STMPE610 SPI

Github Repo	C Header	C source	JS source
mongoose-os-libs/stmpe610-spi	mgos_stmpe610.h

Mongoose native SPI driver for STMP610E

Introduction

STMPE610 is a chip that drives a resistive touchscreen. It measures pressure on a glass plate which has an X and Y resistor samples the pressure put on the screen (typically by pressing it).

API

This driver initializes the chip and allows the user to register a callback, which will be called each time the driver senses a touch (TOUCH_DOWN) or a release (TOUCH_UP). The callback function will be given the X and Y coordinates, together with an average pressure (Z). For TOUCH_DOWN events, the length field is set to 1. For TOUCH_UP events, the length field is set to the amount of samples read, between 1 and 128.

The X and Y coordinates as read by the screen are between [0..4095), so a mapping function is applied by mgos_stmpe610_set_dimensions(). For screens that are rotated, mgos_stmpe610_set_rotation() sets the mapping function to return them in the correct orientation.

Details

The chip uses an interrupt pin to signal the micro controller that it has something to say. The driver sets up a GPIO pin with a pullup, which the chip pulls to ground to initiate the interrupt. Mongoose OS will receive this and issue a software callback (so no hardware interrupts are used), and the driver will clear interrupts on the STMPE610 after the user supplied handler is called.

Users can query the driver to see if the chip is currently registering a touch by calling mgos_stmpe610_is_touching() which will return true if the user is currently touching the screen.

If the user touches the screen very briefly (only one sample cycle of the driver), the callback will be called with TOUCH_DOWN, but no TOUCH_UP event will be generated. To work around this, the driver sets a 100ms timer upon TOUCH_DOWN, and if the screen is not being touched when the timer expires, a gratuitous TOUCH_UP event is sent with length set to 1.

Example Application

mos.yml

The driver uses the Mongoose native SPI driver. It is configured by setting up the MOSI, MISO, SCLK pins and assinging one of the three available CS positions, in this example (which was taken from the Huzzah32 ESP32 microcontroller), we are going to use CS0:

config_schema:
  - ["spi.enable", true]
  - ["spi.cs0_gpio", 32]      # The STMPE610 CS pin
  - ["spi.cs1_gpio", -1]
  - ["spi.cs2_gpio", -1]
  - ["spi.mosi_gpio", 18]
  - ["spi.miso_gpio", 19]
  - ["spi.sclk_gpio", 5]
  - ["stmpe610.irq_pin", 23]
  - ["stmpe610.cs_index", 0]  # Use spi.cs0_gpio

Application

#include "mgos.h"
#include "mgos_stmpe610.h"

static void touch_handler(struct mgos_stmpe610_event_data *ed) {
  if (!ed) return;

  LOG(LL_INFO, ("Touch %s at (%d,%d) pressure=%d, length=%d", 
      ed->direction==TOUCH_UP?"UP":"DOWN", ed->x, ed->y, ed->z, ed->length));
}

enum mgos_app_init_result mgos_app_init(void) {
  mgos_stmpe610_set_handler(touch_handler);
  mgos_stmpe610_set_rotation(STMPE610_LANDSCAPE);
  mgos_stmpe610_set_dimensions(320, 240);

  return MGOS_APP_INIT_SUCCESS;
}

Disclaimer

This project is not an official Google project. It is not supported by Google and Google specifically disclaims all warranties as to its quality, merchantability, or fitness for a particular purpose.

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This is a library for the Adafruit STMPE610 Resistive touch screen controller breakout ----> http://www.adafruit.com/products/1571

Check out the links above for our tutorials and wiring diagrams These breakouts use SPI or I2C to communicate

Adafruit invests time and resources providing this open source code, please support Adafruit and open-source hardware by purchasing products from Adafruit!

Written by Limor Fried/Ladyada for Adafruit Industries. MIT license, all text above must be included in any redistribution

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/* Adapted for native Mongoose by Pim van Pelt pim@google.com */

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