Weird behavior with SoftwareSerial and pin choices

I am creating a heads-up display that displays the arguments being passed to a motor controller (e.g. speed as a 0-127 value) and a bearing (N/S/E/W). For the moment, the bearing is hardcoded, but that should change once I actually get my compass chip.

If I include a SoftwareSerial connection but don’t actually send any commands to the motor controller, the overlay works perfectly.

If I send commands to the motor controller via the softwareserial connection, the video goes wonky.

Here’s the weirdest part: the overlay changes depending on which TX/RX pins I use for the motor controller. Pins 2/3 get me very faint overlay that rolls. Pins 4/5 and 12/13 get me video that’s readable, but glitches to the lower right every few seconds.

Any advice would be helpful.

#include <TVout.h>
#include <fontALL.h>
#define TXPIN 12
#define RXPIN 13
#include "SoftwareSerial.h"
// Create an instance of the software serial
// communication object. This represents the
// interface with the TReX Jr device
SoftwareSerial pololu(RXPIN, TXPIN);

#define W 136
#define H 96

TVout tv;

char s[17];
char h[1];
void setup()  {
  tv.begin(NTSC, W, H);
  initOverlay();
  tv.select_font(font6x8);
  tv.fill(0);
  pinMode(RXPIN, INPUT);
  pinMode(TXPIN, OUTPUT);

  // Begin communicating with the pololu interface
  pololu.begin(19200);
  delay(5);
}

// Initialize ATMega registers for video overlay capability.
// Must be called after tv.begin().
void initOverlay() {
  TCCR1A = 0;
  // Enable timer1.  ICES0 is set to 0 for falling edge detection on input capture pin.
  TCCR1B = _BV(CS10);

  // Enable input capture interrupt
  TIMSK1 |= _BV(ICIE1);

  // Enable external interrupt INT0 on pin 2 with falling edge.
  EIMSK = _BV(INT0);
  EICRA = _BV(ISC01);
}

// Required to reset the scan line when the vertical sync occurs
ISR(INT0_vect) {
  display.scanLine = 0;
}

void loop() {

int i = 0;
  sprintf(s, "The speed is:%u", i);
  tv.print(0, 0, s);
  sprintf(h,"Heading:%c",'N');
  tv.print(0,85,h);
  SetSpeed(1,true,i);
 
}
void SetSpeed(int MotorIndex, boolean Forward, int Speed)
{
  // Validate motor index
  if(MotorIndex < 0 || MotorIndex > 2)
    return;

  // Validate speed
  if(Speed < 0)
    Speed = 0;
  else if(Speed > 127)
    Speed = 127;

  // Send the "set" command based on the motor
  // Note that we do not accelerate to the
  // speed, we just instantly set it
  unsigned char SendByte = 0;
  if(MotorIndex == 0)
    SendByte = 0xC2;
  else if(MotorIndex == 1)
    SendByte = 0xCA;
  else if(MotorIndex == 2)
    SendByte = 0xF0;

  // If we go backwards, the commands are the same
  // but minus one
  if(!Forward)
    SendByte--;

  // Send the set speed command byte
  pololu.write(SendByte);
  pololu.write(SendByte);
  

  // Send the speed data byte
  pololu.write(Speed);
}

• This topic was modified 5 years, 2 months ago by Perry.