The AD7156 delivers a complete signal processing solution for capacitive sensors, featuring an ultralow power converter with fast response time.
The AD7156 uses an Analog Devices, Inc., capacitance-to-digital converter (CDC) technology, which combines features important for interfacing to real sensors, such as high input sensitivity and high tolerance of both input parasitic ground capacitance and leakage current.
The integrated adaptive threshold algorithm compensates for any variations in the sensor capacitance due to environmental factors like humidity and temperature or due to changes in the dielectric material over time.
By default, the AD7156 operates in standalone mode using the fixed power-up settings and indicates detection on two digital outputs. Alternatively, the AD7156 can be interfaced to a micro-controller via the serial interface, the internal registers can be programmed with user-defined settings, and the data and status can be read from the part.
The AD7156 operates with a 1.8 V to 3.6 V power supply. It is specified over the temperature range of −40°C to +85°C.
The goal of this project (Microcontroller No-OS) is to be able to provide reference projects for lower end processors, which can't run Linux, or aren't running a specific operating system, to help those customers using microcontrollers with ADI parts. Here you can find a generic driver which can be used as a base for any microcontroller platform and also specific drivers for different microcontroller platforms.
The driver contains two parts:
There are three functions which are called by the AD7156 driver:
I2C driver architecture
The following functions are implemented in this version of AD7156 driver:
|void AD7156_GetRegisterValue(unsigned char* pReadData, unsigned char registerAddress, unsigned char bytesNumber)||Performs a burst read of a specified number of registers.|
|void AD7156_SetRegisterValue(unsigned short registerValue, unsigned char registerAddress, unsigned char bytesNumber)||Writes data into one or two registers.|
|unsigned char AD7156_Init(void)||Initializes the communication peripheral and checks if the device is present.|
|void AD7156_Reset(void)||Resets the device.|
|void AD7156_SetPowerMode(unsigned char pwrMode)||Sets the converter mode of operation.|
|void AD7156_ChannelState(unsigned char channel, unsigned char enableConv)||Enables or disables conversion on the selected channel.|
|void AD7156_SetRange(unsigned channel, unsigned char range)||Sets the input range of the specified channel.|
|float AD7156_GetRange(unsigned channel)||Reads the range bits from the device and returns the range in pF.|
|void AD7156_SetThresholdMode(unsigned char thrMode, unsigned char thrFixed)||Selects the threshold mode of operation.|
|void AD7156_SetThreshold(unsigned char channel, float pFthr)||Writes to the threshold register when threshold fixed mode is enabled.|
|void AD7156_SetSensitivity(unsigned char channel, float pFsensitivity)||Writes a value(pF) to the sensitivity register. This functions should be used when adaptive threshold mode is selected.|
|void AD7156_ReadChannels(unsigned short* ch1, unsigned short* ch2)||Reads the 12-bit samples form both channels.|
|unsigned short AD7156_ReadOneChannel(unsigned char channel)||Reads a 12-bit sample from the selected channel.|
|void AD7156_ReadCapacitance(float* ch1, float* ch2)||Read data form both channels and converts it to picofarads(pF).|
|float AD7156_ReadChannelCap(unsigned char channel)||Reads a sample and converts the data to picofarads(pF).|
This section contains a description of the steps required to run the AD7156 demonstration project on a Renesas RL78G13 platform using the PmodCDC1.
A PmodCDC1 has to be interfaced with the Renesas Demonstration Kit (RDK) for RL78G13:
PmodCDC1 J1 connector Pin SCL → YRDKRL78G13 J11 connector Pin 9 PmodCDC1 J1 connector Pin SDA → YRDKRL78G13 J6 connector Pin 23 PmodCDC1 J1 connector Pin GND → YRDKRL78G13 J11 connector Pin 5 PmodCDC1 J1 connector Pin VCC → YRDKRL78G13 J11 connector Pin 6
The reference project samples the input capacitance on both channels and simultaneously checks if any of the two buttons are pressed or released. The two horizontal bars show how much pressure is applied on the two buttons on the pmod. CH1 has 2pF input range and CH2 has 4pF input range.
This section presents the steps for developing a software application that will run on the Renesas Demo Kit for RL78G13 for controlling and monitoring the operation of the ADI part.
This section contains a description of the steps required to run the AD7156 demonstration project on a Renesas RX63N platform using the PmodCDC1.
A PmodCDC1 has to be interfaced with the Renesas Demonstration Kit (RDK) for RX63N:
PmodCDC1 J1 connector Pin SCL ? YRDKRX63N JN2 connector Pin 23 PmodCDC1 J1 connector Pin SDA ? YRDKRX63N JN2 connector Pin 22 PmodCDC1 J1 connector Pin GND ? YRDKRX63N J15 connector Pin 5 PmodCDC1 J1 connector Pin VCC ? YRDKRX63N J15 connector Pin 6
The reference project samples the input capacitance on both channels and simultaneously checks if any of the two buttons are pressed or released.
This section presents the steps for developing a software application that will run on the Renesas Demo Kit for RX63N for controlling and monitoring the operation of the ADI part.