Thankyou gues best i liked all mdel ac ex interseted

Wow, I am blown away. Such care for editing and animation, so simply explained, from a small channel. Thank you, I will use it in my current project!

I'm happy the video is useful.

Much appreciated! Thank you

Thank you. I'm flattered

The signal goes to the smaller plate. If the touch electrode is 1m^2, and the ground plane is smaller, a signal is produced when touching the ground plane (and NOT the electrode). If the ground plane is much bigger than the 1m^2, then the signal produced by touching the electrode will still be small, because the human body is well coupled to the electrode and ground plane to begin with, and moving the finger tip does not change in capacitor's geometry very much so the signal will still be very small.

Iqs127d from Azoteq

To assume the the other plate is virtual ground means the ground plane is very big. To increase the sensitivity of the sensing plate, try to avoid ground plane directly underneath the sensing plate. This is to reduce the baseline capacitance, so that the change in capacitance is higher in terms of percentage.

The ground is not just the pcb ground, but includes the battery ground or earth from the mains. If the battery is big, or the emulator has connection to PC ground,, or the DC adaptor is coupled to the earth, then the total ground is big, and the sensitivity is on the touch pad. The sensitivity is shifted to the touch pad when the device is powered by small batteries.

How big is the plate? When you said 40cm above the ground, is that the electrical ground plane or ground we step on? Using one large plate will not work, because the working principle is that 2 plates sense the external object. The smaller plate has a higher sensitivity and the bigger plate has a lower sensitivity. The large plate you intend to use as the electrode will work against your intention. I demonstrated this surprising and unintuitive result in my other video "teardown of miband3". The equivalent circuit is shown in kzfaq.info/get/bejne/kK6qlLmrvqu-kqs.html. The circuit is simple, but it does predict bigger plate having smaller sensitivity and visi versa. The parallel plate model is incomplete. I hope this helps.

@@SiliconSoup The plate's area is 24cm*24cm.The ground is ground we step on.My intend is to achieve a long proximity distance,e.g. 50cm.This purpose requires the use of larger plates.

@@user-py1il3ic2l Firstly, is your circuit battery powered or AC powered (through DC-adapter)? If you circuit is AC powered, inherently the circuit ground is connected to the earth of the electrical system, so you already have a big ground plane, so together with the 24cm X 24cm electrode, they can sense any big object coming in between them. The object will have to be same or bigger size to make significant change to the capacitance. However, if you have a 24cm x 24cm electrode, and a small circuit ground (if the circuit is battery powered), then the circuit will not work as intended. In fact you will find the sensitivity goes to the circuit ground, the small plate. So what you need to do is to enlarge the circuit ground to an area comparable or larger than 24cm x 24cm. Again, I like to emphasize that the capacitance between the single plate and the object need a good return path back to the circuit for the capacitance to be detected, that the good return path is formed by a much bigger ground plane coupling to the object. If you are dealing of long distance, the signal change can be small, so you need a sensitive capacitive sensing IC. Not all sensing IC have good SNR. I strongly recommend azoteq, because I experimented with it, and it is really good.

When charges are separated, they want to reunite and therefore they have the potential to do work. When the plates lose some potential, then the potential is lower then that of the battery, then charges flow from higher potential (battery) to lower potential (plates). After I made this video, i think a better explanation for the activities is based on the forces, not potential, because potential is a derived property from the force. When the object is polarized, the negative charges on the left side of the object (2:00) attract positive charges into the left plate (by e-field/force), and the positive charges on the right side of the object attract negative charges into the right plate.

Thanks a lot, i really appreciate your quick and detailed answer ;)

This video is about self-capacitive sensor. I have a video to analyse self capacitive sensor using lumped capacitor. I also have other video on mutual or projected capacitive sensor, in the same KZfaq channel. Thanks for watching.

@@SiliconSoup thanks for your explanation. But there's one thing I don't quite understand. In your video, at about 1 minute and 55 seconds, there are two other electrodes in addition to the target object.Shouldn't such a structure be mutually capacitive? I think if it is self-capacitive, there should be only one electrode acting as the sensor, and the object forms a capacitor with it. By the way, could you tell me which paper appears at 2 minutes and 45 seconds of the video?

@@user-py1il3ic2l There is no such thing as a one-plate capacitive sensor, as minimum two plates are needed to make a capacitor, and the object cannot be considered as one plate because it is not electrically connected to the circuit. The touch plate and the ground plane together form the sensor. Many people didn't know about the role of the ground plane in the sensing, and misunderstood that the touch plate is the only plate doing the sensing. This misunderstanding, has resulted in this sensor called the self-capacitive sensor. Strictly speaking, based on my academic knowledge on multi-conductor capacitor, the capacitance being sensed in the circuit is the mutual capacitance (so you are absolutely right), and this type of sensor should be called the mutual capacitive sensor. Another reason it is called the self-capacitive sensor, is from the implementation point of view; the charging of voltage and the sensing of induced charge happen on the same plate. The article is "The method of Moments in Electromagnetics", Massachusetts Institute of Technology, 6.635 lecture notes.

The average power consumption of the sensor IC is the same, whether the object is near or far. Theoretically, in "charge transfer" method of capacitive sensing, object at further distance requires more transfer cycle to trip the sensor, so yes it take more power to sense object at further distance, but really not a consideration in engineering.

