[NTLK] Why are pen alignments needed?

Andrei Chichak newton at chichak.ca
Sat Dec 8 19:30:56 EST 2018

You’re comparing a system that STOPPED being made 20 years ago to things that are about 10 years old and are in their 9th generation?

The newton uses a touch screen that is effectively two sheets of resistive material where you pass a voltage across them, and the two voltages vary depending on where your finger/stylus hits.

Then the electronics of the newton turns these voltages into numbers that represent the position by using a device called an analog to digital converter (ADC).

A few things to know, everything in electronics is a temperature sensor. The ones known as temperature sensors are special resistors that vary with temperature in a predictable way. But every resistor is a temperature sensor, some are just better than others. So as the temperature of your screen changes, so does the resistance so screen positions will wander.

Next, since there are two active sheets in the newton digitizer they use little bumps to keep them apart, because if they come into contact with each other, it gets picked up as a bit of a touch.

Next, the resistor XY digitizer can only pick up one touch point at a time. If you touch the screen with two fingernails, it will give you a position in the middle of the two. The centroid.

Now, assume that you smack your screen with the stylus and it makes a bit of a dent. Not enough to make a complete touch, just enough to bias the resistive panels. Now when you place your stylus somewhere else, you get the centroid of the new stylus touch, shifted slightly towards your dent.

One of the models was miserable for getting hand goo under the bezel. This would screw up the alignment toward the point in the bezel that is pressing on the digitizer. You could fix it by running a business card between the digitizer and the bezel. Sometimes the bezel would just warp and press on the digitizer, removing the screen and scraping the bezel to remove some material helped.

So why do you have to do alignments? To counteract the non-stylus presses on the digitizer.

Why don’t you have to do this on a modern mobile device? Because they use a capacitive digitizer that works in a completely different manner, it doesn’t squish, and has had 20 years of development to bring it to the point that it is today. If anybody brought out a mobile device that used resistive touch today, they would be laughed out of the market. 

What can you do to prevent a newton from needing alignment? Get an iPhone, most of the good points of a newton are there without the bad points.


> On 2018-December-05, at 09:05, Doug <ispinn at gmail.com> wrote:
> AFAIK, no current mobile devices need alignment.
> So, can someone explain why pen alignments were necessary on the Newton?
> What things were going out of alignment, what caused it, and what about the
> Newt prevented its having permanent alignment?
> Doug
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