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Example_Touchpads/I2C_Touchpad.ino

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+/* Copyright 2021 Frank Adams
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+       http://www.apache.org/licenses/LICENSE-2.0
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+// This software implements an I2C Touchpad Controller using a Teensy 3.2 
+// It assumes the TP is at I2C address 0x24
+// Register 0 is the pointer register used to access all other registers
+// Register 1 is the button register. 0x00=no buttons, 0x03=left button, 0x04=right button
+// Register 2 function unknown - not used
+// Register 3 is the X delta movement 8 bit 2's complement value. Left to right gives positive values
+// Register 4 is the Y delta movement 8 bit 2's complement value. Top to bottom gives positive values
+// Register 5 function unknown - not used
+// Register 6 is the touch sensor. 0x00=no touch, 0x0f=touch - The code below does not use this register
+//
+// Release Date: August 3, 2021
+//
+#include <Wire.h> // used for i2c bus to touchpad
+//
+// define the pins on the Teensy used for the touchpad I2C bus
+#define TP_DATA 14 // Touchpad i2c data signal 
+#define TP_CLK 15  // Touchpad i2c clock signal 
+
+//
+//----------------------------------Setup before main loop-------------------------------------------
+//
+void setup() {
+Wire.begin(); // i2c for touchpad
+}
+// declare and initialize touchpad variables  
+char buttonreg; // touchpad left and right buttons read from register #1. Left button is bit 0 and 1, right button is bit 2
+char xreg; // touchpad x movement from register #3. 2's complement, left to right movement gives positive value. 
+char yreg; // touchpad y movement from register #4. 2's complement, top to bottom movement gives positive value.
+boolean left_button = 0; // Active high, on/off variable for left button 
+boolean right_button = 0; // Active high, on/off variable for right button 
+boolean old_left_button = 0; // Active high, on/off variable for left button status from the previous polling cycle
+boolean old_right_button = 0; // Active high, on/off variable for right button status from the previous polling cycle
+boolean button_change = 0; // Active high, shows when a touchpad left or right button has changed since the last polling cycle
+//
+//---------------------------------Main Loop---------------------------------------------
+//
+void loop() {   
+// poll the touchpad for new movement or button data 
+//
+  Wire.beginTransmission(0x24); // Load the TP register pointer 
+  Wire.write(0x01);             // so it points to register 1
+  Wire.endTransmission();       // 
+  Wire.requestFrom(0x24, 4); // Read 4 bytes from the TP starting at register 1
+    
+  buttonreg = Wire.read(); // read the button status bits in register 1
+  Wire.read(); // read and throw away byte from unused register 2
+  xreg = Wire.read(); // read the X value from register 3
+  yreg = Wire.read(); // read the Y value from register 4    
+// send the x and y data back via usb if either one is non-zero
+  if ((xreg != 0x00) || (yreg != 0x00)) {
+    Mouse.move(xreg,yreg);
+  }
+//
+// check the left and right bits in the button register from the touchpad
+  if (buttonreg == 0x03) {   // the left button is pushed 
+    left_button = 1;   // set the left button variable
+  }
+  else {   // otherwise clear the left button variable
+    left_button = 0;   
+  }
+  if (buttonreg == 0x04) { // the right button is pushed
+    right_button = 1;   // set the right button variable
+  } 
+  else {   // otherwise clear right button variable
+    right_button = 0;  
+  }
+// Determine if the left or right touchpad buttons have changed since last polling cycle using xor
+  button_change = (left_button ^ old_left_button) | (right_button ^ old_right_button);
+// Don't send button status if there's no change since last time. 
+  if (button_change){
+    Mouse.set_buttons(left_button, 0, right_button); // send left, middle, and right button status
+  }
+  old_left_button = left_button; // remember button status for next polling cycle
+  old_right_button = right_button;
+//
+  delay(25); // This is the polling rate in msec
+// 
+}