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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 a solution using BJT).

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

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!

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  • \$\begingroup\$ Perhaps give each of the four lines its own driver? That way it's the order of activation that determines which axis you're measuring. One independent driver for "LL", one for "LR" one for "RT" etc. \$\endgroup\$ – Sam Feb 22 '17 at 22:12
  • \$\begingroup\$ You effectively need to have an H-bridge. \$\endgroup\$ – pjc50 Feb 22 '17 at 22:32
  • \$\begingroup\$ @Sam thank you for your reply! I think that could be my way out, I have more than enough digital outputs available :) I still have so much to learn about electronics hehe \$\endgroup\$ – R_Est Feb 23 '17 at 0:34
  • \$\begingroup\$ @pjc50 thank you for your reply! Wouldn't an H bridge connect my terminal pairs diagonally? My intention was to connect both top terminals to V+ and bottom terminals to V- or the right pair to V+ and left pair to V-. \$\endgroup\$ – R_Est Feb 23 '17 at 0:37

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