Does the negative end of a battery works better than a capacitive stylus because of electric charge?

Question

I have a tablet with a capacitive touchscreen. I bought a wacom bamboo stylus duo which I thought was a good stylus. But the effect is rather disappointing. I get broken lines all over the screen when trying to draw.

I saw some DIY posts suggesting using the negative end of a battery as stylus. It works. And it works better than all my capacitive stylus.

But I wonder how it works? As the outside of the battery should be non-conductive? I tried wrapping it with another piece of paper and I can still use it as stylus. So it seems to me that the negative charge on the battery is doing the work. But then, if I tape the negative end of the battery to my capacitive stylus, it didn't help. Why?

Answer 1

The way cylindrical button-top batteries such as AAA are made, is that they have a steel casing that goes the complete length of the battery and includes the negative terminal, this is all a single piece of steel. At the button top, there's an insulating washer or seal to the positive pole. Since for the lack of electrical connection, no current can flow through the battery, the battery probably does not significantly participate in the capacitive sensing, it's just the casing. By touching any part of the side casing, you are capacitively well-coupled to the negative terminal.

A capacitor is constructed from two conductive surfaces separated by a dielectric, an insulator. No direct current can flow, but high-frequency signal can pass through a capacitor, as the charge on one plate influences the other.

The capacitive sensor is a matrix of vertical and horizontal antennas placed every few mm across the touchscreen between the display and the cover glass - you might be able to see them in just the right lighting. They emit a high frequency signal and measure the current consumed. When there is no object in proximity of the screen, no current can flow. When your finger touches the screen, a chain of capacitors to ground or the environment is formed: the glass or plastic surface of the screen forms a first insulation layer and thus the first capacitor, and your body forms a capacitor to ground or the environment. Let's say you touched a battery casing directly, then it's just the extension of your body. But if you're touching it through the insulating thin layer of plastic that is glued onto the casing, you're simply introducing another capacitor. It is perhaps a matter of luck that the properties of the capacitor introduced still allow it to be effective at the sensing frequency, and even more lucky that it still works through paper - there is naturally also capacitance between the casing and the button top, but you may notice that the button top doesn't work nearly as well. This chain of capacitors to ground allows a small current to flow towards ground and then back as the polarity of the high-frequency signal flips over, and this current is measured by the sensor array.

The capacitive chain however has to go somewhere, to some fixed potential. You couldn't possibly hang a battery or capacitor against a touchscreen in a vacuum and expect it to work.

Answer 2

OK, you asked a bunch of questions.

Lets start with how capacitive touch screens work. Read more here.

Capacitive touch screens work with anything that holds an electrical charge – including human skin. There are two main types of capacitive touch screens – surface and projective. Surface capacitive uses sensors at the corners and a thin evenly distributed film across the surface (as pictured above) whereas projective capacitive uses a grid of rows and columns with a separate chip for sensing.

So, a capacitive touch screens will work with your styles and your finger and many other things, like.... your battery.

This leads to your second question: shouldnt the outside of the battery be non-conductive? To put it simply, a battery HAS to be conductive or it wouldnt be a battery. Now, only the ends are conductive, otherwise the battery would just short out. Since the ends are made out of metal, which can hold a conductive charge... see where I am going? That is why the battery works as a stylus.

So you taped the battery to the end of your stylus and it didnt help. Why? More than likely you "confused" touchscreen. Both the battery and the stylus (which has a conductive material inside it) were interacting with the screen and the chip controlling the touchscreen had issues dealing with the input.

If your stylus isnt working as well as you would like, go to a computer or office supply store, or online of course. They often have replacement styluses for different products that might work for you.

Answer 3

Negative end of a battery doesn't contain negative charges. for example you cannot drain a battery by connecting it's negative end to ground. charge inside a battery is created by a chemical reaction and for the reaction to happen both negative and positive ends of the same battery must be connected with each other.

but somehow what you are asking does make sense. because capacitive touch panels recognises the voltage difference between users finger and the capacitive grid it can recognize a battery as a finger not because of its negative charge because it is charged in the same way as your finger due to its conductive metal casing and it's very short length.

how ever we can make a negatively charged stylus using a capacitor instead of a battery. since capacitors actually store charges between their plates.
you should try the same experiment with the negative leg of a charged capacitor and see if the result are any better.

also i'm not an electronics geek. i apologize before hand if any technical term i used here is wrong.