RPi to Arduino thru rs485 not receiving all characters

Question

I have this USB to RS485 Converter plugged on the RPi and have this TTL to RS485 connected to the Arduino Nano. I am using 9600 baud rate. I need to send max 16 characters in each direction but when I try sending, on the receiving end I receive only the first 11 characters... If I connect the Arduino Nano using usb cable to the RPi the communication is going perfectly...

This is the Arduino code:

int rs485CtrlPin = 6;

void setup() {
  pinMode(rs485CtrlPin, OUTPUT);
  Serial.begin(9600);
  while (!Serial);
}

void loop() {
  digitalWrite(rs485CtrlPin, HIGH);   
  Serial.println("cmd1,12345678901");
  delay(10);
  digitalWrite(rs485CtrlPin, LOW);    
  delay(5000);
}

This is the Python code:

import serial
import time
import datetime

ts = time.time()
st = datetime.datetime.fromtimestamp(ts).strftime('%Y-%m-%d %H:%M:%S')
print st + ": Session started!"
ser = serial.Serial('/dev/ttyUSB0', 9600, timeout=0)
while True:
    try:
        if(not(ser.isOpen())):
            ser.open()
        cmd = ser.readline()
        ts = time.time()
        st = datetime.datetime.fromtimestamp(ts).strftime('%Y-%m-%d %H:%M:%S')
        print st + ": " + cmd
    except Exception as ex:
        error = "Exception is: " + ex.__str__()
        if(not(ser == None)):
            ser.close()
            ser = None
            ts = time.time()
            st = datetime.datetime.fromtimestamp(ts).strftime('%Y-%m-%d %H:%M:%S')
            print st + ": " + error

So instead receiving "cmd1,12345678901" I get "cmd1,123456".

Have in mind that even if I connect the Arduino Nano on my PC using the same RS485 converters and use the Serial Monitor of the Arduino IDE I get the same result... If I set the baud rate to 115200 I receive 2 more characters "cmd1,12345678" but since I will use the RS485 for more than 50m distance I might need to use max 9600 baud rate...

Uncontrolled Crowd Uncontrolled Crowd · Accepted Answer · 2018-05-11T13:37:40

Thanks to the user Riva from the Arduino forum I found how stupid I am... In the Arduino code I added 10ms delay between sending data and turning off the transmit pin for the RS485, with 9600 baud rate (1200 bytes per second) you can only send 12 bytes. To use the full 1200 bytes data transfer you need to add delay of 1 second (which is obvious when you think about it and I didnt it seems)...

The full topic on the Arduino forum can be found here.

RPi to Arduino thru rs485 not receiving all characters

1 Answers