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Capacitive Touch Tutorial from James Lewis - Bald Engineer

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A Capacitive Touch Tutorial

Bald Engineer's VCP Profile  |  Online Learning

 

 

 

Prepare to drink from the firehose!  James opens this video with:

"Push buttons do not work without pull-up or pull-down resistors."

 

But what if you what a button without a physical button?

If you need a brush-up on Pull-up resistors,

check out this AddOhms Tutorial (also done by James).

link to here

In this video you'll learn about capacitors.

Capacitors are, at their most basic, two conductive electrode plates separated by a non-conductive dielectric.

 

An electric field forms between the plates. Different dielectric materials change how much charge can be stored in that field.

 

image

 

A dielectric (or dielectric material) is an electrical insulator that can be polarized by an applied electric field.

In this video you'll learn about:

  • the variables to consider in defining capacitance
  • the equation for defining capacitance
  • how to measure capacitance in a circuit
  • and what is different about capacitance when designing with capacitive touch.

 

James rounds out the video with a review of the TI CapTIvate Dev KitTI CapTIvate Dev Kit - which TI sent him to review.

 

Have more questions on capacitance or the Texas Instruments kit?  Ask them in the comments below!

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  • Nice, enthusiastic tutorial.

    An electric field forms between the plates. Different dielectric materials change how much charge can be stored in that field.

    How does charge get stored in the field between the plates? Don't the electrons put up a bit of a fight if you try and take away their charge?

  • in reply to jc2048

      wrote:

     

    Nice, enthusiastic tutorial.

    An electric field forms between the plates. Different dielectric materials change how much charge can be stored in that field.

    How does charge get stored in the field between the plates? Don't the electrons put up a bit of a fight if you try and take away their charge?

     

    Yes, if you take away their charge, they become a 14-year old emo kid with no identity. image

     

    Saying "charge build up" is almost the same as saying "electron build up."

     

    There's a subtle difference between electrons and electric charge that trip up many people. Most people understand that a conductor allows electric current to flow through it while an insulator does not. Dielectrics are insulators (at least, by definition.) Here's the thing to remember though, electrons move through insulators, and dielectrics, all the time. Electrons are not mated to a specific nucleus. They are swarming around in a cloud-like fashion. This movement effectively means electrons can move through an insulator or dielectric, but the net charge does not change.

     

    In the presence of an electric field (aka voltage), electrons will move through a conductor carrying their charge with them. That is the basis of electric current. When they run into an insulator or dielectric, the charge gets stopped. The electron might keep moving as part of the cloud, but the electric charge does not move with it. The number of electrons, or negative charge, that can build up depends on the dielectric strength of the material. ("Dielectric" is how much of an electric field can the material transmit without conducting electric current.) It comes down to how many positive nuclei are available to attract negative charges? Electric fields will affect how those positive nuclei react, which is how we get capacitors.

     

    I like to use charge because "electrons build up" make it sound like the electrons physically stopped moving. They didn't. They're still swarming around. However, the net number of electrons doesn't change.

Comment
  • in reply to jc2048

      wrote:

     

    Nice, enthusiastic tutorial.

    An electric field forms between the plates. Different dielectric materials change how much charge can be stored in that field.

    How does charge get stored in the field between the plates? Don't the electrons put up a bit of a fight if you try and take away their charge?

     

    Yes, if you take away their charge, they become a 14-year old emo kid with no identity. image

     

    Saying "charge build up" is almost the same as saying "electron build up."

     

    There's a subtle difference between electrons and electric charge that trip up many people. Most people understand that a conductor allows electric current to flow through it while an insulator does not. Dielectrics are insulators (at least, by definition.) Here's the thing to remember though, electrons move through insulators, and dielectrics, all the time. Electrons are not mated to a specific nucleus. They are swarming around in a cloud-like fashion. This movement effectively means electrons can move through an insulator or dielectric, but the net charge does not change.

     

    In the presence of an electric field (aka voltage), electrons will move through a conductor carrying their charge with them. That is the basis of electric current. When they run into an insulator or dielectric, the charge gets stopped. The electron might keep moving as part of the cloud, but the electric charge does not move with it. The number of electrons, or negative charge, that can build up depends on the dielectric strength of the material. ("Dielectric" is how much of an electric field can the material transmit without conducting electric current.) It comes down to how many positive nuclei are available to attract negative charges? Electric fields will affect how those positive nuclei react, which is how we get capacitors.

     

    I like to use charge because "electrons build up" make it sound like the electrons physically stopped moving. They didn't. They're still swarming around. However, the net number of electrons doesn't change.

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