@@SiliconSoup thanks so much!! Just for my understanding of the concept

The electrodes that detect the capacitance must be conductive, e.g. copper or ITO (Indium Tin Oxide). The gap between the electrode and the finger must be non-conductive, such as air, acrylic, glass, because electric field can pass through this media. Water, salt-water, aluminium cover are conductive and block the e-field and therefore should not sit in between the electrode and finger. Of course, a little bit of water on the cover will not block the e-field fully, so capacitive sensing is still possible, if the circuit is very sensitive.

@@SiliconSoup Thank you for your kind reply! I was overjoyed this morning. But I still have something that I can't understand. I think I had not been able to convey the meaning of what I'm trying to say. I did not mean that touchscreen could be touched with your hand when the water or the salt covered it. I experimented to see if the touchscreen reacts to the liquids, by putting several kinds of liquids in a non-conductive thin plastic bottle(Vial). The result was that when the liquid was water(or drink containing water such as coffee), glycerin, or ethanol, touch was possible but the screen did not work when the liquid was oil like gasoline or cooking oil. When tested in solid form, I I was possible to touch the screen with metal objects(such as locks, aluminum foil, even copper wire inside charger wires) , PE(on of the plastic) and solid salt in thin plastic containers, and in the case of most of non-conductive materials, such as solid sugar, plastic(except PE), cotton, rubber, paper and Calcium carbonate, touch was impossible. What I am wondering is, what is the criteria for the substances which makes the change of electric field?Another thing I am wondering is if it works by moving of the electrons from screen to substance changing the electric field of the screen, why does it work even when there is a non-conductive material between the finger and screen?I do not know if it was delivered properly, but I would really appreciate it if you answered it again!

The criteria for the substances to interact with the electrode is the conductivity. Conductive material like water, human body can interact with the touch screen, but plastic cannot. But being conductive is not enough, the conductor (e.g. human) must be able to couple to the sensing circuit by two ends, one end is the finger couple to the touch electrode by the small gap, and the other end the human body (or palm) to the ground plane by big surface area (watch 5:00). If you put a coin on your phone, it will not trigger because its like a finger without a body. The electrons cannot move from the screen/electrode to the substance. The physics is explained in 2:01. The electrode polarize the substance. The polarized substance in return attracts more electrons to the electrode, from the voltage source. BTW, the video is about surface capacitive sensor. Touch screen uses projected/mutual capacitive sensor. The physics behind surface and projected sensors are different, and the response is directly opposite. For example, a touch on surface capacitive sensor increases the capacitance, whereas a touch on project/mutual capacitance decreases the capacitance. I have another video on mutual capacitive sensor (kzfaq.info/get/bejne/nd58rcqWzrC1knk.html). The video here is for surface capacitive sensor, and not directly applicable to touch screen (projected type), precisely speaking.

It is a demo set that uses very sensitive capacitive sensors to control the RGB LEDs.

charges move from higher potential to lower potential. As more charges built up across the plates, the potential difference increases until it is the same as the voltage source and so a new equilibrium is established.

Pebble Soup Nice one

Yes, we can always discuss about this topic. I am not sure how to give you my gmail address without publicly reveal it here. We can discuss here too.

@@SiliconSoup Hey, I'm sorry if what I described was too long. Just email me on this id: cryptowriters@gmail.com. I don't use it much, and I'll delete the comment once you message me. Thanks.

+Bo Cheng Mains wiring refers to 110V AC or 230V AC lines. Capacitive sensors in appliances are much more sensitive than those in handheld devices. The neutral wires increase the "ground plane" area, so it not only increase the sensitivity but also shift the sensitivity to the touch buttons.

+Pebble Soup Thanks for the explanation. Another question: I came across an issue that the trace where wiring the button to the controller also gets the sensitivity, in other word, the trace are also acting like switches. How do I decrease the sensitivity on the trace? (I tried added ground plane around it, shorten the spacing but it still didn't work well)

+Bo Cheng use the thinnest trace allowed by the PCB fabrication. This is to make the trace area much smaller than the touch pad area. If the touch pad is on the top side of the PCB, put the trace on the bottom side.

+Michelle Ang Capacitive sensor can be used for measuring liquid level, but I am not sure whether it is actually used for aircraft fuel.

i saw the same person with same comment in some other links too!

for self-capacitive sensor, the baseline capacitance should be small, so that the change of capacitance in percentage is big when the finger moves in. Any unwanted capacitance adding to the baseline is the parasitic capacitance. For example, a signal line underneath the sensing electrode is a parasitic capacitance. In fact, all metals in the circuit will form capacitance with the sensing electrode and are parasitic capacitance too. But due the far distance, the impact is not as big and signal lines underneath.

if you model your body as a perfect conductor, then when your finger moves relative to the touch sensor, charges on your body redistribute, but there is no gain or loss in energy, because no energy is required to move charges on a perfect conductor. If body resistance is taken into consideration, when your finger is near the sensor and your body is polarized, you gain energy (from the supply of the sensor). But when your finger moves away from the sensor, the polarized charges reunite through the body resistance and release energy through heat. This is academic fun :)