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does anyone know how an 'active' stylus works? I know it involves magnets somehow- Answered

I bought a hybrid tablet, and playing games on a touch screen is COOL.  However, i want to make an ergonomic stylus; my hand cramps up too badly when i play for long periods.  I had an idea to buy a wacom stylus and modifying it, and I'm trying to figure out more about how it works before I start.  (lol) making stuff is cool; but i would prefer to not go into it blind.


Generally, it's capacitive, and inductive.

There are 2 layers to the sensor, on one layer the strips are all connected horizontally, on another layer vertically. Each strip acts as an antenna, sending out a little bit of radio energy when its turned on.
Each strip is also turned on only one at a time.

The stylus has a coil and possibly a microcontroller to send back signals (like the contact click or rightclick button)

now what happens is really smart. It pulses row 1, and if the pen is in range, it gets power and replies 'hey I'm here'. After row 1 turns off, it becomes a listener antenna for that reply. Same thing happens underneath, column 1 pulses and listens. By cycling the rows and columns VERY quickly and averaging the results (how strong the signal was on each row and column) its possible to determine the xy coordinates of the stylus.

As for building your own, you need it to reverse engineer whatever is in the original.
BEST BET is to buy a replacement, and add something like Sugru to the grip to make it more hand-friendly.

+1. Best bet is to use their circuitry, and the easiest way to do that is to come up with something which simply holds their stilus.

love your name :)

I dunno if the question i asked frollard posts to you too; and it looks like you've already answered the last couple questions on these things.
I'm probably going to go the sugru option since these things are pricey *wince* but would you know how these things work? I specifically have a fujitsu t4220, which I THINK is a wacom, does it basically use RFID-type tech?

Frollard's description is about right.

Old-style electromagnetic: Tablet is a grid of wires, pen/puck is a pickup coil. Pulse wires in turn until the pickup reports a strong signal, meaning the two are close together. Do that both vertically and horizontally, and you have the location.

New-style electromagnetic: : I'm not sure whether the Wacoms do that and have an RF transmitter to signal when they've gotten the pulse, or if they reverse the process and have the pen be the transmitter, scanning input from each of the grid wires to see which are responding. There's probably a patent that will answer that question, if you want to make the effort to do some searching.

Touch is a different mechanism; there are several different technologies. When I was designing touch-screen systems, we were mostly using capacitive touchscreens, but there are other designs (straingauge, for example).

thanks for the awsome quick response! Maybe I'm using the wrong term... my stylus doesn't appear to have any sort of battery- but it DOES have a 'writing' tip, and 'erasing' tip, and a left/right (top/bottom) 'mouse' keys. Do you think it's rfid controlled?

Ha, I apologize for being a flake, more specifically I have a Fujitsu t4220- according to various google sources, the stylus is very possibly made by wacom.

*sigh* Alas, at $30 a pop; I might take the sugru option instead of the cooler reverse engineer method.
(lol) Maybe I'll get lucky on ebay.

and 30/each plus the description of having buttons and 2 different tips tells me its got to have 'intelligent' guts, not just a resistive or capacitive touch surface, so rfid + grid sensing it is.

Yes, it has no battery.

RFID technology uses magnetic coupling to transmit enough energy to the pen's smarts to let the pen respond "I'm here, and I'm clicking this button", hundreds of times per second.