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Example_Touchpads/Touchpad_3p2.ino

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+// This software is in the public domain
+// It interfaces the Teensy 3.2 with a PS/2 touchpad found in a laptop.
+// The PS/2 code was originally from https://playground.arduino.cc/uploads/ComponentLib/mouse.txt
+// but the interface to the PC was changed from RS232 serial to USB using the PJRC Mouse functions. 
+// A watchdog timer was also added to the "while loops" so the code doesn't hang if the touchpad hiccups.
+//
+// This code has been tested on the touchpad from an HP Pavilion DV9000
+// Touchpad part number 920-000702-04 Rev A
+// The test points on the touchpad were wired to a Teensy 3.2 as follows:
+// T22 = 5V wired to the Teensy Vin pin
+// T23 = Gnd wired to the Teensy Ground pin   It's hard to solder to T23 so I soldered to a bypass cap gnd pad.1 
+// T10 = Clock wired to the Teensy I/O 14 pin
+// T11 = Data wired to the Teensy I/O 15 pin
+//
+// Clock and Data measure open to the 5 volt pin, indicating no pull up resistors but,
+// Clock and Data both measure 5 volts when the touchpad is powered, indicating active pullups are in 
+// the touchpad blob top chip.
+// The ps/2 signals are at 5 volts from the touchpad to the Teensy which is 5 volt tolerant.
+// The ps/2 signals are at 3.3 volts from the Teensy to the touchpad which is enough to be a logic high.
+//
+// Revision History
+// Initial Release Oct 16, 2018
+//
+// The touchpad ps/2 data and clock lines are connected to the following Teensy I/O pins
+#define MDATA 15
+#define MCLK 14
+//
+// Declare variable that will be used by functions
+boolean touchpad_error = LOW; // sent high when touch pad routine times out
+//
+// Function to float a pin and let the pull-up or Touchpad determine the logic level
+void go_z(int pin)  
+{
+  pinMode(pin, INPUT); // make the pin an input so it floats
+  digitalWrite(pin, HIGH);
+}
+// function to drive a pin to a logic low
+void go_0(int pin)
+{
+  pinMode(pin, OUTPUT);
+  digitalWrite(pin, LOW);
+}
+// Function to send the Touchpad a command
+void touchpad_write(char data)
+{
+  char i;
+  char parity = 1;
+ // put pins in output mode 
+  go_z(MDATA);
+  go_z(MCLK);
+  elapsedMillis watchdog; // set watchdog to zero
+  delayMicroseconds(300);
+  go_0(MCLK);
+  delayMicroseconds(300);
+  go_0(MDATA);
+  delayMicroseconds(10);
+  // start bit 
+  go_z(MCLK);
+  // wait for touchpad to take control of clock)
+  while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag
+      break;
+    }
+  }
+  // clock is low, and we are clear to send data 
+  for (i=0; i < 8; i++) {
+    if (data & 0x01) {
+      go_z(MDATA);
+    } 
+    else {
+      go_0(MDATA);
+    }
+    // wait for clock cycle 
+    while (digitalRead(MCLK) == LOW) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }      
+    while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+    parity = parity ^ (data & 0x01);
+    data = data >> 1;
+  }  
+  // parity 
+  if (parity) {
+    go_z(MDATA);
+  } 
+  else {
+    go_0(MDATA);
+  }
+ // wait for clock cycle
+  while (digitalRead(MCLK) == LOW) {
+  if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }  
+  while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }  
+  // stop bit 
+  go_z(MDATA);
+  delayMicroseconds(50);
+  while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  // wait for touchpad to switch modes 
+  while ((digitalRead(MCLK) == LOW) || (digitalRead(MDATA) == LOW)) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  // put a hold on the incoming data. 
+  go_0(MCLK);
+}
+
+//
+// Function to get a byte of data from the touchpad
+//
+char touchpad_read(void)
+{
+  char data = 0x00;
+  int i;
+  char bity = 0x01;
+  // start the clock 
+  elapsedMillis watchdog; // set watchdog to zero
+  go_z(MCLK);
+  go_z(MDATA);
+  delayMicroseconds(50);
+  while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  delayMicroseconds(5);  // wait for clock ring to settle 
+  while (digitalRead(MCLK) == LOW) {  // eat start bit 
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  for (i=0; i < 8; i++) {
+    while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+    if (digitalRead(MDATA) == HIGH) {
+      data = data | bity;
+    }
+    while (digitalRead(MCLK) == LOW) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+    bity = bity << 1;
+  }
+  // ignore parity bit  
+  while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  while (digitalRead(MCLK) == LOW) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  // eat stop bit 
+  while (digitalRead(MCLK) == HIGH) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  while (digitalRead(MCLK) == LOW) {
+    if (watchdog >= 200) { //check for infinite loop
+      touchpad_error = HIGH; // set error flag       
+      break;
+    }
+  }
+  // put a hold on the incoming data. 
