HOD CAP Click

How does it work?

HOD CAP Click is based on the AS8579, a capacitive sensor from ams OSRAM. The AS8579 is a sensor that detects the change of capacity in different applications, as it measures the relative change of the impedance, which can be used for human being detection besides other usages. The sensors’ primary function is the transceiver Analog Front-End (AFE) architecture. The AFE function senses the impedance of the output load by using transmitter and receiver blocks. The transmitter block supplies a sine wave across the load, which the receiver blocks capture. The current change is sensed, and the response is converted to a voltage and then demodulated into in-phase (I) and quadrature (Q) components. These I and Q components are later filtered and converted by a 10-bit ADC to digital words.

The HOD CAP Click comes with a 10-pin header for sense outputs labeled SEN0-9. Five of the ten output pins (SEN5-9) are additionally filtered by the SEN Line Filter circuits. You can set the on-chip ADC in a Single or Continuous Conversion depending on the task. The first causes ADC to wait for the system settling time before starting sampling, while the latter causes the ADC to take successive sample accumulations. Using the CLK SEL jumper, you can provide the system clock with a frequency in two ways. The selected option INT uses the internal PWM duty cycle of the host MCU to provide a desired frequency, which can be in the range of 3 up to 50MHz. The other option uses onboard 48MHz crystal.

In addition, the AS8579 comes with parasitic capacitance protection. A header consisting of VAR SEN, FIX SEN, and GND pins can be used for that purpose. The VAR SEN is a cable shielding driver and should be connected to a cable shielding to avoid parasitic capacitance influence from shielding. The FIX SEN should be connected to a PCB shield layer to avoid parasitic capacitance influences from the PCB shield layer. Otherwise, both should be connected to the GND. For the factory testing option, you can short the R5. The HOD CAP Click uses the standard 4-Wire SPI serial interface to communicate with the host MCU with a clock frequency of up to 8MHz.

This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VIO SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. However, the Click board™ comes equipped with a library containing easy-to-use 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 HOD CAP 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	CLK	Clock Frequency
	NC	2	RST	INT	15	NC
SPI Chip Select	CS	3	CS	RX	14	NC
SPI Clock	SCK	4	SCK	TX	13	NC
SPI Data OUT	SDO	5	MISO	SCL	12	NC
SPI Data IN	SDI	6	MOSI	SDA	11	NC
Power Supply	3.3V	7	3.3V	5V	10	5V	Power Supply
Ground	GND	8	GND	GND	9	GND	Ground

Onboard settings and indicators

HOD CAP Click electrical specifications

Software Support

We provide a library for the HOD CAP 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 HOD CAP Click driver.

Key functions

• hodcap_get_i_q_data HOD CAP gets the I and Q data function.

• hodcap_mux_channel_selection HOD CAP MUX channel selection function.

• hodcap_wait_adc_data_ready HOD CAP wait ADC data ready function.

Example Description

This library contains API for the HOD CAP Click driver. The demo application sets the sensor configuration and detects the changes in capacity by measuring the relative change of the impedance for each channel.

void application_task ( void ) 
 {  
     static uint16_t i_data, q_data; 
     log_printf( &logger, " tI/Q data rn" ); 
     for ( uint8_t sen_num = 0; sen_num < HODCAP_TOTAL_NUMBER_OF_CHANNELS; sen_num++ ) 
     { 
         if ( HODCAP_OK == hodcap_mux_channel_selection ( &hodcap, sen_num ) ) 
         { 
             if ( ( HODCAP_OK == hodcap_wait_adc_data_ready( &hodcap ) ) && 
                  ( HODCAP_OK == hodcap_get_i_q_data( &hodcap, &i_data, &q_data ) ) ) 
             { 
                 log_printf( &logger, " SEN%d -> ", sen_num ); 
                 log_printf( &logger, " I : %u |", i_data ); 
                 log_printf( &logger, " Q : %u rn", q_data );        
                 Delay_ms( 100 ); 
             } 
         } 
     } 
     log_printf( &logger, "________________________rn" ); 
     Delay_ms( 2000 ); 
 }

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.HODCAP

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.