Arduino output pin outputs random activity - c

Question

I am working on an Arduino project controlling a DIY RC truck that reads the output pins of an RC reciever and is supposed to PWMs a couple of pins accordingly. The pins are hooked onto a motor controller that takes PWM.
That is where the problem comes in. My reverse is working perfectly, but on the pin that does forward, I only get random activity. I'm using the Arduino Mega 2560.
Here is the code. The problem has been posted below it:
#include <Servo.h>
//Create variables for three channels
int RXCH[3];
volatile int RXSG[3];
int RXOK[3];
int PWMSG[3];
byte vooruit;
byte achteruit;
Servo stuur;
int mv = 13;
int ma = 10;
void setup() {
Serial.begin(115200);
stuur.attach(8);
//Assign PPM input pins. The receiver output pins are conected as below to non-PWM Digital connectors:
RXCH[0] = 6; //Throttle
RXCH[1] = 7; //Steering
//RXCH[2] = 5; //Nothing yet
//RXCH[3] = 2; //Nothing yet
//RXCH[4] = 7; //Nothing yet
//RXCH[5] = 8; //Nothing yet
for (int i = 0; i < 3; i++){
pinMode(RXCH[i], INPUT);
}
//TCCR1B = TCCR1B & 0b11111000 | 0x01;
//TCCR2B = TCCR2B & 0b11111000 | 0x01;
}
void loop() {
// Read RX values
for (int i = 0; i < 3; i++){ //For each of the 6 channels:
RXSG[i] = pulseIn(RXCH[i], HIGH, 20000); //Read the receiver signal
if (RXSG[i] == 0) { //Error catching
RXSG[i] = RXOK[i];
} else {
RXOK[i] = RXSG[i];
}
//Substitute the high values to a value between -255 and 255
PWMSG[0] = map(RXSG[0], 1000, 2000, -255, 255);
//Servo values, calibrated according to my steering servo.
PWMSG[1] = map(RXSG[1], 1000, 2000, 24, 169);
//Make sure that the value stays within the desired boundaries.
constrain (PWMSG[i], -255, 255);
//For debugginf purposes
Serial.print(" || Ch: ");
Serial.print(i);
Serial.print(" / PWMSG: ");
Serial.print(PWMSG[i]);
}
delay (5);
// Car goes forwards
if (PWMSG[0] > 40)
{
MV();
}
// Car goes backwards
if (PWMSG[0] < -40)
{
MA();
}
// Car stops
else
{
stopmotor();
}
stuur.write(PWMSG[1]);
Serial.println();
}
void MV()
{
vooruit = PWMSG[0];
analogWrite (mv, vooruit);
digitalWrite (ma, LOW);
Serial.print(" vooruit: ");
Serial.print(vooruit);
}
void MA()
{
achteruit = abs(PWMSG[0]);
analogWrite (ma, achteruit);
digitalWrite (mv, LOW);
Serial.print(" achteruit: ");
Serial.print(achteruit);
}
void stopmotor()
{
digitalWrite (ma, LOW);
digitalWrite (mv, LOW);
}
I don't really know if the code is considered pretty, or if I made some basic mistakes for that matter.
This is one of my first projects that I tried to do the right way, making comments and such, all well commented criticism is welcome.
What the code is supposed to do:
Move the stick on the transmitter forwards, the car goes forwards, and speed should be according to position of the stick.
Move the stick on the transmitter backwards, the car goes backwards, and speed should be according to position of the stick.
Move stick on the transmitter left or right, the servo in the car should react according to the value the Arduino calculated. You might wonder why I don't place the servo directly on the transmitter. Well, that's because I have many more future things in mind with this project, and now I can calibrate it way easier.
Problem:
When I move the stick on the transmitter forwards, and the Serial monitor is open, I get the right values on the Serial monitor, but the LED present on pin 13 just randomly blinks, very dim I must say.
I already tried to replace things like byte with int, but it had no effect. The rest of the code works fine.
Using some new code, I get a Serial response from every "stage", except the final stages that controls the pins.
