Touchpad as a tablet?

Ok folks...there's something I wanted to clear up. As some of you know, I got my laptop around a month and a half ago. A friend in school also bought one around a month ago.

Now he was asking me if it's possible to use the touchpad as a tablet, using some kind of stylus for the purpose. What he means is: is it possible to write on the touchpad using a stylus of such that the touchpad recognizes the input?

Both of us have Synaptics touchpads, and I don't think it's possible to do any such thing. But I just wanted to make sure from you folks. Any comments on the matter? Do you think it can be done somehow?
Not being an expert on touchpads I'd say no. I believe they are too small and have too low resolution. But I'm not an expert. :)


hardware monkey
i don't think it's a matter of resolution. i've used a synaptics touchpad on an inspiron 8100 and when it can detect your moving the cursor one pixel on a 1600x1200 screen, that's pretty sensitive. more than enough to recognize handwritten text.

but i really have no idea if there's any program out there that changes the role of the toughpad. if there isn't anything, then it's probably not possible. the hardware might be designed so that that kind of touch recognition isn't possible (tracing the movement to complete a figure).
Thanks for the replies, guys.
According to this page (, it says:

Synaptics TouchPad sensors work by using an electrical phenomenon called capacitance. Whenever two electrically conductive objects come near one another without touching, their electric fields interact to form a capacitance. The surface of a TouchPad is a grid of conductive metal wires covered by a plastic insulator, usually gray-painted Mylar®. The human finger is also a good electrical conductor. When you place your finger on a TouchPad, a capacitance forms between your finger and the metal wires in the TouchPad. In Synaptics TouchPads, the "wires" are actually shaped as diamond chains to maximize capacitive contact with your finger. The Mylar® insulator keeps your finger from actually touching the wires and is also textured to help your finger move smoothly across the surface.

The TouchPad's electronics measure the amount of capacitance to each of the wires. By seeing when the capacitance increases, the application specific integrated circuit (ASIC) can tell when your finger is touching. By interpolating the capacitive values seen by the wires, the TouchPad can tell where your finger is to an accuracy of more than 1/1000th of an inch. The sensing electronics are inside Synaptics' patented ASIC on the back side of the TouchPad. The ASIC includes a microprocessor that computes the finger's position and speed and reports them to the main computer in the form of cursor motion. The ASIC also detects when you tap on the pad; it reports taps as simulated mouse button clicks.
Doesn't it seem like it should work with any kind of good electrical conductor then? Maybe a stylus that's made of complete metal that's a good electric conductor?

What do you think? :)


I don't think it would ever work. As your clip said"It is controlled by a ASIC chip" ASIC as you probally know is short for application specific intergrated circuit. The controller [ASIC] is made to do that one thing, so all the software in the world would not help. The only possibility would be to reprogram the ASIC somehow to do what you want it to do. And one more catch, 99% of the ASIC I have dealt with are encrypted!
Yes, but what we want it to do is exactly the same thing as it's doing now. We just want it to be able to track stylus movements instead of finger movements ... no need of any changes in precision or functionality.


That's what needs to be changed, it only tracks the movement so it knows where you are on the desktop, the only command it sends is the click on the item you are on. If you could reprogram the ASIC to record the total movement, then you would have what you want. Another consideration is if the ASIC even has enough KB to do this.
There is a little utility on the site called Synaptics Sketch that allows me to draw using my finger on the touchpad. The "pen" moves as my finger moves along the touchpad, so it does seem like it's recording total movement. Any chance some other material could be used to produce the same effect as the finger (since the finger isn't as easy to control as a stylus, for example)?

Is there more to it than just electrical conductivity?


I will try to explain this a little easier, the asic is probally a 16kb chip. As you move your finger it writes to the next memory cell and clears a previous one. A good example would be to open excel, fill in the boxes as you wish to make a basic outline of a shape. Then hit close and when it asks you to save say no. Now go back to excel and try to open your outline of a picture,guess what? It's not there. This is the problem with the touchpad.


You posted while I was typing, if you can do that, then there is a small chance that modifing their software could work if you can find the code and also find a way to save it. I would be interested in finding a way to do this. Let me look into it a little more, I have a old dell laptop here with that touchpad. If the ASIC is not encrypted, there is a chance of finding a way to save it.
From another Synaptics document:

If the capPen capability bit is set, then a W value of 2 indicates that the pad is currently
sensing a pen, not a finger. An object on the pad surface is considered a “finger” if it
forms a significant contact area and is electrically attached to ground or to a large
conductive body such as a human body. A “pen” is any other type of object, such as a
non-conductive plastic stylus, that makes contact with the TouchPad surface. (Note that
most Synaptics TouchPad products are unable to sense pens, and thus have capPen = 0;
only certain “pen-input TouchPad” models are able to sense pens as well as fingers.)
Does that mean a conducting stylus-like object (one that's possibly made completely of metal) would be detected as a "finger" as well? If so, that's all we would need, right?


hardware monkey
they way i see it, the touchpad chip is sending signals just like a mouse. the rest of the computer thinks you're using a mouse. so when you move your finger across the pad, it thinks you're dragging hte mouse... and when you pick your finger up? the curser is still there... it thinks the mouse is static.

my point is that the hardware would have to able to report when there is nothing touching the pad (after you finish a letter)... which it simply might not be programmed to do.


Tarus is right, not programed to do. And to find a interface that could program it to work would be fruitless, because if you could find it, the ASIC would be to small to handle it.


By the way, how many posts does it take to get past the beginner thing? I want one of those title things like ntfs loser or wannabe type things!
Wow Comptech ... you've been a member for a real long time. :)
Back to the topic: I guess I have to drop the idea then. As I said, I didn't expect it to be possible anyways.

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