How can I send ASCII codes from raspberry Pi 3 to a serial device (printer, motor controller etc.) by using RS232 (9 pin-COM Port)?

Question

I want to learn how to send ASCII code from Raspberry Pi 3 to a serial device. Communication protocol of Serial device via RS232 (TX, RX pins). I was trying to connect from kermit as follows but I failed;

set line /dev/ttyS0
set carrier-watch off
set speed 9600
set flow none
set parity none set stop-bits 1
connect
The circuit with RS232-TTL Converter

The circuit with USB-TTL Profilic converter

Answer 1

I think this is possible with a Max232 chip or you can use a USB to Serial adapter.

http://elinux.org/RPi_VerifiedPeripherals#USB_UART_and_USB_to_Serial_.28RS-232.29_adapters

A USB to Serial (RS-232) adapter is used the other way around, ie. the USB end connects to the Raspberry Pi and the RS-232 end (DSUB-9 or DSUB-25 pin) to the other device which may be another computer, (old) modem or printer, or some electronic test equipment.

Answer 2

Finally I solved the problem by installing gtkterm on Raspberry Pi. After installing gtkterm I can send ASCII codes to the serial device (motor controller) and rotate the servo motor :)

Now all I need to write a Python program to control the motor. Can anybody help me about how I can write codes of gtkterm on Python?

Answer 3

Here is the Python code to control motor by using RPi3 and Copley motor driver. After installing gtkterm on Raspberry Pi 3 this code runs on Python 3 and the motor rotates 100000 counts incrementally for each running.

#This program is written by Mustafa Güler who is Electrical and Electronics Engineer
#at Teknolus Enerji located in METU Technopolis MET Campus.
#The main goal of this program is to make communication between RPi 3 Model B and
#Copley Motor Driver via serial communication protocol


import serial
import time

#Defining the port parameters
port = serial.Serial("/dev/ttyUSB0", baudrate=9600, timeout=3.0)

#Defining the Copley parameters

#Variables____________________bytearrays____________________________________________Copley Parameters
get_actual_motor_position   = [103, 32, 114, 48, 120, 51, 50, 13]                   # g r0x32
absolute_move               = [115, 32, 114, 48, 120, 99, 56, 32, 49, 13]           # s r0xc8 1
set_position                = [115,32,114,48,120,99,97,32,49,48,48,48,48,48,13]     # s r0xca [desired position; i.e. 100000]
abort_move                  = [116, 32, 48, 13]                                     # t 0
initiate_move               = [116, 32, 49, 13]                                     # t 1
initiate_homing             = [116, 32, 50, 13]                                     # t 2
amplifier_reset             = [114, 13]                                             # r
disable_amplifier           = [115, 32, 114, 48, 120, 50, 52, 32, 48, 13]           # s r0x24 0
get_bus_voltage             = [103, 32, 114, 48, 120, 49, 101, 13]                  # g r0x1e
get_amplifier_temperature   = [103, 32, 114, 48, 120, 50, 48, 13]                   # g r0x20
get_serial_baud_rate        = [103, 32, 114, 48, 120, 57, 48, 13]                   # g r0x90
set_function_gen_to_sine    = [115, 32, 114, 48, 120, 57, 56, 32, 50, 13]           # s r0x98 2
set_freq_for_function_gen_Hz= [115, 32, 114, 48, 120, 57, 57, 32, 49, 13]           # s r0x99 1
set_current_amplitude       = [115, 32, 114, 48, 120, 57, 97, 32, 49, 48, 48, 13]   # s r0x9a [current value; 100 for x0.01A]

while True:
    #Read the port information
    read_port = port.readline()

    #"s r0xca 100000" set position
    port.write(bytearray(set_position))
    print('set_position>>>', read_port)
    time.sleep(1)

    #"t 1" initiate move
    port.write(bytearray(initiate_move))
    time.sleep(2)
    print('initiate move>>>', read_port)

    #"g r0x32" get actual motor position
    port.write(bytearray(get_actual_motor_position))

    print('actual motor position>>', read_port)
    time.sleep(1)



port.close()