#include <Servo.h>
//Create variables for channels
Servo wheel;
int MFORWARD_PIN = 13;
#define MBACKWARD_PIN 10
#define WHEEL_PIN 8
#define THROTTLE_PIN 6
#define STEERING_PIN 7
void setup() {
Serial.begin(115200);
wheel.attach(WHEEL_PIN);
pinMode(THROTTLE_PIN, INPUT);
pinMode(STEERING_PIN, INPUT);
pinMode(MFORWARD_PIN, OUTPUT);
pinMode(MBACKWARD_PIN, OUTPUT);
//TCCR1B = TCCR1B & 0b11111000 | 0x01;
//TCCR2B = TCCR2B & 0b11111000 | 0x01;
}
void loop() {
int throttle = read_throttle();
int steering = read_steering();
delay (5);
throttle_handle(throttle);
steering_handle(steering);
}
// Read RX values
int read_throttle(){
int throttle = pulseIn(THROTTLE_PIN, HIGH, 20000);
throttle = map(throttle, 1000, 2000, -255, 255); //Substitute the high values to a value between -255 and 255.
constrain (throttle, -255, 255); //Make sure that the value stays within the desired boundaries.
//Serial.println(throttle);
}
int read_steering() {
int steering = pulseIn(STEERING_PIN, HIGH, 20000);
steering = map(steering, 1000, 2000, 24, 169); //Servo values, calibrated according to my steering servo.
constrain (steering, 24, 169); //Make sure that the value stays within the disired boundaries.
//Serial.println("steering");
}
void move_forward(int val) {
analogWrite (MFORWARD_PIN, val);
digitalWrite (MBACKWARD_PIN, LOW);
Serial.print(" vooruit: ");
Serial.print(val);
}
void move_backward(int val)
{
val = abs(val);
analogWrite (MBACKWARD_PIN, val);
digitalWrite (MFORWARD_PIN, LOW);
Serial.print(" achteruit: ");
Serial.print(val);
}
void move_stop()
{
digitalWrite (MFORWARD_PIN, LOW);
digitalWrite (MBACKWARD_PIN, LOW);
}
void throttle_handle(int throttle) {
//Serial.print("throttle");
if (throttle > 40) {
move_forward(throttle);
}
if (throttle < -40) {
move_backward(throttle);
}
else {
move_stop();
}
}
void steering_handle(int steering) {
wheel.write(steering);
// Serial.println("steering:");
// Serial.print(steering);
}

Answer 1

Unused index:
Everywhere you loop over three values, whereas you only use two items in the array. So you'd better change all your sizes to 2 instead of 3, or you can define a NB_INPUT constant at the top of your source code, that you can change easily for more flexibility:
#define NB_INPUT 2
...
for (int i = 0; i<NB_INPUT; ++i) {
...
RXOK in setup():
your comment about arrays is justified, the first bug I can see in your code is that you read from the RXOK array, whereas you did not put any values in it. If you're sure that RXSG gets only zeroes from pulseIn() on the first pass of the Read RX values loop it can be ok, but I doubt it is. e.g.:
for (int i=0; i<3; ++i)
RXOK[i] = 0;
So you should put values in RXOK values in setup().
constant indexes in a for loop:
Then you map() the values from 1000->2000 to -255->255 for RXSG[0] and RXSG[1] inside the for loop, which will be done for the three iterations. I'm not sure what you want there, but if you want to do it for constant indexes, you'd better do it outside of the loop. But as you're checking a constraint on the -255->255 domain for each value of the iteration loop, I think you may want to do it on relative values:
PWMSG[i] = map(RXSG[i], 1000, 2000, -255, 255);
but it seems the domain is dependent on the index, so you may want to make a couple of defines at the top of your source code:
#define THROTTLE_IDX 0
#define STEERING_IDX 1
and put your map() in a if statement:
if (i == THROTTLE_IDX)
PWMSG[i] = map(RXSG[i], 1000, 2000, -255, 255);
elif (i == STEERING_IDX)
PWMSG[i] = map(RXSG[i], 1000, 2000, 24, 169);
# add a else statement if you need to do a map for the other values of the array
constrain(PWMSG[i], -255, 255)
general algorithm
I'm not sure you really need an array for your use case. You'd better keep a few variables around and have a better use of functions for your code to be readable and less bugprone:
#define THROTTLE_PIN 6
#define STEERING_PIN 7
#define WHEEL_PIN 8
#define MFORWARD_PIN 13
#define MBACKWARD_PIN 10
Servo wheel;
// sets up the arduino
void setup() {
Serial.begin(115200);
wheel.attach(WHEEL_PIN);
pinMode(THROTTLE_PIN, INPUT);
pinMode(STEERING_PIN, INPUT);
}
// input data handling
int read_throttle() {
int throttle = pulseIn(THROTTLE_PIN, HIGH, 20000);
return map(throttle, 1000, 2000, -255, 255);
}
int read_steering() {
int steering = pulseIn(STEERING_PIN, HIGH, 20000);
return map(throttle, 1000, 2000, 24, 169);
}
// output actions handling
void move_forward(int val) {
analogWrite(MFORWARD_PIN, val);
digitalWrite(MBACKWARD_PIN, LOW);
// Serial.print...
