Thanks to an extended road trip (6000 miles) and receiving pieces for another project in the mail (hello dAISy), I'm a bit late with starting my ESI project log. But here we go.
My project is to detect touch patterns on a resistive touchscreen, e.g. to wake up or unlock a device.
My idea is inspired by figure 28-19 on page 772 of the MSP430FR69xx User's Guide:
The picture reminds me of the circuit for resistive touchscreens:
I plan to approach the project in 3 stages of incremental functionality but also difficulty:
- Detecting touch while ignoring touch location. This should be pretty straight forward use of AFE, TSM and PPU.
- Detecting touch in a specific quadrant of the touchscreen. As the ESI does not have an ADC but only a comparator, detecting the location will have to rely one a binary search algorithm: A measured voltage indicates whether touch happened above or below (and left or right) of a specific point. This will require more complex use of the TSM, maybe even invoking the PSM.
- Detecting a pattern of touch events by the means of a more complex state machine. Besides unknowns about the flexibility of the PSM, I also expect challenges with debouncing touch events.
All the required hardware sits on my desk, so blame any delays on procrastination.