Build Instructions

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• 1

  Step 1: Connect Arduino to Solenoid

  Using the relay description below, the relay is connected to the Arduino and the solenoid. 

  The loading interface is connected to the solenoid with COM connection going to GND of solenoid and GND or solenoid power supply (5V). In this case we use NO so that the relay is normally open and can pass on the information from the arduino. This is seen below.

• 2

  Step 2: Connect Relay to Arduino

  Now the power interface, is connected to the Arduino. In this case the right side goes to the Arduino connection with GND-Arduino GND, VCC-5V, and In-Pin 5

  This will power the relay and will be used to relay information from Pin 5 to control the loading interface. 

  Once it is connected, the Arduino should be connected through USB-C port to computer and the following code should be uploaded (This will test the solenoid and trigger it every 5 sec) :

  const int ledPin = 5; // Define pin 5 as the LED pin
  
  void setup() {
      pinMode(ledPin, OUTPUT); // Set pin 5 as an output
  }
  
  void loop() {
      digitalWrite(ledPin, HIGH); // Turn LED on
      delay(5000); // Wait for 5 seconds
      digitalWrite(ledPin, LOW); // Turn LED off
      delay(5000); // Wait for 5 seconds
  }

  The solenoid should successfully trigger if the solenoid power supply is around 5V. If it is having trouble moving, you may need a bigger power supply..

• 3

  Step 3: Connect Arudino to EMG Sensor

  The EMG sensor comes with a cable that has 4 different connections:
  

  - GNDA

  - VCC

  - NC

  - VOUT

  In here only the GND, VCC, and VOUT connections are used with GND-Arduino GND, VCC-5V, and VOUT-Pin A0. 

  Once these are connected, upload the following code, this code has already created a threshold for how to detect muscle movement and reducing some noise.

  int emgPin = A0;
  int emgValue = 0;
  int baseline = 330; // Initial guess, updates over time
  const int alpha = 10; // Smoothing factor for baseline
  const int relayPin = 5; // Pin connected to the relay
  const int threshold = 100; // Activation threshold
  bool solenoidState = false; // Keeps track of solenoid state
  bool lastTrigger = false;   // Prevents multiple toggles from noise
  
  void setup() {
    Serial.begin(9600);
    pinMode(relayPin, OUTPUT);
    digitalWrite(relayPin, LOW); // Start with relay OFF
  }
  
  void loop() {
    emgValue = analogRead(emgPin);
  
    // Update baseline slowly (adaptive filtering)
    baseline = (baseline * (alpha - 1) + emgValue) / alpha;
  
    // Normalize: Shift signal relative to baseline
    int normalizedValue = emgValue - baseline;
  
    // Detect when signal **crosses threshold from below** (rising edge)
    if (normalizedValue > threshold && !lastTrigger) {
      solenoidState = !solenoidState; // Toggle state
      digitalWrite(relayPin, solenoidState ? HIGH : LOW);
      lastTrigger = true; // Prevent multiple triggers from noise
    }
  
    // Reset lastTrigger when signal goes back below threshold
    if (normalizedValue < threshold - 50) { 
      lastTrigger = false;
    }
  
    // Print normalized value for Serial Plotter
    Serial.print("-200"); Serial.print(",");
    Serial.print("200"); Serial.print(",");
    Serial.println(normalizedValue);
  
    delay(200); // Slow down updates for smoother plotting
  }

  This code also has a toggle state so that the solenoid will remain either locked or unlocked unless muscle movement is shown again rather than immediately unlocking after the initial muscle movement activity is finished. Once the EMG sensor is connected, the electrodes should be placed on the arm, making sure that the reference electrode is on a more static muscle. Below is the video of the solenoid being triggered: 

  https://drive.google.com/file/d/1NAdGZYV3zY0vhmNM1JgDnYkp98jSdAp3/view?usp=sharing

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