Garbage returning from GPS EM406-A (Arduino UNO) - SOLVED

Using Arduino Networking, Protocols, and Devices
6

Thanks for all that replied.

Well, I tried to solve the issue by software with no success. The code below is a stripped down
version of code posted elsewhere as an example on how to get data from the EM406-A. I´ve
changed it to read all data in a buffer first, to avoid timing issues, and changed the logic of
detecting IDLE and START bits. Got no valid data for all combinations.

#define bit4800Delay 188
#define halfBit4800Delay 94

byte rx = 7;

// Control logic for IDLE, START BIT, etc.
byte IDLE;
byte START;

// EM406 serial content is stored here
#define MAX_SIZE 1100
byte output[ MAX_SIZE ];

void setup() {
  pinMode( rx, INPUT );
  Serial.begin( 9600 );
  // Init buffer with all 1s
  for( int i = 0; i < MAX_SIZE; i++ ) {
    output[i] = 255;
  }
}

char SWread() {
  byte val = 0;
  while (digitalRead(rx) == IDLE );
  //wait for start bit
  if( digitalRead(rx) == START ) {
    delayMicroseconds( halfBit4800Delay );
    for (int offset = 0; offset < 8; offset++) {
	delayMicroseconds( bit4800Delay );
	val |= digitalRead( rx ) << offset;
    }
    //wait for stop bit + extra
    delayMicroseconds(bit4800Delay);
    delayMicroseconds(bit4800Delay);
    return val;
  } else {
    return 'A';
  }
}

void loop()
{
  // Inverted logic for IDLE and START bits. Tried
  // also with IDLE=HIGH and START=LOW
  IDLE = LOW;
  START = HIGH;
  for( int i = 0; i < MAX_SIZE; i++ ) {
    output[i] = SWread();    
  }
  Serial.println( "Direct" );
  for( int i = 0; i < MAX_SIZE; i++ ) {
    Serial.print( output[i], BYTE );
  }
  Serial.println( "Inverse" );
  for( int i = 0; i < MAX_SIZE; i++ ) {
    byte inv = ~output[i];
    Serial.print( inv, BYTE );
  }
  while( 1 ) {
  }
}

With or without the inversion guess the way to go is first convert the signal levels to
0~5V just to be sure.

In the meantime it would be great to have any report on the use of this module
with the Uno.