Turning LED on and off with C++ (using CPPWindows)

Projects Interfacing w/ Software on the Computer
1

So, since I normally despise interpreted languages (Python being the sole exception so far), I've been trying to get an LED to blink on my Uno with C++ and a winform. With very similar code and the same circuit using Processing I was able to turn the LED on and off with two buttons from my computer, but am having no luck with C++.

I compiled CPPWindows to a static library and it works fine on its own; my program is the problem. I made a simple winform with two buttons, one to turn the LED on and the other off, but it does not function as intended. When I click either button, the RX light on the Uno lights up, so I know it's receiving data, but apparently not the right data. Here's what I have so far:

#include <Arduino\SerialClass.h>
#include "Send.h"
#include "led.h"

namespace ledtest {
	Serial* SP = new Serial("COM3");

	[STAThread]
	void main(array<String^>^ args) {

		Application::EnableVisualStyles();
		Application::SetCompatibleTextRenderingDefault(false);

		ledtest::led form;
		Application::Run(%form);
	}

	void sendState(int state) {
		if (state == 1)
			SP->WriteData("1", 1);
		if (state == 0)
			SP->WriteData("0", 1);
	}	
        
        void readState() {
		char* iState;

		while (SP->IsConnected()) {
			SP->ReadData(iState, 255);
			printf(iState);
		}
	}

The button click events are as follows:

	private: System::Void btnHigh_Click(System::Object^  sender, System::EventArgs^  e) {
				 ledtest::sendState(1);
			 }
	private: System::Void btnLow_Click(System::Object^  sender, System::EventArgs^  e) {
				 ledtest::sendState(0);
			 }

My Arduino sketch:

int led = 12;
char* state;

// the setup routine runs once when you press reset:
void setup() {
  Serial.begin(9600);
  pinMode(led, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  if (Serial.available()) {
    Serial.readBytes(state, 1);
    
    if (state == "1")
      digitalWrite(led, HIGH);
    if (state == "0")
      digitalWrite(led, LOW);
    else {
      Serial.println(state);
    }
  }
}

CPPWindows' WriteData function requires char*, so that's why I am sending "1" instead of just a 1. In the sketch I read one byte (the character "1"), and then set the pin as high or low depending on the variable "state".

However, the data sent from the C++ program is apparently not sent correctly (or I am sending it incorrecty) and the LED never turns on. Also, the C++ program never prints what the actual variable is. Even if the variable from the Uno can't be read it should at least return a "-1", but it returns nothing.

I'm all out of ideas on what to do, so any help would be appreciated. Thanks!

2

'm all out of ideas on what to do

Ditch the convoluted Microslop abomination of C++, and use C# instead. Much easier to design forms, program callbacks, etc. AND support for the serial port is built in. Read and write like a file.

3

You insult Microsoft's C++, but you like C#, which they had much more to do with than C++? :stuck_out_tongue:

I guess I could use C#. I've used it in the past, but prefer sticking with C/C++ since it's much more easily cross-compiled. No need to worry about Mono.

And I realize this program is completely Windows dependent, but the more C++ experience I can get, the better.

So I can switch to C#, but if anyone could help me with this I'd much prefer that.

4

You insult Microsoft's C++, but you like C#, which they had much more to do with than C++?

Yes. What the hell is this?

	private: System::Void btnHigh_Click(System::Object^  sender, System::EventArgs^  e) {

An Object^ is not standard C++.

    Serial.readBytes(state, 1);

It hardly makes sense to use a function that can read multiple bytes to read one. Use read(), instead.

char* state;

state is a pointer. It doesn't point to anything. You can't pass a NULL pointer to readBytes() and expect it to write the data somewhere usable.

5

read() requires an int, and since WriteData() requires a char*, I don't know if that would work well.

Yeah, that's my bad. I haven't done any programming in about 3 months, and even then most of what I did was x86 assembly, so I've forgotten a lot of C++. I actually much prefer assembly over any other language; even though it's anything but terse, everything is explicit. I always have trouble understanding implicit, complex, convoluted things. But even then I was still an amateur programmer.

With MASM at least, once can initialize a variable of indeterminate size (in the .data? section, and the program can do with it as it pleases, so I guess I figured I could do the same here. :stuck_out_tongue:

Would char* state = new char[#] be correct? Or how would you recommend I send the data from my computer to the Arduino?

6

read() requires an int, and since WriteData() requires a char*, I don't know if that would work well.

read() doesn't require anything. It returns an int. The only reason it returns an int, instead of a char or byte, is to allow the function to return an error if there is nothing to read. You can cast the return to a char, implicitly or explicitly.

You can use readBytes() but not with a NULL pointer. You must make the pointer point somewhere first. The simplest method is to not use a pointer at all. Use an array, instead.

char state[2];

Serial.readBytes(state, 1);
if(state[0] == '1')
   // do the one thing
else if state[0] == '0')
   // do the zero thing
7

Well, I changed the sketch to what you provided, and it works. Thank you kindly.

However, I still can't get the ReadData() to work. Here's what I changed my program to:

	void readState() {
		char iState[2];

		while (SP->IsConnected()) {
			SP->ReadData(iState, 1);
			printf("%s", iState[0]);
		}
	}

And the sketch:

    if (state[0] == '1') {
      digitalWrite(led, HIGH);
      Serial.println(state[0]);
    }
    if (state[0] == '0') {
      digitalWrite(led, LOW);
      Serial.println(state[0]);
    }

The LED turns on and off as expected, but I still get no console output on my C++ program. Do you see anything glaringly obvious?

8

Serial.println(state[ 0 ]) sends three characters. You are attempting to read only one of them. That's not a good match.

What is supposed to trigger a call to readState()? Add a printf() to just print a message like "Hey, I got called!". Does that get printed?

9

Shit, you're right. That's what I get for staying up so long.

So after declaring the function and calling it from main, it still doesn't work. It only does when I close the winform, then the console works. Probably because both appear only because I have the subsystem unset. I'll find a different way to show the text in the program. If only I could figure out how to set the text of a textbox from the main source file...