+  go_0(MCLK);
+  return data;
+}
+
+void touchpad_init()
+{
+  touchpad_error = LOW; // start with no error
+  go_z(MCLK); // float the clock and data to touchpad
+  go_z(MDATA);
+  //  Sending reset to touchpad
+  touchpad_write(0xff);
+  touchpad_read();  // ack byte
+  //  Read ack byte
+  touchpad_read();  // blank 
+  touchpad_read();  // blank 
+  // Default resolution is 4 counts/mm which is too small
+  //  Sending resolution command
+  touchpad_write(0xe8);
+  touchpad_read();  // ack byte
+  touchpad_write(0x03); // value of 03 gives 8 counts/mm resolution
+  touchpad_read();  // ack byte
+  //  Sending remote mode code so the touchpad will send data only when polled
+  touchpad_write(0xf0);  // remote mode 
+  touchpad_read();  // Read ack byte 
+  delayMicroseconds(100);
+}
+// ************************************Begin Routine*********************************************************
+void setup()
+{
+  touchpad_init(); // reset touchpad, then set it's resolution and put it in remote mode 
+  if (touchpad_error) {
+    touchpad_init(); // try one more time to initialize the touchpad
+  }
+}
+
+// declare and initialize variables  
+  char mstat; // touchpad status reg = Y overflow, X overflow, Y sign bit, X sign bit, Always 1, Middle Btn, Right Btn, Left Btn
+  char mx; // touchpad x movement = 8 data bits. The sign bit is in the status register to 
+           // make a 9 bit 2's complement value. Left to right on the touchpad gives a positive value. 
+  char my; // touchpad y movement also 8 bits plus sign. Touchpad movement away from the user gives a positive value.
+  boolean over_flow; // set if x or y movement values are bad due to overflow
+  boolean left_button = 0; // on/off variable for left button = bit 0 of mstat
+  boolean right_button = 0; // on/off variable for right button = bit 1 of mstat
+  boolean old_left_button = 0; // on/off variable for left button status the previous polling cycle
+  boolean old_right_button = 0; // on/off variable for right button status the previous polling cycle
+  boolean button_change = 0; // Active high, shows when a touchpad left or right button has changed since last polling cycle
+  
+// ************************************Main Loop***************************************************************
+void loop() {
+// poll the touchpad for new movement data
+  over_flow = 0; // assume no overflow until status is received 
+  touchpad_error = LOW; // start with no error
+  touchpad_write(0xeb);  // request data
+  touchpad_read();      // ignore ack
+  mstat = touchpad_read(); // save into status variable
+  mx = touchpad_read(); // save into x variable
+  my = touchpad_read(); // save into y variable
+  if (((0x80 & mstat) == 0x80) || ((0x40 & mstat) == 0x40))  {   // x or y overflow bits set?
+    over_flow = 1; // set the overflow flag
+  }   
+// change the x data from 9 bit to 8 bit 2's complement
+  mx = mx >> 1; // convert to 7 bits of data by dividing by 2
+  mx = mx & 0x7f; // don't allow sign extension
+  if ((0x10 & mstat) == 0x10) {   // move the sign into 
+    mx = 0x80 | mx;              // the 8th bit position
+  } 
+// change the y data from 9 bit to 8 bit 2's complement and then take the 2's complement 
+// because y movement on ps/2 format is opposite of touchpad.move function
+  my = my >> 1; // convert to 7 bits of data by dividing by 2
+  my = my & 0x7f; // don't allow sign extension
+  if ((0x20 & mstat) == 0x20) {   // move the sign into 
+    my = 0x80 | my;              // the 8th bit position
+  } 
+  my = (~my + 0x01); // change the sign of y data by taking the 2's complement (invert and add 1)
+// zero out mx and my if over_flow or touchpad_error is set
+  if ((over_flow) || (touchpad_error)) { 
+    mx = 0x00;       // data is garbage so zero it out
+    my = 0x00;
+  } 
+// send the x and y data back via usb if either one is non-zero
+  if ((mx != 0x00) || (my != 0x00)) {
+    Mouse.move(mx,my);
+  }
+//
+// send the touchpad left and right button status over usb if no error
+  if (!touchpad_error) {
+    if ((0x01 & mstat) == 0x01) {   // if left button set 
+      left_button = 1;   
+    }
+    else {   // clear left button
+      left_button = 0;   
+    }
+    if ((0x02 & mstat) == 0x02) {   // if right button set 
+      right_button = 1;   
+    } 
+    else {   // clear right button
+      right_button = 0;  
+    }
+// Determine if the left or right touch pad buttons have changed since last polling cycle
+    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 button status
+    }
+    old_left_button = left_button; // remember new button status for next polling cycle
+    old_right_button = right_button;
+  }
+//
+// **************************************End of touchpad routine***********************************
+// 
+  delay(30);  // wait 30ms before repeating next polling cycle
+}