Help with serial read

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi, i want to use arduino for reading power value from the ttl port of a power meter that i've purchased, i'm using this code:

#include <NewSoftSerial.h>

NewSoftSerial dev(2,3);

void setup(){
  dev.begin(115200);
  Serial.begin(115200);
}

void loop(){
  send: 
  dev.print('A'); //this is the power request
  delay(1000);
  while(dev.available()<5){
    goto send;
  }
  int readed=0;
  for(int i=0; i<4; i++){
    readed = readed|(dev.read()<<(8*i));
  }
  dev.read();
  Serial.println(readed, BIN);
  delay(1000);
}

the problem is that i recive wrong values like those:

11111111111111111000000011000011
11111111111111111000000011000010
11111111111111111000000010110111
11111111111111111000000011000001

what i can do??
where is the problem?
thanx.

2

the problem is that i recive wrong values

What values were you expecting?
What are the specs for this meter?

Rob

3

You are using a horrible goto loop to send 'A' over and over until you get 5 bytes to read. Then, you read and save 4 of them, and then throw the 5th one away. Why?

How do you know you are getting wrong values. Does the fact that you don't get the number you expect have anything to do with the fact that you are trying to store 32 bytes in a 16 byte integer?

4

I've to recive 4 byte rappresenting the power value from the less significative, then i recive another byte wich is the checksum.
i use this goto loop to ensure that the power meter has recived the call, with a single request sometimes it don't respond

5

the meter comunicate via TTL with a baud rate of 115200.
I expected to recive a number like
00000000 00000000 00000000 10101110

6

After your :-
Serial.println(readed, BIN);
put a :-
Serial.println(" ");
to separate your bytes.
However it does look like your number is upside down (0 -> 1 and 1 -> 0), can you check the TTL levels from your meter and see which way up they are supposed to be.

7

You still can't stuff 32 bits in a 16 bit variable. This MUST be the first problem you resolve.

8

That 'while...goto'.
It has to go.
It's just....wrong :-?

9

Removal of the goto by returning from loop() (just one of the possible ways)

void loop(){
  ...
  if (dev.available() < 5) return;
  ...  
}
10

Try reading things ONLY if you have enough data in the buffer.

void loop(){
  dev.print('A'); //this is the power request
  delay(1000);
  if(dev.available()>=5){
  int readed=0;
  for(int i=0; i<4; i++){
    Serial.print(dev.read(), BIN); 
   Serial.print(" ");
  }
  Serial.println(" ");
  delay(1000);
 }
}
11

ok i've deleted the goto loop and created a more readable code

void loop(){
  dev.print('A');
  delay(1000);
  word readed=0;
  if(dev.available()>=5){
    for(int i=0; i<4; i++){
      readed = readed|(dev.read()<<(8*i));
    }
    dev.read();
    Serial.println(readed, BIN);
    Serial.println(readed);
    delay(1000);
  }
}

but the problem is that i get uncorrect values like those:

1000000010111001
32953
1000000010111001
32953
1100000010111001
49337

when the real power is about 100W

12

is possible that the "newsoftwareserial" library has problem on the read function?

13

How many times do you want telling:-
for(int i=0; i<4; i++){
readed = readed|(dev.read()<<(8*i));
}

YOU CAN"T DO THAT!!! there are only 2 (TWO) bytes in an int.

14

@rferrazz
Start with unsigned long readed = 0; instead of int
read:
http://arduino.cc/en/Reference/Int
http://arduino.cc/en/Reference/UnsignedLong

15

is this ok?

void loop(){
  dev.print('A');
  delay(1000);
  unsigned long readed=0;
  if(dev.available()>=5){
    for(int i=0; i<4; i++){
      readed = readed|(dev.read()<<(8*i));
    }
    Serial.print("Checsum= ");
    Serial.println(dev.read());
    Serial.println(readed, BIN);
    Serial.println(readed);
    delay(1000);
  }
}

but the problem persist:

Checsum= 191
11111111111111111000000010111111
4294934719
Checsum= 191
11111111111111111000000010111111
4294934719
Checsum= 191
11111111111111111000000010111111
4294934719
16

The NewSoftSerial constructor has an optional 3rd argument, to invert the data coming in. Perhaps you need to find out what value to use, and use it.

      readed = readed|(dev.read()<<(8*i));

Why are you using |? After zeroing out the variable, you want to add the shifted value, don't you?

17

i'm using | because i've to add every time the morst significant byte, maintaining the bytes previously written

Like:
read: 01001111
readed=00000000 00000000 00000000 01001111

read:00000010
readed=00000000 00000000 00000010 01001111

... four times

18

the ttl port of a power meter that i've purchased,

Do you have a datasheet / type info of the powermeter to better understand what you are communicating with.

19

Each byte you read in is being shifted 0, 8, 16, or 24 bits before being OR'd with the other values. Since you initially set the value to 0, all 32 bits are 0. Shifting the byte to be incorporated means that it will only affect 8 bits if you ADD it.