> For the complete documentation index, see [llms.txt](https://veriny.gitbook.io/berkeley/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://veriny.gitbook.io/berkeley/eecs16b/resistive-touchscreen.md).

# 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](https://2947382171-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M6XPH5Qvmbnhx_A2DDH%2F-MJZimuSCQCjbjhFqc6n%2F-MJZjwQPeVOXXXG2Igyx%2FScreen%20Shot%202020-10-13%20at%206.35.47%20PM.png?alt=media\&token=0a75abb0-30a1-4db5-84b2-6f4b643636f2)

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](https://2947382171-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M6XPH5Qvmbnhx_A2DDH%2F-MJZlsUpHwT0e9ug6mjR%2F-MJZpsDClBcQ2vOsijkW%2FScreen%20Shot%202020-10-13%20at%207.01.15%20PM.png?alt=media\&token=12cfa7e4-28ed-4cc1-a4a4-8f7fa205b5d0)

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.