Adding prints appears to change reads

Using Arduino Programming Questions
1

I have the following sketch:

#include <SoftwareSerial.h>
SoftwareSerial ser(3,8);
void setup() {
Serial.begin(9600);
ser.begin(9600);
}
void loop() {
static int i = 0;
while (ser.available()) {
char ch = ser.read();
Serial.print(ch);
ser.print(ch);
}
}

If I comment out the "ser.print(ch);" line, all works as I would expect, and the incoming serial data from my sensor is printed correctly to the Serial Monitor.

If I uncomment that line, the data that's written to the Serial Monitor becomes gibberish.

I can't think of any other changes. It replicates each time I do it:

  1. Comment out the line --> good data
  2. Uncomment the line --> bad data

I'm new to Arduino, so maybe I'm missing something basic, but that seems like a highly odd side effect. Why would that line alter what happens above it?

Thanks!

2

What sensor? How is all this wired up?

3

As I recall, doing writes (prints) with software serial turns interrupts off. With interrupts off, incoming data might be missed. Why are you sending data back to the sensor?

4

Or more specifically, What does the sensor do when you return it's output data as input data? confirm it?

Bob

5

OK, so that makes sense.

It's actually 2 sensors, one is a GPS (input) and one is a Bluetooth (output).

When I tried using 2 different SoftwareSerial objects, nothing worked at all.

I think I have an idea for how to get it to work.

Thanks for the answers/thoughts! I think they're really going to help!

6

I think I have an idea for how to get it to work.

Unless it involves different hardware, with multiple hardware serial ports, it won't work.