Testing touch on small SPI epaper displays

Our now IDF ver. 5 compatible touch component FT6X36 is ready to be tested.

There are two affordable models that I would like to cover in this post. First one is the 400×300 FT6336 from Good Display, we can see this one in action (2nd video, 1st had still wrong Waveform)

I2C touch interface Focal Tech. Pin-out follows:
1 GND
2 VDD -> 3.3V only, not 5V!
3 RST (Not used in this component)
4 INT
5 SDA
6 SCL

It’s important to know that each different model uses a different pinup in the 6 pin FPC cable, so if you had the great idea to make an universal adapter, you will fail doing it (Guess who tried?)
Please note also that I do not use GoodDisplay touch adapter for this since I do not like the fact that you can use it only for touch or for SPI but not both, so I choose to use a simple 6 pin FPC adapter that you can find cheap in Aliexpress.

Note there is a small gotcha with this ones! Sometimes the FPC is bottom-contact only so make sure to plug it with the contacts facing down (Disregard this if it has double sided contacts)
Also we are using a very raw touch interface to MCU connection there are some technical things to keep in mind:

1. I2C is a bidirectional connection and needs pull-up resistors to 3.3V in both SDA and SCL lines (4.7K or even 6K Ω will work)
2. INT pin goes low when there is an event to read via I2C. Same as last case, you should not leave this pin floating and add also a pullup to 3.3V.

The 2.7″ smaller brother

The smaller 2.7″ has also an optional touch screen. This model called Gdey027T91T with 264*176 pixels resolution seems to be at the moment out of stock, but you can get the touch separately, and just stick it with care in the top of the epaper display.

In the video you can see how fast partial update works in this model, compared with my 4.2″ version
1 GND
2 INT
3 RST (Not used in this component)
4 VDD
5 SCL
6 SDA

Also if you want to use Espressif IDF framework to handle touch events plus epaper component with GFX, we highly recommend to try Cale-idf
Cale is a component that is already 2 years in development and has the most common epapers from Goodisplay / Waveshare, including this two touch models. It also has the interesting fact, and sometimes important, if you design something that is able to rotate screen of adapting touch to this rotation. Only on certain classes like the 2.7″ since we are no-one requested yet to add this feature to the 4.2″ display class.
On our example demo-keyboard.cpp on cale component you can clearly see how this is implemented:

// Include touch plus the right class for your display
#include "FT6X36.h"
#include "goodisplay/touch/gdey027T91T.h"

// INTGPIO is touch interrupt, goes low when it detects a touch, which coordinates are read by I2C
// Use an RTC IO if you need to wake-up with touch!
FT6X36 ts(CONFIG_TOUCH_INT);
EpdSpi io;
// At this moment we insert touch into the display class!
Gdey027T91T display(io, ts);

uint8_t display_rotation = 3; // 1 or 3: Landscape mode
int t_counter = 0;

// This callback function will be fired on each touch event
void touchEvent(TPoint p, TEvent e)
{
    ++t_counter;
    printf("X: %d Y: %d count:%d Ev:%d\n", p.x, p.y, t_counter, int(e));
}

// Entry point of our Firmware
void app_main()
{
   // Initialize display and SPI
   display.init(false);
   // When using the ClassT integrated with touch then rotating this
   // rotates touch X,Y coordinates too.
   display.setRotation(display_rotation);
   display.registerTouchHandler(touchEvent);
  
   // You could launch this also in a FreeRTOS task
   for (;;) {
     display.touchLoop();
   }
}