to over 2000pF, with resolutions up to 0.01pF. The voltage measured on the input sensing node is inversely proportional to the capacitance and is sampled by an internal 10-bit ADC. The touch sensing compares the baseline value with the current immediate electrode data to determine if a touch or a release has occurred, with the ability to set a touch/release threshold. The proximity sensing acts as the near proximity sensing system, where all electrodes can be summoned together to create a single large electrode, thus covering a much larger area. Touch sensing and proximity sensing can be used at the same time. Among 12 electrodes, eight of them can be used as a GPIO and can be used to drive LEDs or for GPIO.

The TouchClamp Click uses an I2C 2-Wire interface to communicate with the host MCU. It also has an ADDR SEL jumper to choose between the two available I2C addresses and can be connected to VDD or VSS (VSS position set by default). In addition, the TouchClamp Click comes with an interrupt INT pin which is triggered anytime a touch or release is detected.

This Click board™ can only be operated with a 3.3V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. However, the Click board™ comes equipped with a library containing functions and an example code that can be used, as a reference, for further development.

Specifications

Pinout diagram

This table shows how the pinout on TouchClamp Click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin					Pin	Notes
	NC	1	AN	PWM	16	NC
	NC	2	RST	INT	15	INT	Interrupt pin
	NC	3	CS	RX	14	NC
	NC	4	SCK	TX	13	NC
	NC	5	MISO	SCL	12	SCL	I2C Clock
	NC	6	MOSI	SDA	11	SDA	I2C Data
	NC	7	3.3V	5V	10	NC
Ground	GND	8	GND	GND	9	GND	Ground

Onboard settings and indicators

TouchClamp Click electrical specifications

Software Support

We provide a library for the TouchClamp Click as well as a demo application (example), developed using MIKROE compilers. The demo can run on all the main MIKROE development boards.

Package can be downloaded/installed directly from NECTO Studio Package Manager (recommended), downloaded from our LibStock™ or found on Mikroe github account.

Library Description

This library contains API for TouchClamp Click driver.

Key functions

• Get touch data function.

Example Description

This demo-app shows the touch position using TouchClamp click.

 void application_task ( void ) 
 { 
     touch_data = touchclamp_get_touch_data( &touchclamp ); 

     if ( touch_data_old != touch_data ) 
     { 
         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_H ) 
             log_printf( &logger, "  - - - - - - - Hrn" ); 

         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_G ) 
             log_printf( &logger, "  - - - - - - G -rn" ); 

         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_F ) 
             log_printf( &logger, "  - - - - - F - -rn" ); 

         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_E )                        
             log_printf( &logger, "  - - - - E - - -rn" ); 

         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_D )                        
             log_printf( &logger, "  - - - D - - - -rn" ); 

         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_C )                        
             log_printf( &logger, "  - - C - - - - -rn" ); 

         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_B )                        
             log_printf( &logger, "  - B - - - - - -rn" ); 

         if ( touch_data == TOUCHCLAMP_TOUCH_POSITION_A )                        
             log_printf( &logger, "  A - - - - - - -rn" ); 

         touch_data_old = touch_data; 
     } 
 }

The full application code, and ready to use projects can be installed directly from NECTO Studio Package Manager (recommended), downloaded from our LibStock™ or found on Mikroe github account.

Other Mikroe Libraries used in the example:

• MikroSDK.Board
• MikroSDK.Log
• Click.TouchClamp

Additional notes and informations

Depending on the development board you are using, you may need USB UART click, USB UART 2 Click or RS232 Click to connect to your PC, for development systems with no UART to USB interface available on the board. UART terminal is available in all MIKROE compilers.

mikroSDK

This Click board™ is supported with mikroSDK – MIKROE Software Development Kit. To ensure proper operation of mikroSDK compliant Click board™ demo applications, mikroSDK should be downloaded from the LibStock and installed for the compiler you are using.

For more information about mikroSDK, visit the official page.