[FAQ] FDC1004 Capacitive Sensing FAQs

 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

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

See the Getting Started Guide and a selection of CapTIvate Devices here.

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.

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

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

• 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.

Physical distances between sensor and the device an be a major issue when accurate capacitive measurements are needed.
To compensate for long signal paths, the FC1004 allows parasitic capacitance compensation up to 100pF which gives the
FDC1004 the ability to drive a twisted pair up to 1600 meters (60 fF/m) or a coax cable up to 1.5m (66 pF/m).

A Detailed Look at the FDC1004

The following pages give a more detailed information on the FDC1004 for the following topics:

• Capacitive sensing basics
• Application overview
  1. Liquid level sensing
  2. Position sensing
  3. Swipe function
• High-level considerations for a design
• Device architecture, features & major specs
• EVM GUI configurations
• Additional collateral