Resistive Touchscreen

Adapted from EECS16A Note 12, 13, 14

1D Model

We can simplify the touchscreen to a 1D structure in order to gain a better understanding of how it works.

Credit: EECS16A Note 12

We want to calculate the $L_{touch}$ in order to find the position of the touchpoint. As we know, it, $I = \frac{dQ}{dt}$ , where $Q$ and $I$ are charge and current respectively. We measure current in amps, which amounts to one coulomb per second.

The resistance of a conductive material is given by the equation $R = \rho \frac{L}{A}$ , where rho is the resistivity (a number unique to each material) L is the length and A is the cross-sectional area.

Credit: EECS16A Note 12

As you can see, you write the resistances of the two resistors in terms of the resistivity, which brings length into the equation, allowing you to solve for $L_{touch}$ using node voltage analysis. Simply solve for $u_{mid}$ in terms of $R_1$ and $R_2$, and then you can plug the resistivities in.