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AndAway

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  2. x/y touchpad controller

    in Parts Archive

    Posted

    No, You don't have to connect the ground here... You won't get voltages from 0V to 5V, but from something above 0 (on the left you have +5V ane when You press on the farest point to right)  to something under 5V, that's why You need to change the software...

    Take normal pot - when You turn max to left You have a short-circuit between the ground and signal. Turn it max to right - a short-circuit between +5V and signal. With touchpad You'll never have such a short-circuit (but You can match a voltage divider to give You 5V output). Still You need more than 5V for such voltage divider...

  4. x/y touchpad controller

    in Parts Archive

    Posted

    Each of these "2 pads" - the first picture (it is one in fact) has two connectors, one for +vcc and the other to the analog input. You would be able to connect it to the analog in if R=10Kohm, but they are max 1,5 Kohm, so You have to use a voltage divider with an impedance buffer (or play somehow with software).

    So You have 4 pins: two for +vcc and one for x-output and one for y-output.

    Btw. I don't think You should separate those 2 layers...

  5. x/y touchpad controller

    in Parts Archive

    Posted

    Hi List

    As moogah said:

    >For the softpots I was thinking of software that ignores the absolute position and only listens the the change in signal, so that If you slide >up it increments the value, sliding down decrements the value, reguardless of where you touch the pot. 

    I think that this solution is used in laptops. And the soft would be easy (for somebody with basic prog. skills :) ). Also some sensitivity value should be taken into consideration...

    I've made a very simple circuit which changes the output of the pad to values 0-5V but I don't have a place to post it. I have schematics and pcb in the eagle format (my first drawing). If someone is interested i can send it to him.

  10. x/y touchpad controller

    in Parts Archive

    Posted

    It seems that it won't be so easy... In fact You don't get diffrent resistance values for x and y. Peel off the adhesive paper from the pad and You will see why... There are 2 'sheets' of that carbon resistive material placed one over the other, each with 2 connectors on the opposite side. Pressing in some point makes the 2 sheets touch each other.

    When You connect a multimeter, You will get values from "upper-left" connectors and "lower-right" connectors. Connecting one sheet (ex. upper and lower pin) makes the multimeter show 0,5 KOhm - impedance of one 'sheet'.

    When connected pins are lower and left, in this corner You get 0,5KOhm. Diagonal is the line of constant impedance equal 1KOhm. In the upper-right corner of the pad You get 1,5Kohm.

    The other connector behaves simmilar.

    The idea with voltage divider may work, but additional impedance buffer may be needed.

    Any ideas??

  11. x/y touchpad controller

    in Parts Archive

    Posted

    The spectra pad consists of 2 resistors, each of imp about 1KOhm. You can build a simple voltage divider - the only con is that You need more than 5V as the input (my PSU delivers 5 and 12V)

                                       

         Vin--???---------?-----------Vout

                   R1-pad      ?

                                       ?R2

                                       |

                                       |

                                      Gnd

    Vout=Vin[ R2/(R1+R2)]

    Assuming Vin=12V, R1=1K and Vout=5V You get R2=450Ohm

    You will need 2 of those circuits for x and y axis.

    But I'm not sure if this will work (loaded voltage divider - Thevenin's theorem???), waiting to have some spare time to check if it works in practice.

    Andrew

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