Capacitance measurement (high speed)

Thread Starter

goutham1995

Joined Feb 18, 2018
94
I need to measure pressure being exerted on multiple areas of a disc being hit by hand ( maybe at a speed of playing bongo). Is it possible to do so using capacitance measurement using capacitive touch sensors? I've seen apps on iPhone and android which emulate a drum and is capable of producing sound at the speed at which I hit so i think it should be possible since mobile phones too use capacitive touch sensors
 

Analog Ground

Joined Apr 24, 2019
365
The answer is yes. For example, a microcontroller I am currently using has a "Touch Sensitive Interface" which uses capacitive sensing. The interface can scan 16 areas (capacitors) at over 500 times a second or 8 areas at over 1,000 times a second, etc. The measurement time will depend of the value of the capacitance. However, it can be quite fast.
 

Thread Starter

goutham1995

Joined Feb 18, 2018
94
The answer is yes. For example, a microcontroller I am currently using has a "Touch Sensitive Interface" which uses capacitive sensing. The interface can scan 16 areas (capacitors) at over 500 times a second or 8 areas at over 1,000 times a second, etc. The measurement time will depend of the value of the capacitance. However, it can be quite fast.
Thanks. Which microcontroller are you using? And have you actually scanned them at that rate?
 

Analog Ground

Joined Apr 24, 2019
365
Thanks. Which microcontroller are you using? And have you actually scanned them at that rate?
I am using the NXP KL25 but many other NXP microcontrollers have the TSI module. The TSI chapter in the reference manual has sample rate calculations. I have not run it at high speed but would believe the calculations. There are many other ways to make the measurement. Some use a dedicated IC.
 

Analog Ground

Joined Apr 24, 2019
365
Thanks. But where does it say this?
See post #4. The microcontroller reference manual has an entire chapter on the capacitive sensing interface. How it operates and calculation of the rate of capacitance-to-digital conversion is covered in detail. The reference manual is available on the NXP web site. It is 900 pages long. So, I cannot post it. The conversion time is not simply a value in a data sheet. It depends on settings in the device, resolution of the measurement and the range of capacitance to be measured. Equations for the conversion time are in the manual.

This sort of specification is typical for capacitance-to-digital converters. So, some work is required. Also, how you will connect to the capacitance to be measured is very important. Are the capacitors floating and independent of each other or are they connected together with one common electrode which is typically grounded? How long is the cable to connect the converter to the capacitances? What is the capacitance of the cable? The idea I am trying to convey is capacitance measurement is more complicated then resistance measurement.

It is impossible to recommend a specific converter without knowing a lot more about your requirements. My post is just one opinion that the answer to your question is "yes".
 

Thread Starter

goutham1995

Joined Feb 18, 2018
94
See post #4. The microcontroller reference manual has an entire chapter on the capacitive sensing interface. How it operates and calculation of the rate of capacitance-to-digital conversion is covered in detail. The reference manual is available on the NXP web site. It is 900 pages long. So, I cannot post it. The conversion time is not simply a value in a data sheet. It depends on settings in the device, resolution of the measurement and the range of capacitance to be measured. Equations for the conversion time are in the manual.

This sort of specification is typical for capacitance-to-digital converters. So, some work is required. Also, how you will connect to the capacitance to be measured is very important. Are the capacitors floating and independent of each other or are they connected together with one common electrode which is typically grounded? How long is the cable to connect the converter to the capacitances? What is the capacitance of the cable? The idea I am trying to convey is capacitance measurement is more complicated then resistance measurement.

It is impossible to recommend a specific converter without knowing a lot more about your requirements. My post is just one opinion that the answer to your question is "yes".
Thanks
 
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