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[FAQ] FDC1004 Capacitive Sensing FAQs

Genius 17945 points

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Part Number: FDC1004

 What are the differences between Capacitive Sensing Versus Capacitive Touch Solutions.

Texas Instruments provides solutions for capacitive sensing and capacitive touch applications, which share some important similarities and some crucial differences. Capacitive sensing applications can require relatively large target distances and/or higher resolution than capacitive touch applications.

The table below offers a brief comparison between the similarities and differences between these two applications

Requirements

Capacitive Sensing

Capacitive Touch

Channel count

Low (< 4)

High (> 8)

Resolution

High

Low

Typical distance

Up to 70 cm

2 to 3 mm

Sensitivity

< 1 fF

10s to 100s fF

Requires contact

No

Yes

Power consumption

μA range

μA to mA range

For more information on capacitive touch solutions, please consider TI's capTIvate as the best fit for this application.

        http://www.ti.com/microcontrollers/msp430-ultra-low-power-mcus/capacitive-sensing-mcus-overview.html

                         

What applications can/can’t be supported by capacitive sensing?

  1. Liquid Level Sensing
    For most non-conductive liquid level sensing applications (including water), the FDC1004 should be used. The FDC1004 has an active shield driver which helps the system against interference from environmental factors.

  2. Non-Metal Proximity Sensing
    The FDC1004 is the best choice, since the FDC2x1x does not have a shield driver, can and requires advanced system level expertise.

  3. What applications do not work with TI's capacitive sensing technology?
    Metal detection - to detect metal, TI's inductive sensing solutions are a better option.
    See the TI E2E Inductive Sensing FAQ  Inductive Sensing FAQ 

How do I get started with Capacitive Sensing?

A list of learning and design resources, sorted by subject, are given below.

Subject

App Note Title

App Note URL

Introductory App Notes

Common Inductive and Capacitive Sensing Applications

https://www.ti.com/lit/pdf/slya048

Basics of Capacitive Sensing with FDC1004

 https://www.ti.com/lit/pdf/snoa927

Liquid Level Sensing App Notes

Capacitive Sensing: Ins and Outs of Active Shielding 

https://www.ti.com/lit/pdf/snoa926

Capacitive Sensing: Out-of-Phase Liquid Level Technique

https://www.ti.com/lit/pdf/snoa925

Capacitive Sensing: Direct vs Remote Liquid-Level Sensing Performance Analysis

https://www.ti.com/lit/pdf/snoa935

Liquid Level Sensing with the Immersive Straw Approach

https://www.ti.com/lit/pdf/snoa934

How to Calibrate FDC1004 for Liquid Level Sensing Applications

https://www.ti.com/lit/pdf/snoa958

Proximity sensing

Capacitive Proximity Sensing Using the FDC1004

https://www.ti.com/lit/pdf/snoa928

General App Notes, Technical Articles and Blogs

Derivative Integration Algorithm for Proximity Sensing

https://www.ti.com/lit/pdf/snoa939

Ground Shifting in Capacitive Sensing Applications

https://www.ti.com/lit/pdf/SNOA952

Power Reduction Techniques for the FDC2214/2212/2114/2112 in Capacitive Sensing Applications

https://www.ti.com/lit/pdf/SNOA943

Capacitive sensing: simple algorithm for proximity sensing

https://e2e.ti.com/BLOGS_/B/ANALOGWIRE/ARCHIVE/2015/11/23/CAPACITIVE-SENSING-SIMPLE-ALGORITHM-FOR-PROXIMITY-SENSING

Capacitive sensing: which architecture should you choose?

https://e2e.ti.com/blogs_/b/analogwire/archive/2015/10/20/capacitive-sensing-which-architecture-should-you-choose

TI Designs

Capacitive Based Liquid Level Sensing - TIDA-00317 (FDC1004 , MSP430F5528 )

http://www.ti.com/tool/TIDA-00317

Backlight and Smart Lighting Control by Ambient Light and Proximity Sensor Reference Design - TIDA-00373 (FDC1004 , HDC1000 , HDC1008 )

https://www.ti.com/tool/TIDA-00373

Automotive Capacitive Proximity Kick to Open Detection Reference Design TIDA-00506 (FDC1004)

https://www.ti.com/tool/TIDA-00506

Capacitive-Based Human Proximity Detection for System Wake-Up & Interrupt Reference Design - TIDA-00220 (FDC1004 , LM3630A , LP5907 )

https://www.ti.com/tool/TIDA-00220

EVMs

FDC1004EVM - 4 Channel Capacitive to Digital Converter Evaluation Module

https://www.ti.com/tool/FDC1004EVM

Software

Capacitive Sensing Sample Code (Energia)

http://www.ti.com/lit/zip/snvc187

Sensing Solutions EVM GUI Tool

http://www.ti.com/lit/zip/snoc028

   

What are the differences between the FDC1004 and the FDC2212/2214?

