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