README.md

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+# USDA Pecan IOT Tablet Configuration
+
+This repo contains separate branches for each tablet to store the
+individualized software.
+
+Each of:
+
+- jc
+- meyer
+- sheller
+
+All 3 branches implement contain the prerequisites for setting up a
+Systemd service to listen to and control equipment via MQTT, as well
+as sending back relevant diagnostic and statistical information.
+
+Files:
+
+- mqtt_listener.py: The main Python application interacting with MQTT
+- mqtt_listener.service: The file to install to /etc/systemd/system/
+- mqtt_start.sh: The entrypoint from Systemd to Python

mqtt_listener.py

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-import paho.mqtt.client as mqtt
-import re
-from dynio import *
-import time
-
-# State variable to check if HOME is received before POS
-home_received = False
-home = 0
-dxl_io = []
-motor = None
-
-# Functions to run when the corresponding command is received
-def home():
-    global motor, home
-    motor.write_control_table('Torque_Limit', 200)
-    motor.set_velocity_mode()
-    print('velocity mode set')
-    motor.torque_enable()
-    print('torque enabled')
-    motor.set_velocity(300)
-    print('velocity set')
-    time.sleep(1)
-    while motor.read_control_table('Present_Speed') > 0:
-        pass
-    motor.torque_disable()
-    home = motor.get_position()
-    motor.write_control_table('Multi_Turn_Offset', -1 * home)
-    motor.set_extended_position_mode()
-    motor.torque_enable()
-
-def set_pos(num):
-    global motor
-    motor.set_position(num)
-    time.sleep(0.2)
-    while motor.read_control_table('Present_Speed') > 0:
-        pass
-
-def disable_torque():
-    global motor, home_received
-    motor.torque_disable()
-    home_received = False
-
-
-# The callback for when the client receives a CONNACK response from the server.
-def on_connect(client, userdata, flags, rc):
-    print(f"Connected with result code {str(rc)}")
-
-    # Subscribing in on_connect() means that if we lose the connection and
-    # reconnect then subscriptions will be renewed.
-    client.subscribe("/meyer/#")
-
-    # Connect to Dynamixels
-    global dxl_io, motor
-    dxl_io = dxl.DynamixelIO('/dev/ttyACM0')
-    motor = dxl_io.new_mx106(1,1)
-    motor.get_position()
-    motor.write_control_table('Torque_Limit', 200)
-
-
-# The callback for when a PUBLISH message is received from the server.
-def on_message(client, userdata, msg):
-    global home_received, motor
-
-    message = msg.payload.decode()
-    if msg.topic != "/meyer/":
-        return
-
-    if message == "HOME":
-        home()
-        home_received = True
-        time.sleep(0.5)
-        set_pos(int(-250*53.248))
-        client.publish("/meyer/pos", -250.0)
-    elif message == "DISABLE":
-        disable_torque()
-    elif re.match(r"^POS -?\d+$", message):  # This matches POS followed by a number
-        pos_num = int(message.split()[1])  # Extract the number from the message
-        pos_num *= 5.3248
-
-        if pos_num < -25000 or pos_num > 0:  # Check if the number is out of range
-            client.publish("/meyer/error", "Error: Number out of range")
-        elif not home_received:  # Check if HOME was received before POS
-            client.publish("/meyer/error", "Error: HOME command has to be run before POS")
-        else:
-            set_pos(int(pos_num))
-            client.publish("/meyer/pos", round(pos_num / 53.248,1))
-    else:
-        client.publish("/meyer/error", "Error: Unknown command")
-    
-
-client = mqtt.Client()
-client.on_connect = on_connect
-client.on_message = on_message
-
-# Connect to the broker
-client.connect("192.168.1.1", 1883, 60)
-
-# Blocking call that processes network traffic, dispatches callbacks and
-# handles reconnecting.
-client.loop_forever()
-

mqtt_listener.service

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-[Unit]
-Description=MQTT Listener Service
-After=network.target
-
-[Service]
-ExecStart=/home/biqu/mqtt_start.sh
-WorkingDirectory=/home/biqu
-StandardOutput=inherit
-StandardError=inherit
-Restart=always
-User=biqu
-
-[Install]
-WantedBy=multi-user.target
-

mqtt_start.sh

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-#!/bin/bash
-
-# navigate to the directory of the script
-cd /home/biqu/screw_control/
-
-# activate the python environment, if you're using one
-# source /path_to_your_venv/bin/activate
-
-# run the script
-/usr/bin/python3 mqtt_listener.py