This version (05 Feb 2014 19:01) was approved by Lars-Peter Clausen.The Previously approved version (13 Nov 2012 15:10) is available.Diff

Supported Devices

Evaluation Boards


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.


  • Buttons and switches
  • Proximity sensing
  • Contactless switching
  • Position detection
  • Level detection
  • Portable products

01 Oct 2012 11:36 · Dragos Bogdan

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.

Driver Description

The driver contains two parts:

  • The driver for the AD7156 part, which may be used, without modifications, with any microcontroller.
  • The Communication Driver, where the specific communication functions for the desired type of processor and communication protocol have to be implemented. This driver implements the communication with the device and hides the actual details of the communication protocol to the ADI driver. The Communication Driver has a standard interface, so the AD7156 driver can be used exactly as it is provided.

There are three functions which are called by the AD7156 driver:

  • I2C_Init() – initializes the communication peripheral.
  • I2C_Write() – writes data to the device.
  • I2C_Read() – reads data from the device.

I2C driver architecture

The following functions are implemented in this version of AD7156 driver:

Function Description
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.
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.
unsigned short AD7156_ReadChannelData(unsigned char channel) Reads a 12-bit sample from the selected channel.
unsigned short AD7156_WaitReadChannelData(unsigned char channel) Waits for a finished CDC conversion and reads a 12-bit sample from the selected channel.
float AD7156_ReadChannelCapacitance(unsigned char channel) Reads a sample the selected channel and converts the data to picofarads(pF).
float AD7156_WaitReadChannelCapacitance(unsigned char channel) Waits for a finished CDC conversion the selected channel, reads a sample and converts the data to picofarads(pF).
resources/tools-software/uc-drivers/ad7156.txt · Last modified: 28 Jun 2013 10:04 by Lucian Sin