The table below shows & compares the major features of the two devices.

FDC1004

FDC2212/2214

Number of Channels

4

2 or 4

Architecture

Switched Cap

Resonant LC Tank

Supply Voltage

3.3

3.3

I active

0.95mA

2.1mA

Sensor Current

0

6mA

Sensor driving Frequency

25 kHz

0.1Mhz - 10 MHz

Maximum Sensor Input

115pF

250nF @ 10Khz / 25pF @ 10 MHz

Sensor input range w/respect to input offset calibration

±15pF

NA

Input Offset Calibration

100pF

N/A

Integrated Shield Driver

400pF

N/A

Driver Architecture

Continuous CLK driver

Discontinuous Sin Driver

Effective resolution

16 bits

12/28 bits depending on the LC frequency

Gain error

0.20%

N/A

Gain Error over temp

37.5 ppm/C

Depends on External LC

DC PSRR

13.6fF/V

N/A

EMI

Better

Poor, needs external passives

Configurability

Contained

High SW and HW

Package

QFN/TSSOP

QFN

 

  • As the table shows, the FDC1004 input is a switch-cap topology while the FDC2x12/4 uses a resonant tank. The major advantages of the FDC1004 is its integrated shield driver, which can improve the EMI/noise immunity of your circuit, and its driver architecture, which greatly reduce EMI emissions, compared to the FDC2x12/4. 

FDC1004 frequently asked questions:

  • When is the FDC1004 a bad fit for my liquid level sensing application?
    The FDC1004 does not work with conductive liquid. The FDC1004 works well for most other liquid level sensing applications, including water. For more information, see the topic Liquid Level Sensing App Notes above for a list of supporting app notes.

  • Should I use a single-ended or a differential measurement?
    Both options work can work for liquid level sensing. The advantage of the differential measurement is that it helps with immunity to environmental conditions. For more information please see the app note Capacitive Sensing: Out-of-Phase Liquid Level Technique https://www.ti.com/lit/pdf/snoa925

  • Can the FDC1004 be used for proximity sensing applications?
    The FDC1004 can be used for proximity detection, and detection of simple gestures. For more information on using the FDC1004 for proximity detection, please see the app note Capacitive Proximity Sensing Using the FDC1004 https://www.ti.com/lit/pdf/snoa928 , or the reference designs https://www.ti.com/tool/TIDA-00506 & https://www.ti.com/tool/TIDA-00220

 Capacitive sensing applications with the FDC1004 include:

1. Independent channels
The FDC1004 features 4 independent channels that are sampled sequentially in a time-multiplexed manner. Typical applications include rain sensing, proximity/gesture detection, and water/ice/snow detection.

Figure 1. Independent Channel use Case for Gesture Sensing Application

2. Differential or ratio-metric measurements
Differential measurements are performed to obtain an accurate capacitance measurement difference between two sensors. This is most applicable to environmental factors that can cause variations in capacitance, such as direct, immersive sensing, or remote liquid sensing.

 Figure 2. Differential or Ratiometric Measurements Example, Liquid Level


3. Remote sensing
Physical distances between the sensor and the device can be a major issue when accurate capacitive measurements are needed. To compensate for long signal paths, the FDC1004 allows parasitic capacitance compensation up to 100 pF which gives the FDC1004 the ability to drive a twisted pair up to 1600 m (60 fF/m) or a coax cable up to 1.5 m (66 pF/m).
Figure 3. Remote Sensing Example
4. Time-varying offset measurements
The FDC1004 can be used in the case where time-varying offset measurements are required to be monitored. A replica sensor adjusts for changes in offset from factors like humidity, environment, and water/ice/snow.
Figure 4. Time-Varying Offset Measurements Example

Regards,

John Miller
Sensing Applications Engineer