add pendulum example, fix missing MEL_API in serial port

examples/CMakeLists.txt

@@ -37,6 +37,7 @@ if(QUANSER)
     mel_example(haptic_paddle)
     mel_example(overview)
     mel_example(ati_sensor)
+    mel_example(pendulum)
 endif()
 
 if(NI_ARM)

examples/ex_pendulum.cpp

@@ -0,0 +1,95 @@
+// MIT License
+//
+// MEL - Mechatronics Engine & Library
+// Copyright (c) 2019 Mechatronics and Haptic Interfaces Lab - Rice University
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// Author(s): Evan Pezent (epezent@rice.edu)
+
+#include <MEL/Daq/Quanser/Q8Usb.hpp>
+#include <MEL/Mechatronics.hpp>
+#include <MEL/Communications.hpp>
+#include <MEL/Core.hpp>
+#include <MEL/Math.hpp>
+#include <MEL/Devices/Windows/Keyboard.hpp>
+
+using namespace mel;
+
+// create global stop variable CTRL-C handler function
+ctrl_bool stop(false);
+bool handler(CtrlEvent event) {
+    if (event == CtrlEvent::CtrlC)
+        stop = true;
+    return true;
+}
+
+int main() {
+    // register handler to gracefully exit program
+    register_ctrl_handler(handler);
+    // create Q8 USB DAQ
+    Q8Usb q8;
+    q8.open();
+    q8.enable();
+    // set encoder deg/count
+    q8.encoder[0].set_units_per_count(2 * PI / 500); 
+    q8.encoder[0].zero();
+    // melshare for external scoping
+    MelShare ms("pendulum");
+    // constants
+    const double sense_gain = 2.20; // A/V
+    const double commd_gain = 0.5;  // A/V
+    const double kp = 5.0;          // A/rad
+    const double kd = 0.5;          // A*s/rad
+    const double ref = PI;          // radians
+    // PD controlelr (I = 0)
+    PidController pd(kp, kd, 0);
+    // control loop timer
+    Timer timer(hertz(1000));
+    // start Q8 watchdog
+    q8.watchdog.start();
+    while (!stop) {
+        // get current time
+        Time t = timer.get_elapsed_time_actual();
+        // sync Q8 input with real world
+        q8.update_input();
+        // enable/disable pendulum
+        if (Keyboard::is_key_pressed(Key::Up))              // enable
+            q8.DO[0].set_value(High); 
+        else if (Keyboard::is_key_pressed(Key::Down))       // disable
+            q8.DO[0].set_value(Low);
+        // get current pendulum state
+        double pos = q8.encoder[0].get_position();          // rad
+        double vel = q8.encoder[0].get_velocity();          // rad/s
+        // wrap position to pi so controller behaves
+        pos = wrap_to_pi(pos);                              // rad
+        // measure actual current
+        double sense_volt = q8.AI[0].get_value();           // V
+        double sense_curr = sense_volt * sense_gain;        // A
+        // compute PD controller command
+        double commd_curr = pd.calculate(ref, pos, vel, t); // A
+        double commd_volt = commd_curr / commd_gain;        // V
+        // set command
+        q8.AO[0].set_value(commd_volt);
+        // write data to melshare for scoping
+        ms.write_data({ pos, vel, sense_curr, commd_curr });
+        // sync output w/ real world
+        q8.update_output();
+        // kick watchdog
+        q8.watchdog.kick();
+        // wait for next timestep
+        timer.wait();
+    }    
+    // shutdown Q8
+    q8.disable();
+    q8.close();  
+    return 0;
+}

include/MEL/Communications/SerialPort.hpp

@@ -23,7 +23,7 @@
 namespace mel {
 
 /// Interface to RS-232 Serial Port
-class SerialPort : NonCopyable {
+class MEL_API SerialPort : NonCopyable {
 public:
 
     /// Constructor

include/MEL/Mechatronics.hpp

@@ -24,6 +24,7 @@
 #include <MEL/Mechatronics/Limiter.hpp>
 #include <MEL/Mechatronics/Motor.hpp>
 #include <MEL/Mechatronics/PdController.hpp>
+#include <MEL/Mechatronics/PidController.hpp>
 #include <MEL/Mechatronics/PositionSensor.hpp>
 #include <MEL/Mechatronics/Robot.hpp>
 #include <MEL/Mechatronics/VelocitySensor.hpp>