How to allow two out of four of the touch screen terminals to be supplied
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  1. #1
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    Default How to allow two out of four of the touch screen terminals to be supplied

    I'm trying to build a controller for a 5 wire resistive touch screen using one microcontroller's digital outputs interfaced with some transistors (currently trying BJT transistor 2sb1647 from kynix: Memory, Flash, IC, integrated circuits ,Electronic Components distributor - Kynix Electronics).

    My objective is to allow two out of four of the touch screen terminals to be supplied simultaneously so I can read a given touch position.

    In order to read a position on the X axis from left to right, where the output voltage Vo would be Vo=V+ (V+ being a positive reference voltage) on the right edge of the screen, I would need to connect RT and RL to V+ and LT and LL to V- (V+ > V-).

    In short, I need a circuit that will work like this:
    - RT, RL = V+ ; LT, LL = V- => X+ - LT, RT = V+ ; LL, RL = V- => Y+

    This should represent what I'm trying to explain:

    LT -------- RT
    |--------|
    |--------|
    LL -------- RL
    I came up with a circuit that works fine with a single axis, but it fails to do what I intend when I insert the second axis control.

    This is the circuit I came up with so far, using two microcontroller outputs: enter image description here

    srg2s.jpg
    The LEDs simulate the touch screen terminals, the switches simulate the microcontroller outputs, which will only be ON one at a time.

    If I replicate the same circuit for the Y axis, all the LEDs will be ON, obviously... I'm struggling to come up with a circuit to disable one of the axis' control circuits in order to let the other be able to work.

    Any ideas or suggestions will be more than welcome.

    Thank you in advance!

  2. #2
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    First, RT is always V+ and LL is always 0volts.

    Now all you need is a single output that switches RL and LT

    You could use that single output to drive RL and LT to opposite values.

    RO goes to the analog input.

    Hope that helps.


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