}
void move_backward(int val) {
analogWrite(MFORWARD_PIN, val);
digitalWrite(MBACKWARD_PIN, LOW);
// Serial.print...
}
void stop_motor() {
digitalWrite(MFORWARD_PIN, LOW);
digitalWrite(MBACKWARD_PIN, LOW);
}
void handle_throttle(int throttle) {
if (throttle > 40)
move_forward(throttle);
elif (throttle < -40)
move_backward(throttle);
else
stop_motor();
}
// general algorithm
void loop() {
int throttle = read_throttle();
delay(5);
handle_throttle(throttle);
}
There are more code duplication, but sometimes it is better to duplicate code than to make a code almost unreadable, and hard to debug while not offering any kind of flexibility/modularity. And here are a few other things I found in your code that should be corrected:
Naming convention: try to use good names for your functions (two letters variables, or dutch variables are not a good idea, I'm not english native and I always avoid to use my own language based names in code even for code I don't share, you never know who will read your code in 2 days, 2 months, or 2 years).
globals: Try to avoid using global variables as much as possible. Declare only constant in the global scope : const int foo = 1; or preprocessor defines #define foo 1, so that you do not spend too much of the little RAM space you have on your arduino. The only exception to that rule, which is very specific to arduino development, are objects (like Servo in your code) that you need to declare globally so you can set them up in the setup() function, and use them in the loop() function.
If I extrapolate on what you've written, you may want to add a handle_steering() function such as:
void handle_steering(int steering) {
if (steering > NN)
turn_left(steering);
elif (steering < NN)
turn_right(steering);
else
keep_straight();
}
and change the loop() to :
void loop() {
int throttle = read_throttle();
int steering = read_steering();
delay(5);
handle_throttle(throttle);
handle_steering(steering);
}
To make it a more general case of handling dynamically and flexibly a number of features, you could keep a few arrays:
PIN[]: containing the pins,
DOM_MIN[]: containing the minimum of the features' domain (for the map),
DOM_MAX[]: containing the maximum of the features' domain (for the map),
BOUND_MIN[]: containing the minimum boundaries (for the handle_steering condition),
BOUND_MAX[]: containing the maximum boundaries (for the handle_steering condition),
ACTION[]: containing the pointers to functions.
and then your algorithm would look like:
int read_input(int i) {
int value = pulseIn(PIN[i], HIGH, 20000);
return map(value, 1000, 2000, DOM_MIN[i], DOM_MAX[i]);
}
int handle_action(int i, int value) {
if (value > BOUND_MIN[i])
*(ACTION[i])(value);
elif (value < BOUND_MAX[i])
*(ACTION[i])(value);
else
*(ACTION[i])(-1);
}
void loop() {
for (int i=0; i<NB_INPUTS; ++i) {
int value = read_input(i);
delay(5);
handle_action(i, value);
}
}
but as you're still not comfortable with arrays (and I assume pointers as well), I would not recommend going further that way for the time being. First do it simple and make it work and then you could try to factorize it following the idea I'm exposing here. But you're making a software that is embedded, where the RAM is rare and the processing power is low, while your code space is cheap. So it's one of the few occasions where you'd better want to make a more redundant code that will stay in program space, whereas you want to manipulate as little symbols in the RAM. That's why I'm not showing you how the arrays are being declared/defined, and how to handle function pointers, because I don't think that solution (where you were heading) is the right way to do what you want.
Always remember, simpler is better!
HTH